diff --git a/src/CMakeLists.txt b/src/CMakeLists.txt
index 1e7d64a1f..4c7620063 100644
--- a/src/CMakeLists.txt
+++ b/src/CMakeLists.txt
@@ -38,7 +38,6 @@ configure_file(version.h.cmake ${CMAKE_CURRENT_BINARY_DIR}/version.h @ONLY)
 
 set(keepassx_SOURCES
         core/AutoTypeAssociations.cpp
-        core/AsyncTask.h
         core/AutoTypeMatch.cpp
         core/Compare.cpp
         core/Config.cpp
@@ -52,18 +51,14 @@ set(keepassx_SOURCES
         core/EntrySearcher.cpp
         core/FilePath.cpp
         core/Bootstrap.cpp
-        core/Global.h
         core/Group.cpp
         core/InactivityTimer.cpp
-        core/ListDeleter.h
         core/Merger.cpp
         core/Metadata.cpp
         core/PasswordGenerator.cpp
         core/PassphraseGenerator.cpp
         core/SignalMultiplexer.cpp
         core/ScreenLockListener.cpp
-        core/ScreenLockListener.h
-        core/ScreenLockListenerPrivate.h
         core/ScreenLockListenerPrivate.cpp
         core/TimeDelta.cpp
         core/TimeInfo.cpp
@@ -77,14 +72,11 @@ set(keepassx_SOURCES
         crypto/CryptoHash.cpp
         crypto/Random.cpp
         crypto/SymmetricCipher.cpp
-        crypto/SymmetricCipherBackend.h
         crypto/SymmetricCipherGcrypt.cpp
         crypto/kdf/Kdf.cpp
-        crypto/kdf/Kdf_p.h
         crypto/kdf/AesKdf.cpp
         crypto/kdf/Argon2Kdf.cpp
         format/CsvExporter.cpp
-        format/KeePass1.h
         format/KeePass1Reader.cpp
         format/KeePass2.cpp
         format/KeePass2RandomStream.cpp
@@ -142,7 +134,6 @@ set(keepassx_SOURCES
         gui/entry/AutoTypeMatchModel.cpp
         gui/entry/AutoTypeMatchView.cpp
         gui/entry/EditEntryWidget.cpp
-        gui/entry/EditEntryWidget_p.h
         gui/entry/EntryAttachmentsModel.cpp
         gui/entry/EntryAttachmentsWidget.cpp
         gui/entry/EntryAttributesModel.cpp
@@ -168,11 +159,8 @@ set(keepassx_SOURCES
         gui/wizard/NewDatabaseWizardPageMetaData.cpp
         gui/wizard/NewDatabaseWizardPageEncryption.cpp
         gui/wizard/NewDatabaseWizardPageMasterKey.cpp
-        keys/ChallengeResponseKey.h
         keys/CompositeKey.cpp
-        keys/drivers/YubiKey.h
         keys/FileKey.cpp
-        keys/Key.h
         keys/PasswordKey.cpp
         keys/YkChallengeResponseKey.cpp
         streams/HashedBlockStream.cpp
@@ -181,27 +169,22 @@ set(keepassx_SOURCES
         streams/qtiocompressor.cpp
         streams/StoreDataStream.cpp
         streams/SymmetricCipherStream.cpp
-        totp/totp.h
         totp/totp.cpp)
 if(APPLE)
     set(keepassx_SOURCES
             ${keepassx_SOURCES}
-            core/ScreenLockListenerMac.h
             core/ScreenLockListenerMac.cpp
-            core/MacPasteboard.h
             core/MacPasteboard.cpp)
 endif()
 if(UNIX AND NOT APPLE)
     set(keepassx_SOURCES
             ${keepassx_SOURCES}
-            core/ScreenLockListenerDBus.h
             core/ScreenLockListenerDBus.cpp
             gui/MainWindowAdaptor.cpp)
 endif()
 if(MINGW)
     set(keepassx_SOURCES
             ${keepassx_SOURCES}
-            core/ScreenLockListenerWin.h
             core/ScreenLockListenerWin.cpp)
 endif()
 if(MINGW OR (UNIX AND NOT APPLE))
@@ -243,13 +226,11 @@ set(autotype_SOURCES
         core/Tools.cpp
         autotype/AutoType.cpp
         autotype/AutoTypeAction.cpp
-        autotype/AutoTypePlatformPlugin.h
         autotype/AutoTypeSelectDialog.cpp
         autotype/AutoTypeSelectView.cpp
         autotype/ShortcutWidget.cpp
         autotype/WildcardMatcher.cpp
-        autotype/WindowSelectComboBox.cpp
-        autotype/test/AutoTypeTestInterface.h)
+        autotype/WindowSelectComboBox.cpp)
 
 if(MINGW)
     set(keepassx_SOURCES_MAINEXE ${keepassx_SOURCES_MAINEXE} ${CMAKE_SOURCE_DIR}/share/windows/icon.rc)
diff --git a/src/autotype/AutoType.cpp b/src/autotype/AutoType.cpp
index c2c16bc75..9d6b75557 100644
--- a/src/autotype/AutoType.cpp
+++ b/src/autotype/AutoType.cpp
@@ -43,7 +43,7 @@ AutoType::AutoType(QObject* parent, bool test)
     : QObject(parent)
     , m_autoTypeDelay(0)
     , m_currentGlobalKey(static_cast<Qt::Key>(0))
-    , m_currentGlobalModifiers(0)
+    , m_currentGlobalModifiers(nullptr)
     , m_pluginLoader(new QPluginLoader(this))
     , m_plugin(nullptr)
     , m_executor(nullptr)
@@ -731,8 +731,7 @@ bool AutoType::checkHighRepetition(const QString& string)
 bool AutoType::verifyAutoTypeSyntax(const QString& sequence)
 {
     if (!AutoType::checkSyntax(sequence)) {
-        QMessageBox messageBox;
-        messageBox.critical(nullptr, tr("Auto-Type"), tr("The Syntax of your Auto-Type statement is incorrect!"));
+        QMessageBox::critical(nullptr, tr("Auto-Type"), tr("The Syntax of your Auto-Type statement is incorrect!"));
         return false;
     } else if (AutoType::checkHighDelay(sequence)) {
         QMessageBox::StandardButton reply;
diff --git a/src/autotype/AutoTypeAction.cpp b/src/autotype/AutoTypeAction.cpp
index 0beb19b39..f9d928f0d 100644
--- a/src/autotype/AutoTypeAction.cpp
+++ b/src/autotype/AutoTypeAction.cpp
@@ -87,3 +87,9 @@ void AutoTypeExecutor::execClearField(AutoTypeClearField* action)
 {
     Q_UNUSED(action);
 }
+
+AutoTypeAction::~AutoTypeAction()
+{
+    // This makes sure that AutoTypeAction's vtable is placed
+    // in this translation unit.
+}
diff --git a/src/autotype/AutoTypeAction.h b/src/autotype/AutoTypeAction.h
index 263566dd8..e598b1dcc 100644
--- a/src/autotype/AutoTypeAction.h
+++ b/src/autotype/AutoTypeAction.h
@@ -29,19 +29,17 @@ class AutoTypeExecutor;
 class KEEPASSX_EXPORT AutoTypeAction
 {
 public:
-    virtual ~AutoTypeAction()
-    {
-    }
     virtual AutoTypeAction* clone() = 0;
     virtual void accept(AutoTypeExecutor* executor) = 0;
+    virtual ~AutoTypeAction();
 };
 
 class KEEPASSX_EXPORT AutoTypeChar : public AutoTypeAction
 {
 public:
     explicit AutoTypeChar(const QChar& character);
-    AutoTypeAction* clone();
-    void accept(AutoTypeExecutor* executor);
+    AutoTypeAction* clone() override;
+    void accept(AutoTypeExecutor* executor) override;
 
     const QChar character;
 };
@@ -50,8 +48,8 @@ class KEEPASSX_EXPORT AutoTypeKey : public AutoTypeAction
 {
 public:
     explicit AutoTypeKey(Qt::Key key);
-    AutoTypeAction* clone();
-    void accept(AutoTypeExecutor* executor);
+    AutoTypeAction* clone() override;
+    void accept(AutoTypeExecutor* executor) override;
 
     const Qt::Key key;
 };
@@ -60,8 +58,8 @@ class KEEPASSX_EXPORT AutoTypeDelay : public AutoTypeAction
 {
 public:
     explicit AutoTypeDelay(int delayMs);
-    AutoTypeAction* clone();
-    void accept(AutoTypeExecutor* executor);
+    AutoTypeAction* clone() override;
+    void accept(AutoTypeExecutor* executor) override;
 
     const int delayMs;
 };
@@ -70,8 +68,8 @@ class KEEPASSX_EXPORT AutoTypeClearField : public AutoTypeAction
 {
 public:
     AutoTypeClearField();
-    AutoTypeAction* clone();
-    void accept(AutoTypeExecutor* executor);
+    AutoTypeAction* clone() override;
+    void accept(AutoTypeExecutor* executor) override;
 };
 
 class KEEPASSX_EXPORT AutoTypeExecutor
diff --git a/src/autotype/AutoTypeSelectDialog.cpp b/src/autotype/AutoTypeSelectDialog.cpp
index 7178c70f9..fe0ba811e 100644
--- a/src/autotype/AutoTypeSelectDialog.cpp
+++ b/src/autotype/AutoTypeSelectDialog.cpp
@@ -69,7 +69,7 @@ AutoTypeSelectDialog::AutoTypeSelectDialog(QWidget* parent)
 
     connect(m_view, SIGNAL(activated(QModelIndex)), SLOT(emitMatchActivated(QModelIndex)));
     connect(m_view, SIGNAL(clicked(QModelIndex)), SLOT(emitMatchActivated(QModelIndex)));
-    connect(m_view->model(), SIGNAL(rowsRemoved(QModelIndex, int, int)), SLOT(matchRemoved()));
+    connect(m_view->model(), SIGNAL(rowsRemoved(QModelIndex,int,int)), SLOT(matchRemoved()));
     connect(m_view, SIGNAL(rejected()), SLOT(reject()));
     layout->addWidget(m_view);
 
diff --git a/src/autotype/ShortcutWidget.cpp b/src/autotype/ShortcutWidget.cpp
index 95174e430..3dcc669d9 100644
--- a/src/autotype/ShortcutWidget.cpp
+++ b/src/autotype/ShortcutWidget.cpp
@@ -24,7 +24,7 @@
 ShortcutWidget::ShortcutWidget(QWidget* parent)
     : QLineEdit(parent)
     , m_key(static_cast<Qt::Key>(0))
-    , m_modifiers(0)
+    , m_modifiers(nullptr)
     , m_locked(false)
 {
     setReadOnly(true);
@@ -58,7 +58,7 @@ void ShortcutWidget::setShortcut(Qt::Key key, Qt::KeyboardModifiers modifiers)
 void ShortcutWidget::resetShortcut()
 {
     m_key = static_cast<Qt::Key>(0);
-    m_modifiers = 0;
+    m_modifiers = nullptr;
     m_locked = false;
     autoType()->unregisterGlobalShortcut();
 }
diff --git a/src/autotype/WildcardMatcher.cpp b/src/autotype/WildcardMatcher.cpp
index bac785897..6afd10cee 100644
--- a/src/autotype/WildcardMatcher.cpp
+++ b/src/autotype/WildcardMatcher.cpp
@@ -18,12 +18,13 @@
 #include "WildcardMatcher.h"
 
 #include <QStringList>
+#include <utility>
 
 const QChar WildcardMatcher::Wildcard = '*';
 const Qt::CaseSensitivity WildcardMatcher::Sensitivity = Qt::CaseInsensitive;
 
-WildcardMatcher::WildcardMatcher(const QString& text)
-    : m_text(text)
+WildcardMatcher::WildcardMatcher(QString  text)
+    : m_text(std::move(text))
 {
 }
 
diff --git a/src/autotype/WildcardMatcher.h b/src/autotype/WildcardMatcher.h
index 6ef48743b..5be6f5e40 100644
--- a/src/autotype/WildcardMatcher.h
+++ b/src/autotype/WildcardMatcher.h
@@ -23,7 +23,7 @@
 class WildcardMatcher
 {
 public:
-    explicit WildcardMatcher(const QString& text);
+    explicit WildcardMatcher(QString  text);
     bool match(const QString& pattern);
 
     static const QChar Wildcard;
diff --git a/src/autotype/xcb/AutoTypeXCB.cpp b/src/autotype/xcb/AutoTypeXCB.cpp
index d2030b771..5198468cf 100644
--- a/src/autotype/xcb/AutoTypeXCB.cpp
+++ b/src/autotype/xcb/AutoTypeXCB.cpp
@@ -50,7 +50,7 @@ AutoTypePlatformX11::AutoTypePlatformX11()
                      << "xfce4-panel"; // Xfce 4
 
     m_currentGlobalKey = static_cast<Qt::Key>(0);
-    m_currentGlobalModifiers = 0;
+    m_currentGlobalModifiers = nullptr;
 
     m_keysymTable = nullptr;
     m_xkb = nullptr;
@@ -197,7 +197,7 @@ void AutoTypePlatformX11::unregisterGlobalShortcut(Qt::Key key, Qt::KeyboardModi
     XUngrabKey(m_dpy, keycode, nativeModifiers | Mod2Mask | LockMask, m_rootWindow);
 
     m_currentGlobalKey = static_cast<Qt::Key>(0);
-    m_currentGlobalModifiers = 0;
+    m_currentGlobalModifiers = nullptr;
     m_currentGlobalKeycode = 0;
     m_currentGlobalNativeModifiers = 0;
 }
@@ -496,7 +496,7 @@ void AutoTypePlatformX11::updateKeymap()
     m_xkb = getKeyboard();
 
     XDisplayKeycodes(m_dpy, &m_minKeycode, &m_maxKeycode);
-    if (m_keysymTable != NULL)
+    if (m_keysymTable != nullptr)
         XFree(m_keysymTable);
     m_keysymTable = XGetKeyboardMapping(m_dpy, m_minKeycode, m_maxKeycode - m_minKeycode + 1, &m_keysymPerKeycode);
 
diff --git a/src/browser/BrowserAction.cpp b/src/browser/BrowserAction.cpp
index fcbc318ee..ccd17c5fd 100644
--- a/src/browser/BrowserAction.cpp
+++ b/src/browser/BrowserAction.cpp
@@ -468,7 +468,7 @@ QJsonObject BrowserAction::decryptMessage(const QString& message, const QString&
     return getErrorReply(action, ERROR_KEEPASS_CANNOT_DECRYPT_MESSAGE);
 }
 
-QString BrowserAction::encrypt(const QString plaintext, const QString nonce)
+QString BrowserAction::encrypt(const QString& plaintext, const QString& nonce)
 {
     QMutexLocker locker(&m_mutex);
     const QByteArray ma = plaintext.toUtf8();
@@ -496,7 +496,7 @@ QString BrowserAction::encrypt(const QString plaintext, const QString nonce)
     return QString();
 }
 
-QByteArray BrowserAction::decrypt(const QString encrypted, const QString nonce)
+QByteArray BrowserAction::decrypt(const QString& encrypted, const QString& nonce)
 {
     QMutexLocker locker(&m_mutex);
     const QByteArray ma = base64Decode(encrypted);
@@ -546,14 +546,14 @@ QJsonObject BrowserAction::getJsonObject(const uchar* pArray, const uint len) co
     return doc.object();
 }
 
-QJsonObject BrowserAction::getJsonObject(const QByteArray ba) const
+QJsonObject BrowserAction::getJsonObject(const QByteArray& ba) const
 {
     QJsonParseError err;
     QJsonDocument doc(QJsonDocument::fromJson(ba, &err));
     return doc.object();
 }
 
-QByteArray BrowserAction::base64Decode(const QString str)
+QByteArray BrowserAction::base64Decode(const QString& str)
 {
     return QByteArray::fromBase64(str.toUtf8());
 }
diff --git a/src/browser/BrowserAction.h b/src/browser/BrowserAction.h
index 5a7c83bf8..b7a60938f 100644
--- a/src/browser/BrowserAction.h
+++ b/src/browser/BrowserAction.h
@@ -73,14 +73,14 @@ private:
 
     QString encryptMessage(const QJsonObject& message, const QString& nonce);
     QJsonObject decryptMessage(const QString& message, const QString& nonce, const QString& action = QString());
-    QString encrypt(const QString plaintext, const QString nonce);
-    QByteArray decrypt(const QString encrypted, const QString nonce);
+    QString encrypt(const QString& plaintext, const QString& nonce);
+    QByteArray decrypt(const QString& encrypted, const QString& nonce);
 
     QString getBase64FromKey(const uchar* array, const uint len);
     QByteArray getQByteArray(const uchar* array, const uint len) const;
     QJsonObject getJsonObject(const uchar* pArray, const uint len) const;
-    QJsonObject getJsonObject(const QByteArray ba) const;
-    QByteArray base64Decode(const QString str);
+    QJsonObject getJsonObject(const QByteArray& ba) const;
+    QByteArray base64Decode(const QString& str);
     QString incrementNonce(const QString& nonce);
 
 private:
diff --git a/src/browser/BrowserEntryConfig.h b/src/browser/BrowserEntryConfig.h
index 3b808b7e0..f1363f421 100644
--- a/src/browser/BrowserEntryConfig.h
+++ b/src/browser/BrowserEntryConfig.h
@@ -35,7 +35,7 @@ class BrowserEntryConfig : public QObject
     Q_PROPERTY(QString Realm READ realm WRITE setRealm)
 
 public:
-    BrowserEntryConfig(QObject* object = 0);
+    BrowserEntryConfig(QObject* object = nullptr);
 
     bool load(const Entry* entry);
     void save(Entry* entry);
diff --git a/src/browser/BrowserService.cpp b/src/browser/BrowserService.cpp
index 9917ded3c..cca76c15f 100644
--- a/src/browser/BrowserService.cpp
+++ b/src/browser/BrowserService.cpp
@@ -145,7 +145,7 @@ QString BrowserService::storeKey(const QString& key)
 
     if (thread() != QThread::currentThread()) {
         QMetaObject::invokeMethod(
-            this, "storeKey", Qt::BlockingQueuedConnection, Q_RETURN_ARG(QString, id), Q_ARG(const QString&, key));
+            this, "storeKey", Qt::BlockingQueuedConnection, Q_RETURN_ARG(QString, id), Q_ARG(QString, key));
         return id;
     }
 
@@ -213,11 +213,11 @@ QJsonArray BrowserService::findMatchingEntries(const QString& id,
                                   "findMatchingEntries",
                                   Qt::BlockingQueuedConnection,
                                   Q_RETURN_ARG(QJsonArray, result),
-                                  Q_ARG(const QString&, id),
-                                  Q_ARG(const QString&, url),
-                                  Q_ARG(const QString&, submitUrl),
-                                  Q_ARG(const QString&, realm),
-                                  Q_ARG(const StringPairList&, keyList));
+                                  Q_ARG(QString, id),
+                                  Q_ARG(QString, url),
+                                  Q_ARG(QString, submitUrl),
+                                  Q_ARG(QString, realm),
+                                  Q_ARG(StringPairList, keyList));
         return result;
     }
 
@@ -279,12 +279,12 @@ void BrowserService::addEntry(const QString& id,
         QMetaObject::invokeMethod(this,
                                   "addEntry",
                                   Qt::BlockingQueuedConnection,
-                                  Q_ARG(const QString&, id),
-                                  Q_ARG(const QString&, login),
-                                  Q_ARG(const QString&, password),
-                                  Q_ARG(const QString&, url),
-                                  Q_ARG(const QString&, submitUrl),
-                                  Q_ARG(const QString&, realm),
+                                  Q_ARG(QString, id),
+                                  Q_ARG(QString, login),
+                                  Q_ARG(QString, password),
+                                  Q_ARG(QString, url),
+                                  Q_ARG(QString, submitUrl),
+                                  Q_ARG(QString, realm),
                                   Q_ARG(Database*, selectedDb));
     }
 
@@ -332,12 +332,12 @@ void BrowserService::updateEntry(const QString& id,
         QMetaObject::invokeMethod(this,
                                   "updateEntry",
                                   Qt::BlockingQueuedConnection,
-                                  Q_ARG(const QString&, id),
-                                  Q_ARG(const QString&, uuid),
-                                  Q_ARG(const QString&, login),
-                                  Q_ARG(const QString&, password),
-                                  Q_ARG(const QString&, url),
-                                  Q_ARG(const QString&, submitUrl));
+                                  Q_ARG(QString, id),
+                                  Q_ARG(QString, uuid),
+                                  Q_ARG(QString, login),
+                                  Q_ARG(QString, password),
+                                  Q_ARG(QString, url),
+                                  Q_ARG(QString, submitUrl));
     }
 
     Database* db = selectedDatabase();
@@ -362,7 +362,7 @@ void BrowserService::updateEntry(const QString& id,
         if (!browserSettings()->alwaysAllowUpdate()) {
             QMessageBox msgBox;
             msgBox.setWindowTitle(tr("KeePassXC: Update Entry"));
-            msgBox.setText(tr("Do you want to update the information in %1 - %2?").arg(QUrl(url).host()).arg(username));
+            msgBox.setText(tr("Do you want to update the information in %1 - %2?").arg(QUrl(url).host(), username));
             msgBox.setStandardButtons(QMessageBox::Yes);
             msgBox.addButton(QMessageBox::No);
             msgBox.setDefaultButton(QMessageBox::No);
@@ -421,7 +421,7 @@ QList<Entry*> BrowserService::searchEntries(const QString& url, const StringPair
             if (DatabaseWidget* dbWidget = qobject_cast<DatabaseWidget*>(m_dbTabWidget->widget(i))) {
                 if (Database* db = dbWidget->database()) {
                      // Check if database is connected with KeePassXC-Browser
-                    for (const StringPair keyPair : keyList) {
+                    for (const StringPair& keyPair : keyList) {
                         QString key = db->metadata()->customData()->value(QLatin1String(ASSOCIATE_KEY_PREFIX) + keyPair.first);
                         if (!key.isEmpty() && keyPair.second == key) {
                             databases << db;
@@ -481,16 +481,16 @@ void BrowserService::convertAttributesToCustomData(Database *currentDb)
     progress.reset();
 
     if (counter > 0) {
-        QMessageBox::information(0, tr("KeePassXC: Converted KeePassHTTP attributes"),
+        QMessageBox::information(nullptr, tr("KeePassXC: Converted KeePassHTTP attributes"),
                                  tr("Successfully converted attributes from %1 entry(s).\n"
                                     "Moved %2 keys to custom data.", "").arg(counter).arg(keyCounter),
                                  QMessageBox::Ok);
     } else if (counter == 0 && keyCounter > 0) {
-        QMessageBox::information(0, tr("KeePassXC: Converted KeePassHTTP attributes"),
+        QMessageBox::information(nullptr, tr("KeePassXC: Converted KeePassHTTP attributes"),
                                  tr("Successfully moved %n keys to custom data.", "", keyCounter),
                                  QMessageBox::Ok);
     } else {
-        QMessageBox::information(0, tr("KeePassXC: No entry with KeePassHTTP attributes found!"),
+        QMessageBox::information(nullptr, tr("KeePassXC: No entry with KeePassHTTP attributes found!"),
                                  tr("The active database does not contain an entry with KeePassHTTP attributes."),
                                  QMessageBox::Ok);
     }
diff --git a/src/browser/BrowserSettings.cpp b/src/browser/BrowserSettings.cpp
index 630d0ff18..646c6c4d3 100644
--- a/src/browser/BrowserSettings.cpp
+++ b/src/browser/BrowserSettings.cpp
@@ -169,7 +169,7 @@ QString BrowserSettings::customProxyLocation()
     return config()->get("Browser/CustomProxyLocation", "").toString();
 }
 
-void BrowserSettings::setCustomProxyLocation(QString location)
+void BrowserSettings::setCustomProxyLocation(const QString& location)
 {
     config()->set("Browser/CustomProxyLocation", location);
 }
@@ -364,7 +364,7 @@ QString BrowserSettings::passwordExcludedChars()
     return config()->get("generator/ExcludedChars", PasswordGenerator::DefaultExcludedChars).toString();
 }
 
-void BrowserSettings::setPasswordExcludedChars(QString chars)
+void BrowserSettings::setPasswordExcludedChars(const QString& chars)
 {
     config()->set("generator/ExcludedChars", chars);
 }
@@ -384,7 +384,7 @@ QString BrowserSettings::passPhraseWordSeparator()
     return config()->get("generator/WordSeparator", PassphraseGenerator::DefaultSeparator).toString();
 }
 
-void BrowserSettings::setPassPhraseWordSeparator(QString separator)
+void BrowserSettings::setPassPhraseWordSeparator(const QString& separator)
 {
     config()->set("generator/WordSeparator", separator);
 }
@@ -496,7 +496,7 @@ QString BrowserSettings::generatePassword()
     }
 }
 
-void BrowserSettings::updateBinaryPaths(QString customProxyLocation)
+void BrowserSettings::updateBinaryPaths(const QString& customProxyLocation)
 {
     bool isProxy = supportBrowserProxy();
     m_hostInstaller.updateBinaryPaths(isProxy, customProxyLocation);
diff --git a/src/browser/BrowserSettings.h b/src/browser/BrowserSettings.h
index 2e7c55ec6..92cdcd16d 100644
--- a/src/browser/BrowserSettings.h
+++ b/src/browser/BrowserSettings.h
@@ -59,7 +59,7 @@ public:
     bool useCustomProxy();
     void setUseCustomProxy(bool enabled);
     QString customProxyLocation();
-    void setCustomProxyLocation(QString location);
+    void setCustomProxyLocation(const QString& location);
     bool updateBinaryPath();
     void setUpdateBinaryPath(bool enabled);
     bool chromeSupport();
@@ -98,11 +98,11 @@ public:
     bool advancedMode();
     void setAdvancedMode(bool advancedMode);
     QString passwordExcludedChars();
-    void setPasswordExcludedChars(QString chars);
+    void setPasswordExcludedChars(const QString& chars);
     int passPhraseWordCount();
     void setPassPhraseWordCount(int wordCount);
     QString passPhraseWordSeparator();
-    void setPassPhraseWordSeparator(QString separator);
+    void setPassPhraseWordSeparator(const QString& separator);
     int generatorType();
     void setGeneratorType(int type);
     bool passwordEveryGroup();
@@ -114,7 +114,7 @@ public:
     PasswordGenerator::CharClasses passwordCharClasses();
     PasswordGenerator::GeneratorFlags passwordGeneratorFlags();
     QString generatePassword();
-    void updateBinaryPaths(QString customProxyLocation = QString());
+    void updateBinaryPaths(const QString& customProxyLocation = QString());
     bool checkIfProxyExists(QString& path);
 
 private:
diff --git a/src/browser/HostInstaller.cpp b/src/browser/HostInstaller.cpp
index a3ad608d4..f4585febe 100644
--- a/src/browser/HostInstaller.cpp
+++ b/src/browser/HostInstaller.cpp
@@ -111,7 +111,7 @@ void HostInstaller::installBrowser(SupportedBrowsers browser,
         // Always create the script file
         QJsonObject script = constructFile(browser, proxy, location);
         if (!saveFile(browser, script)) {
-            QMessageBox::critical(0,
+            QMessageBox::critical(nullptr,
                                   tr("KeePassXC: Cannot save file!"),
                                   tr("Cannot save the native messaging script file."),
                                   QMessageBox::Ok);
diff --git a/src/browser/NativeMessagingHost.h b/src/browser/NativeMessagingHost.h
index 869af9e24..774306d30 100644
--- a/src/browser/NativeMessagingHost.h
+++ b/src/browser/NativeMessagingHost.h
@@ -31,7 +31,7 @@ class NativeMessagingHost : public NativeMessagingBase
     typedef QList<QLocalSocket*> SocketList;
 
 public:
-    explicit NativeMessagingHost(DatabaseTabWidget* parent = 0, const bool enabled = false);
+    explicit NativeMessagingHost(DatabaseTabWidget* parent = nullptr, const bool enabled = false);
     ~NativeMessagingHost();
     int init();
     void run();
@@ -41,8 +41,8 @@ signals:
     void quit();
 
 private:
-    void readLength();
-    bool readStdIn(const quint32 length);
+    void readLength() override;
+    bool readStdIn(const quint32 length) override;
     void sendReplyToAllClients(const QJsonObject& json);
 
 private slots:
diff --git a/src/cli/Add.h b/src/cli/Add.h
index 5769249c9..dd0c3d8b5 100644
--- a/src/cli/Add.h
+++ b/src/cli/Add.h
@@ -25,7 +25,7 @@ class Add : public Command
 public:
     Add();
     ~Add();
-    int execute(const QStringList& arguments);
+    int execute(const QStringList& arguments) override;
 };
 
 #endif // KEEPASSXC_ADD_H
diff --git a/src/cli/CMakeLists.txt b/src/cli/CMakeLists.txt
index f6377aa07..37a085ad3 100644
--- a/src/cli/CMakeLists.txt
+++ b/src/cli/CMakeLists.txt
@@ -15,31 +15,18 @@
 
 set(cli_SOURCES
         Add.cpp
-        Add.h
         Clip.cpp
-        Clip.h
         Command.cpp
-        Command.h
         Diceware.cpp
-        Diceware.h
         Edit.cpp
-        Edit.h
         Estimate.cpp
-        Estimate.h
         Extract.cpp
-        Extract.h
         Generate.cpp
-        Generate.h
         List.cpp
-        List.h
         Locate.cpp
-        Locate.h
         Merge.cpp
-        Merge.h
         Remove.cpp
-        Remove.h
-        Show.cpp
-        Show.h)
+        Show.cpp)
 
 add_library(cli STATIC ${cli_SOURCES})
 target_link_libraries(cli Qt5::Core Qt5::Widgets)
diff --git a/src/cli/Clip.cpp b/src/cli/Clip.cpp
index 2268c6624..a9135eff4 100644
--- a/src/cli/Clip.cpp
+++ b/src/cli/Clip.cpp
@@ -71,7 +71,7 @@ int Clip::execute(const QStringList& arguments)
     return clipEntry(db, args.at(1), args.value(2));
 }
 
-int Clip::clipEntry(Database* database, QString entryPath, QString timeout)
+int Clip::clipEntry(Database* database, const QString& entryPath, const QString& timeout)
 {
     TextStream err(Utils::STDERR);
 
diff --git a/src/cli/Clip.h b/src/cli/Clip.h
index e94231236..e5e6390ae 100644
--- a/src/cli/Clip.h
+++ b/src/cli/Clip.h
@@ -25,8 +25,8 @@ class Clip : public Command
 public:
     Clip();
     ~Clip();
-    int execute(const QStringList& arguments);
-    int clipEntry(Database* database, QString entryPath, QString timeout);
+    int execute(const QStringList& arguments) override;
+    int clipEntry(Database* database, const QString& entryPath, const QString& timeout);
 };
 
 #endif // KEEPASSXC_CLIP_H
diff --git a/src/cli/Command.cpp b/src/cli/Command.cpp
index c85e5d95d..a95676ff0 100644
--- a/src/cli/Command.cpp
+++ b/src/cli/Command.cpp
@@ -71,7 +71,7 @@ void populateCommands()
     }
 }
 
-Command* Command::getCommand(QString commandName)
+Command* Command::getCommand(const QString& commandName)
 {
     populateCommands();
     if (commands.contains(commandName)) {
diff --git a/src/cli/Command.h b/src/cli/Command.h
index 7ad49440a..4e4e076de 100644
--- a/src/cli/Command.h
+++ b/src/cli/Command.h
@@ -35,7 +35,7 @@ public:
     QString getDescriptionLine();
 
     static QList<Command*> getCommands();
-    static Command* getCommand(QString commandName);
+    static Command* getCommand(const QString& commandName);
 };
 
 #endif // KEEPASSXC_COMMAND_H
diff --git a/src/cli/Diceware.h b/src/cli/Diceware.h
index 61fe724ca..f439681b7 100644
--- a/src/cli/Diceware.h
+++ b/src/cli/Diceware.h
@@ -25,7 +25,7 @@ class Diceware : public Command
 public:
     Diceware();
     ~Diceware();
-    int execute(const QStringList& arguments);
+    int execute(const QStringList& arguments) override;
 };
 
 #endif // KEEPASSXC_DICEWARE_H
diff --git a/src/cli/Edit.h b/src/cli/Edit.h
index 2c413bea0..001b5abaf 100644
--- a/src/cli/Edit.h
+++ b/src/cli/Edit.h
@@ -25,7 +25,7 @@ class Edit : public Command
 public:
     Edit();
     ~Edit();
-    int execute(const QStringList& arguments);
+    int execute(const QStringList& arguments) override;
 };
 
 #endif // KEEPASSXC_EDIT_H
diff --git a/src/cli/Estimate.h b/src/cli/Estimate.h
index 15f922752..c15fed9b3 100644
--- a/src/cli/Estimate.h
+++ b/src/cli/Estimate.h
@@ -25,7 +25,7 @@ class Estimate : public Command
 public:
     Estimate();
     ~Estimate();
-    int execute(const QStringList& arguments);
+    int execute(const QStringList& arguments) override;
 };
 
 #endif // KEEPASSXC_ESTIMATE_H
diff --git a/src/cli/Extract.cpp b/src/cli/Extract.cpp
index 32b1bc028..c0b1b1119 100644
--- a/src/cli/Extract.cpp
+++ b/src/cli/Extract.cpp
@@ -77,7 +77,7 @@ int Extract::execute(const QStringList& arguments)
         auto fileKey = QSharedPointer<FileKey>::create();
         QString errorMsg;
         if (!fileKey->load(keyFilePath, &errorMsg)) {
-            err << QObject::tr("Failed to load key file %1: %2").arg(keyFilePath).arg(errorMsg) << endl;
+            err << QObject::tr("Failed to load key file %1: %2").arg(keyFilePath, errorMsg) << endl;
             return EXIT_FAILURE;
         }
 
diff --git a/src/cli/Extract.h b/src/cli/Extract.h
index 2939afddb..1a4f6288b 100644
--- a/src/cli/Extract.h
+++ b/src/cli/Extract.h
@@ -25,7 +25,7 @@ class Extract : public Command
 public:
     Extract();
     ~Extract();
-    int execute(const QStringList& arguments);
+    int execute(const QStringList& arguments) override;
 };
 
 #endif // KEEPASSXC_EXTRACT_H
diff --git a/src/cli/Generate.h b/src/cli/Generate.h
index 607fc105c..64ef81623 100644
--- a/src/cli/Generate.h
+++ b/src/cli/Generate.h
@@ -25,7 +25,7 @@ class Generate : public Command
 public:
     Generate();
     ~Generate();
-    int execute(const QStringList& arguments);
+    int execute(const QStringList& arguments) override;
 };
 
 #endif // KEEPASSXC_GENERATE_H
diff --git a/src/cli/List.h b/src/cli/List.h
index 5697d9390..92ade262b 100644
--- a/src/cli/List.h
+++ b/src/cli/List.h
@@ -25,7 +25,7 @@ class List : public Command
 public:
     List();
     ~List();
-    int execute(const QStringList& arguments);
+    int execute(const QStringList& arguments) override;
     int listGroup(Database* database, bool recursive, const QString& groupPath = {});
 };
 
diff --git a/src/cli/Locate.h b/src/cli/Locate.h
index 3355d41ec..ae32951b9 100644
--- a/src/cli/Locate.h
+++ b/src/cli/Locate.h
@@ -25,7 +25,7 @@ class Locate : public Command
 public:
     Locate();
     ~Locate();
-    int execute(const QStringList& arguments);
+    int execute(const QStringList& arguments) override;
     int locateEntry(Database* database, const QString& searchTerm);
 };
 
diff --git a/src/cli/Merge.h b/src/cli/Merge.h
index 496c66b86..1f138b65f 100644
--- a/src/cli/Merge.h
+++ b/src/cli/Merge.h
@@ -25,7 +25,7 @@ class Merge : public Command
 public:
     Merge();
     ~Merge();
-    int execute(const QStringList& arguments);
+    int execute(const QStringList& arguments) override;
 };
 
 #endif // KEEPASSXC_MERGE_H
diff --git a/src/cli/Remove.h b/src/cli/Remove.h
index 33d62f4bd..d45e04af2 100644
--- a/src/cli/Remove.h
+++ b/src/cli/Remove.h
@@ -27,7 +27,7 @@ class Remove : public Command
 public:
     Remove();
     ~Remove();
-    int execute(const QStringList& arguments);
+    int execute(const QStringList& arguments) override;
     int removeEntry(Database* database, const QString& databasePath, const QString& entryPath);
 };
 
diff --git a/src/cli/Show.h b/src/cli/Show.h
index fe16546c3..6d49d1207 100644
--- a/src/cli/Show.h
+++ b/src/cli/Show.h
@@ -25,7 +25,7 @@ class Show : public Command
 public:
     Show();
     ~Show();
-    int execute(const QStringList& arguments);
+    int execute(const QStringList& arguments) override;
     int showEntry(Database* database, QStringList attributes, const QString& entryPath);
 };
 
diff --git a/src/core/AutoTypeMatch.cpp b/src/core/AutoTypeMatch.cpp
index 9b7940f4d..13b037bb6 100644
--- a/src/core/AutoTypeMatch.cpp
+++ b/src/core/AutoTypeMatch.cpp
@@ -18,6 +18,8 @@
 
 #include "AutoTypeMatch.h"
 
+#include <utility>
+
 AutoTypeMatch::AutoTypeMatch()
     : entry(nullptr)
     , sequence()
@@ -26,7 +28,7 @@ AutoTypeMatch::AutoTypeMatch()
 
 AutoTypeMatch::AutoTypeMatch(Entry* entry, QString sequence)
     : entry(entry)
-    , sequence(sequence)
+    , sequence(std::move(sequence))
 {
 }
 
diff --git a/src/core/CsvParser.cpp b/src/core/CsvParser.cpp
index a66c919b2..e545d1db4 100644
--- a/src/core/CsvParser.cpp
+++ b/src/core/CsvParser.cpp
@@ -1,4 +1,4 @@
-/*
+/*
  *  Copyright (C) 2016 Enrico Mariotti <enricomariotti@yahoo.it>
  *  Copyright (C) 2017 KeePassXC Team <team@keepassxc.org>
  *
@@ -327,7 +327,7 @@ bool CsvParser::isText(QChar c) const
     return !((isCRLF(c)) || (isSeparator(c)));
 }
 
-bool CsvParser::isEmptyRow(CsvRow row) const
+bool CsvParser::isEmptyRow(const CsvRow& row) const
 {
     CsvRow::const_iterator it = row.constBegin();
     for (; it != row.constEnd(); ++it)
@@ -414,7 +414,7 @@ int CsvParser::getCsvRows() const
     return m_table.size();
 }
 
-void CsvParser::appendStatusMsg(QString s, bool isCritical)
+void CsvParser::appendStatusMsg(const QString& s, bool isCritical)
 {
     m_statusMsg += QObject::tr("%1: (row, col) %2,%3").arg(s, m_currRow, m_currCol).append("\n");
     m_isGood = !isCritical;
diff --git a/src/core/CsvParser.h b/src/core/CsvParser.h
index 323023114..d90e8300a 100644
--- a/src/core/CsvParser.h
+++ b/src/core/CsvParser.h
@@ -83,7 +83,7 @@ private:
     bool isCRLF(const QChar& c) const;
     bool isSpace(const QChar& c) const;
     bool isTab(const QChar& c) const;
-    bool isEmptyRow(CsvRow row) const;
+    bool isEmptyRow(const CsvRow& row) const;
     bool parseFile();
     void parseRecord();
     void parseField(CsvRow& row);
@@ -96,7 +96,7 @@ private:
     void clear();
     bool skipEndline();
     void skipLine();
-    void appendStatusMsg(QString s, bool isCritical = false);
+    void appendStatusMsg(const QString& s, bool isCritical = false);
 };
 
 #endif // CSVPARSER_H
diff --git a/src/core/Database.cpp b/src/core/Database.cpp
index 5116fd199..fe9ef600b 100644
--- a/src/core/Database.cpp
+++ b/src/core/Database.cpp
@@ -25,6 +25,7 @@
 #include <QTextStream>
 #include <QTimer>
 #include <QXmlStreamReader>
+#include <utility>
 
 #include "cli/Utils.h"
 #include "core/Clock.h"
@@ -315,7 +316,7 @@ void Database::setCompressionAlgo(Database::CompressionAlgorithm algo)
  * @param updateTransformSalt true to update the transform salt
  * @return true on success
  */
-bool Database::setKey(QSharedPointer<const CompositeKey> key, bool updateChangedTime, bool updateTransformSalt)
+bool Database::setKey(const QSharedPointer<const CompositeKey>& key, bool updateChangedTime, bool updateTransformSalt)
 {
     if (!key) {
         m_data.key.reset();
@@ -354,7 +355,7 @@ bool Database::hasKey() const
     return m_data.hasKey;
 }
 
-bool Database::verifyKey(QSharedPointer<CompositeKey> key) const
+bool Database::verifyKey(const QSharedPointer<CompositeKey>& key) const
 {
     Q_ASSERT(hasKey());
 
@@ -492,7 +493,7 @@ Database* Database::openDatabaseFile(const QString& fileName, QSharedPointer<con
     }
 
     KeePass2Reader reader;
-    Database* db = reader.readDatabase(&dbFile, key);
+    Database* db = reader.readDatabase(&dbFile, std::move(key));
     if (reader.hasError()) {
         qCritical("Error while parsing the database: %s", qPrintable(reader.errorString()));
         return nullptr;
@@ -501,7 +502,7 @@ Database* Database::openDatabaseFile(const QString& fileName, QSharedPointer<con
     return db;
 }
 
-Database* Database::unlockFromStdin(QString databaseFilename, QString keyFilename, FILE* outputDescriptor, FILE* errorDescriptor)
+Database* Database::unlockFromStdin(const QString& databaseFilename, const QString& keyFilename, FILE* outputDescriptor, FILE* errorDescriptor)
 {
     auto compositeKey = QSharedPointer<CompositeKey>::create();
     QTextStream out(outputDescriptor);
@@ -553,7 +554,7 @@ Database* Database::unlockFromStdin(QString databaseFilename, QString keyFilenam
  * @param backup Backup the existing database file, if exists
  * @return error string, if any
  */
-QString Database::saveToFile(QString filePath, bool atomic, bool backup)
+QString Database::saveToFile(const QString& filePath, bool atomic, bool backup)
 {
     QString error;
     if (atomic) {
@@ -633,7 +634,7 @@ QString Database::writeDatabase(QIODevice* device)
  * @param filePath Path to the file to backup
  * @return
  */
-bool Database::backupDatabase(QString filePath)
+bool Database::backupDatabase(const QString& filePath)
 {
     QString backupFilePath = filePath;
     auto re = QRegularExpression("\\.kdbx$|(?<!\\.kdbx)$", QRegularExpression::CaseInsensitiveOption);
@@ -652,7 +653,7 @@ void Database::setKdf(QSharedPointer<Kdf> kdf)
     m_data.kdf = std::move(kdf);
 }
 
-bool Database::changeKdf(QSharedPointer<Kdf> kdf)
+bool Database::changeKdf(const QSharedPointer<Kdf>& kdf)
 {
     kdf->randomizeSeed();
     QByteArray transformedMasterKey;
diff --git a/src/core/Database.h b/src/core/Database.h
index 7108ded31..692444f4d 100644
--- a/src/core/Database.h
+++ b/src/core/Database.h
@@ -110,9 +110,9 @@ public:
     void setCipher(const QUuid& cipher);
     void setCompressionAlgo(Database::CompressionAlgorithm algo);
     void setKdf(QSharedPointer<Kdf> kdf);
-    bool setKey(QSharedPointer<const CompositeKey> key, bool updateChangedTime = true, bool updateTransformSalt = false);
+    bool setKey(const QSharedPointer<const CompositeKey>& key, bool updateChangedTime = true, bool updateTransformSalt = false);
     bool hasKey() const;
-    bool verifyKey(QSharedPointer<CompositeKey> key) const;
+    bool verifyKey(const QSharedPointer<CompositeKey>& key) const;
     QVariantMap& publicCustomData();
     const QVariantMap& publicCustomData() const;
     void setPublicCustomData(const QVariantMap& customData);
@@ -121,17 +121,17 @@ public:
     void emptyRecycleBin();
     void setEmitModified(bool value);
     void markAsModified();
-    QString saveToFile(QString filePath, bool atomic = true, bool backup = false);
+    QString saveToFile(const QString& filePath, bool atomic = true, bool backup = false);
 
     /**
      * Returns a unique id that is only valid as long as the Database exists.
      */
     const QUuid& uuid();
-    bool changeKdf(QSharedPointer<Kdf> kdf);
+    bool changeKdf(const QSharedPointer<Kdf>& kdf);
 
     static Database* databaseByUuid(const QUuid& uuid);
     static Database* openDatabaseFile(const QString& fileName, QSharedPointer<const CompositeKey> key);
-    static Database* unlockFromStdin(QString databaseFilename, QString keyFilename = {},
+    static Database* unlockFromStdin(const QString& databaseFilename, const QString& keyFilename = {},
         FILE* outputDescriptor = stdout, FILE* errorDescriptor = stderr);
 
 signals:
@@ -156,7 +156,7 @@ private:
 
     void createRecycleBin();
     QString writeDatabase(QIODevice* device);
-    bool backupDatabase(QString filePath);
+    bool backupDatabase(const QString& filePath);
 
     Metadata* const m_metadata;
     Group* m_rootGroup;
diff --git a/src/core/Entry.cpp b/src/core/Entry.cpp
index 6ce613d91..f6790da4b 100644
--- a/src/core/Entry.cpp
+++ b/src/core/Entry.cpp
@@ -29,6 +29,7 @@
 #include <QDebug>
 #include <QDir>
 #include <QRegularExpression>
+#include <utility>
 
 const int Entry::DefaultIconNumber = 0;
 const int Entry::ResolveMaximumDepth = 10;
@@ -367,7 +368,7 @@ QString Entry::totp() const
 void Entry::setTotp(QSharedPointer<Totp::Settings> settings)
 {
     beginUpdate();
-    m_data.totpSettings = settings;
+    m_data.totpSettings = std::move(settings);
 
     auto text = Totp::writeSettings(m_data.totpSettings, title(), username());
     if (m_attributes->hasKey(Totp::ATTRIBUTE_OTP)) {
diff --git a/src/core/EntrySearcher.cpp b/src/core/EntrySearcher.cpp
index 820646a98..3413f1cd0 100644
--- a/src/core/EntrySearcher.cpp
+++ b/src/core/EntrySearcher.cpp
@@ -34,12 +34,12 @@ EntrySearcher::searchEntries(const QString& searchTerm, const Group* group, Qt::
 {
     QList<Entry*> searchResult;
 
-    const QList<Entry*> entryList = group->entries();
+    const QList<Entry*>& entryList = group->entries();
     for (Entry* entry : entryList) {
         searchResult.append(matchEntry(searchTerm, entry, caseSensitivity));
     }
 
-    const QList<Group*> children = group->children();
+    const QList<Group*>& children = group->children();
     for (Group* childGroup : children) {
         if (childGroup->searchingEnabled() != Group::Disable) {
             if (matchGroup(searchTerm, childGroup, caseSensitivity)) {
diff --git a/src/core/Group.cpp b/src/core/Group.cpp
index dab48ebd1..fcb8fe8a8 100644
--- a/src/core/Group.cpp
+++ b/src/core/Group.cpp
@@ -563,7 +563,7 @@ Entry* Group::findEntryByUuid(const QUuid& uuid) const
     return nullptr;
 }
 
-Entry* Group::findEntryByPath(QString entryPath)
+Entry* Group::findEntryByPath(const QString& entryPath)
 {
     if (entryPath.isEmpty()) {
         return nullptr;
@@ -578,7 +578,7 @@ Entry* Group::findEntryByPath(QString entryPath)
     return findEntryByPathRecursive(normalizedEntryPath, "/");
 }
 
-Entry* Group::findEntryByPathRecursive(QString entryPath, QString basePath)
+Entry* Group::findEntryByPathRecursive(const QString& entryPath, const QString& basePath)
 {
     // Return the first entry that matches the full path OR if there is no leading
     // slash, return the first entry title that matches
@@ -599,7 +599,7 @@ Entry* Group::findEntryByPathRecursive(QString entryPath, QString basePath)
     return nullptr;
 }
 
-Group* Group::findGroupByPath(QString groupPath)
+Group* Group::findGroupByPath(const QString& groupPath)
 {
     // normalize the groupPath by adding missing front and rear slashes. once.
     QString normalizedGroupPath;
@@ -614,7 +614,7 @@ Group* Group::findGroupByPath(QString groupPath)
     return findGroupByPathRecursive(normalizedGroupPath, "/");
 }
 
-Group* Group::findGroupByPathRecursive(QString groupPath, QString basePath)
+Group* Group::findGroupByPathRecursive(const QString& groupPath, const QString& basePath)
 {
     // paths must be normalized
     Q_ASSERT(groupPath.startsWith("/") && groupPath.endsWith("/"));
@@ -811,7 +811,7 @@ void Group::removeEntry(Entry* entry)
 {
     Q_ASSERT_X(m_entries.contains(entry),
                Q_FUNC_INFO,
-               QString("Group %1 does not contain %2").arg(this->name()).arg(entry->title()).toLatin1());
+               QString("Group %1 does not contain %2").arg(this->name(), entry->title()).toLatin1());
 
     emit entryAboutToRemove(entry);
 
@@ -850,9 +850,9 @@ void Group::recSetDatabase(Database* db)
         connect(this, SIGNAL(dataChanged(Group*)), db, SIGNAL(groupDataChanged(Group*)));
         connect(this, SIGNAL(aboutToRemove(Group*)), db, SIGNAL(groupAboutToRemove(Group*)));
         connect(this, SIGNAL(removed()), db, SIGNAL(groupRemoved()));
-        connect(this, SIGNAL(aboutToAdd(Group*, int)), db, SIGNAL(groupAboutToAdd(Group*, int)));
+        connect(this, SIGNAL(aboutToAdd(Group*,int)), db, SIGNAL(groupAboutToAdd(Group*,int)));
         connect(this, SIGNAL(added()), db, SIGNAL(groupAdded()));
-        connect(this, SIGNAL(aboutToMove(Group*, Group*, int)), db, SIGNAL(groupAboutToMove(Group*, Group*, int)));
+        connect(this, SIGNAL(aboutToMove(Group*,Group*,int)), db, SIGNAL(groupAboutToMove(Group*,Group*,int)));
         connect(this, SIGNAL(moved()), db, SIGNAL(groupMoved()));
         connect(this, SIGNAL(modified()), db, SIGNAL(modifiedImmediate()));
     }
@@ -926,7 +926,7 @@ bool Group::resolveAutoTypeEnabled() const
     }
 }
 
-QStringList Group::locate(QString locateTerm, QString currentPath)
+QStringList Group::locate(const QString& locateTerm, const QString& currentPath) const
 {
     // TODO: Replace with EntrySearcher
     QStringList response;
@@ -934,15 +934,15 @@ QStringList Group::locate(QString locateTerm, QString currentPath)
         return response;
     }
 
-    for (Entry* entry : asConst(m_entries)) {
+    for (const Entry* entry : asConst(m_entries)) {
         QString entryPath = currentPath + entry->title();
         if (entryPath.toLower().contains(locateTerm.toLower())) {
             response << entryPath;
         }
     }
 
-    for (Group* group : asConst(m_children)) {
-        for (QString path : group->locate(locateTerm, currentPath + group->name() + QString("/"))) {
+    for (const Group* group : asConst(m_children)) {
+        for (const QString& path : group->locate(locateTerm, currentPath + group->name() + QString("/"))) {
             response << path;
         }
     }
@@ -950,7 +950,7 @@ QStringList Group::locate(QString locateTerm, QString currentPath)
     return response;
 }
 
-Entry* Group::addEntryWithPath(QString entryPath)
+Entry* Group::addEntryWithPath(const QString& entryPath)
 {
     if (entryPath.isEmpty() || findEntryByPath(entryPath)) {
         return nullptr;
diff --git a/src/core/Group.h b/src/core/Group.h
index e2b55cbd4..da6994d2a 100644
--- a/src/core/Group.h
+++ b/src/core/Group.h
@@ -115,11 +115,11 @@ public:
 
     Group* findChildByName(const QString& name);
     Entry* findEntryByUuid(const QUuid& uuid) const;
-    Entry* findEntryByPath(QString entryPath);
+    Entry* findEntryByPath(const QString& entryPath);
     Group* findGroupByUuid(const QUuid& uuid);
-    Group* findGroupByPath(QString groupPath);
-    QStringList locate(QString locateTerm, QString currentPath = {"/"});
-    Entry* addEntryWithPath(QString entryPath);
+    Group* findGroupByPath(const QString& groupPath);
+    QStringList locate(const QString& locateTerm, const QString& currentPath = {"/"}) const;
+    Entry* addEntryWithPath(const QString& entryPath);
     void setUuid(const QUuid& uuid);
     void setName(const QString& name);
     void setNotes(const QString& notes);
@@ -190,8 +190,8 @@ private:
     void cleanupParent();
     void recCreateDelObjects();
 
-    Entry* findEntryByPathRecursive(QString entryPath, QString basePath);
-    Group* findGroupByPathRecursive(QString groupPath, QString basePath);
+    Entry* findEntryByPathRecursive(const QString& entryPath, const QString& basePath);
+    Group* findGroupByPathRecursive(const QString& groupPath, const QString& basePath);
 
     QPointer<Database> m_db;
     QUuid m_uuid;
diff --git a/src/core/Merger.cpp b/src/core/Merger.cpp
index 9b87a6ac3..2bdff7377 100644
--- a/src/core/Merger.cpp
+++ b/src/core/Merger.cpp
@@ -95,7 +95,7 @@ Merger::ChangeList Merger::mergeGroup(const MergeContext& context)
             // Entry is already present in the database. Update it.
             const bool locationChanged = targetEntry->timeInfo().locationChanged() < sourceEntry->timeInfo().locationChanged();
             if (locationChanged && targetEntry->group() != context.m_targetGroup) {
-                changes << tr("Relocating %1 [%2]").arg(sourceEntry->title()).arg(sourceEntry->uuidToHex());
+                changes << tr("Relocating %1 [%2]").arg(sourceEntry->title(), sourceEntry->uuidToHex());
                 moveEntry(targetEntry, context.m_targetGroup);
             }
             changes << resolveEntryConflict(context, sourceEntry, targetEntry);
@@ -107,7 +107,7 @@ Merger::ChangeList Merger::mergeGroup(const MergeContext& context)
     for (Group* sourceChildGroup : sourceChildGroups) {
         Group* targetChildGroup = context.m_targetRootGroup->findGroupByUuid(sourceChildGroup->uuid());
         if (!targetChildGroup) {
-            changes << tr("Creating missing %1 [%2]").arg(sourceChildGroup->name()).arg(sourceChildGroup->uuidToHex());
+            changes << tr("Creating missing %1 [%2]").arg(sourceChildGroup->name(), sourceChildGroup->uuidToHex());
             targetChildGroup = sourceChildGroup->clone(Entry::CloneNoFlags, Group::CloneNoFlags);
             moveGroup(targetChildGroup, context.m_targetGroup);
             TimeInfo timeinfo = targetChildGroup->timeInfo();
@@ -117,7 +117,7 @@ Merger::ChangeList Merger::mergeGroup(const MergeContext& context)
             bool locationChanged =
                 targetChildGroup->timeInfo().locationChanged() < sourceChildGroup->timeInfo().locationChanged();
             if (locationChanged && targetChildGroup->parent() != context.m_targetGroup) {
-                changes << tr("Relocating %1 [%2]").arg(sourceChildGroup->name()).arg(sourceChildGroup->uuidToHex());
+                changes << tr("Relocating %1 [%2]").arg(sourceChildGroup->name(), sourceChildGroup->uuidToHex());
                 moveGroup(targetChildGroup, context.m_targetGroup);
                 TimeInfo timeinfo = targetChildGroup->timeInfo();
                 timeinfo.setLocationChanged(sourceChildGroup->timeInfo().locationChanged());
@@ -146,7 +146,7 @@ Merger::ChangeList Merger::resolveGroupConflict(const MergeContext& context, con
 
     // only if the other group is newer, update the existing one.
     if (timeExisting < timeOther) {
-        changes << tr("Overwriting %1 [%2]").arg(sourceChildGroup->name()).arg(sourceChildGroup->uuidToHex());
+        changes << tr("Overwriting %1 [%2]").arg(sourceChildGroup->name(), sourceChildGroup->uuidToHex());
         targetChildGroup->setName(sourceChildGroup->name());
         targetChildGroup->setNotes(sourceChildGroup->notes());
         if (sourceChildGroup->iconNumber() == 0) {
@@ -270,16 +270,12 @@ Merger::ChangeList Merger::resolveEntryConflict_Duplicate(const MergeContext& co
         Entry* clonedEntry = sourceEntry->clone(Entry::CloneNewUuid | Entry::CloneIncludeHistory);
         moveEntry(clonedEntry, context.m_targetGroup);
         markOlderEntry(targetEntry);
-        changes << tr("Adding backup for older target %1 [%2]")
-                   .arg(targetEntry->title())
-                   .arg(targetEntry->uuidToHex());
+        changes << tr("Adding backup for older target %1 [%2]").arg(targetEntry->title(), targetEntry->uuidToHex());
     } else if (comparison > 0) {
         Entry* clonedEntry = sourceEntry->clone(Entry::CloneNewUuid | Entry::CloneIncludeHistory);
         moveEntry(clonedEntry, context.m_targetGroup);
         markOlderEntry(clonedEntry);
-        changes << tr("Adding backup for older source %1 [%2]")
-                   .arg(sourceEntry->title())
-                   .arg(sourceEntry->uuidToHex());
+        changes << tr("Adding backup for older source %1 [%2]").arg(sourceEntry->title(), sourceEntry->uuidToHex());
     }
     return changes;
 }
@@ -297,8 +293,7 @@ Merger::ChangeList Merger::resolveEntryConflict_KeepLocal(const MergeContext& co
         // this type of merge changes the database timestamp since reapplying the
         // old entry is an active change of the database!
         changes << tr("Reapplying older target entry on top of newer source %1 [%2]")
-                   .arg(targetEntry->title())
-                   .arg(targetEntry->uuidToHex());
+                   .arg(targetEntry->title(), targetEntry->uuidToHex());
         Entry* agedTargetEntry = targetEntry->clone(Entry::CloneNoFlags);
         targetEntry->addHistoryItem(agedTargetEntry);
     }
@@ -318,8 +313,7 @@ Merger::ChangeList Merger::resolveEntryConflict_KeepRemote(const MergeContext& c
         // this type of merge changes the database timestamp since reapplying the
         // old entry is an active change of the database!
         changes << tr("Reapplying older source entry on top of newer target %1 [%2]")
-                   .arg(targetEntry->title())
-                   .arg(targetEntry->uuidToHex());
+                   .arg(targetEntry->title(), targetEntry->uuidToHex());
         targetEntry->beginUpdate();
         targetEntry->copyDataFrom(sourceEntry);
         targetEntry->endUpdate();
@@ -342,9 +336,7 @@ Merger::ChangeList Merger::resolveEntryConflict_MergeHistories(const MergeContex
                qPrintable(targetEntry->title()),
                qPrintable(sourceEntry->title()),
                qPrintable(currentGroup->name()));
-        changes << tr("Synchronizing from newer source %1 [%2]")
-                   .arg(targetEntry->title())
-                   .arg(targetEntry->uuidToHex());
+        changes << tr("Synchronizing from newer source %1 [%2]").arg(targetEntry->title(), targetEntry->uuidToHex());
         moveEntry(clonedEntry, currentGroup);
         mergeHistory(targetEntry, clonedEntry, mergeMethod);
         eraseEntry(targetEntry);
@@ -355,9 +347,7 @@ Merger::ChangeList Merger::resolveEntryConflict_MergeHistories(const MergeContex
                qPrintable(targetEntry->group()->name()));
         const bool changed = mergeHistory(sourceEntry, targetEntry, mergeMethod);
         if (changed) {
-            changes << tr("Synchronizing from older source %1 [%2]")
-                       .arg(targetEntry->title())
-                       .arg(targetEntry->uuidToHex());
+            changes << tr("Synchronizing from older source %1 [%2]").arg(targetEntry->title(), targetEntry->uuidToHex());
         }
     }
     return changes;
@@ -550,9 +540,9 @@ Merger::ChangeList Merger::mergeDeletions(const MergeContext& context)
         }
         deletions << object;
         if (entry->group()) {
-            changes << tr("Deleting child %1 [%2]").arg(entry->title()).arg(entry->uuidToHex());
+            changes << tr("Deleting child %1 [%2]").arg(entry->title(), entry->uuidToHex());
         } else {
-            changes << tr("Deleting orphan %1 [%2]").arg(entry->title()).arg(entry->uuidToHex());
+            changes << tr("Deleting orphan %1 [%2]").arg(entry->title(), entry->uuidToHex());
         }
         // Entry is inserted into deletedObjects after deletions are processed
         eraseEntry(entry);
@@ -576,9 +566,9 @@ Merger::ChangeList Merger::mergeDeletions(const MergeContext& context)
         }
         deletions << object;
         if (group->parentGroup()) {
-            changes << tr("Deleting child %1 [%2]").arg(group->name()).arg(group->uuidToHex());
+            changes << tr("Deleting child %1 [%2]").arg(group->name(), group->uuidToHex());
         } else {
-            changes << tr("Deleting orphan %1 [%2]").arg(group->name()).arg(group->uuidToHex());
+            changes << tr("Deleting orphan %1 [%2]").arg(group->name(), group->uuidToHex());
         }
         eraseGroup(group);
     }
diff --git a/src/core/PasswordGenerator.cpp b/src/core/PasswordGenerator.cpp
index 3dbcdaad8..69a0dfb3e 100644
--- a/src/core/PasswordGenerator.cpp
+++ b/src/core/PasswordGenerator.cpp
@@ -25,15 +25,15 @@ const char* PasswordGenerator::DefaultExcludedChars = "";
 
 PasswordGenerator::PasswordGenerator()
     : m_length(0)
-    , m_classes(0)
-    , m_flags(0)
+    , m_classes(nullptr)
+    , m_flags(nullptr)
     , m_excluded(PasswordGenerator::DefaultExcludedChars)
 {
 }
 
-double PasswordGenerator::calculateEntropy(QString password)
+double PasswordGenerator::calculateEntropy(const QString& password)
 {
-    return ZxcvbnMatch(password.toLatin1(), 0, 0);
+    return ZxcvbnMatch(password.toLatin1(), nullptr, nullptr);
 }
 
 void PasswordGenerator::setLength(int length)
diff --git a/src/core/PasswordGenerator.h b/src/core/PasswordGenerator.h
index cb6402d0f..7bfdddd69 100644
--- a/src/core/PasswordGenerator.h
+++ b/src/core/PasswordGenerator.h
@@ -57,7 +57,7 @@ public:
 public:
     PasswordGenerator();
 
-    double calculateEntropy(QString password);
+    double calculateEntropy(const QString& password);
     void setLength(int length);
     void setCharClasses(const CharClasses& classes);
     void setFlags(const GeneratorFlags& flags);
diff --git a/src/core/ScreenLockListenerPrivate.h b/src/core/ScreenLockListenerPrivate.h
index 8ecad17d8..a7c080687 100644
--- a/src/core/ScreenLockListenerPrivate.h
+++ b/src/core/ScreenLockListenerPrivate.h
@@ -24,10 +24,10 @@ class ScreenLockListenerPrivate : public QObject
 {
     Q_OBJECT
 public:
-    static ScreenLockListenerPrivate* instance(QWidget* parent = 0);
+    static ScreenLockListenerPrivate* instance(QWidget* parent = nullptr);
 
 protected:
-    ScreenLockListenerPrivate(QWidget* parent = 0);
+    ScreenLockListenerPrivate(QWidget* parent = nullptr);
 
 signals:
     void screenLocked();
diff --git a/src/core/ScreenLockListenerWin.h b/src/core/ScreenLockListenerWin.h
index 0778c99d8..523ae5d0b 100644
--- a/src/core/ScreenLockListenerWin.h
+++ b/src/core/ScreenLockListenerWin.h
@@ -27,7 +27,7 @@ class ScreenLockListenerWin : public ScreenLockListenerPrivate, public QAbstract
 {
     Q_OBJECT
 public:
-    explicit ScreenLockListenerWin(QWidget* parent = 0);
+    explicit ScreenLockListenerWin(QWidget* parent = nullptr);
     ~ScreenLockListenerWin();
     virtual bool nativeEventFilter(const QByteArray& eventType, void* message, long*) override;
 
diff --git a/src/core/Tools.cpp b/src/core/Tools.cpp
index 8467fb416..ded3a1651 100644
--- a/src/core/Tools.cpp
+++ b/src/core/Tools.cpp
@@ -121,8 +121,8 @@ QString imageReaderFilter()
     QStringList formatsStringList;
 
     for (const QByteArray& format : formats) {
-        for (int i = 0; i < format.size(); i++) {
-            if (!QChar(format.at(i)).isLetterOrNumber()) {
+        for (char codePoint : format) {
+            if (!QChar(codePoint).isLetterOrNumber()) {
                 continue;
             }
         }
diff --git a/src/crypto/Crypto.cpp b/src/crypto/Crypto.cpp
index 0ed6f003a..fffcddfbd 100644
--- a/src/crypto/Crypto.cpp
+++ b/src/crypto/Crypto.cpp
@@ -336,4 +336,4 @@ bool Crypto::testChaCha20()
     }
 
     return true;
-}
\ No newline at end of file
+}
diff --git a/src/format/CsvExporter.cpp b/src/format/CsvExporter.cpp
index c444afe23..67e6a44fc 100644
--- a/src/format/CsvExporter.cpp
+++ b/src/format/CsvExporter.cpp
@@ -64,7 +64,7 @@ bool CsvExporter::writeGroup(QIODevice* device, const Group* group, QString grou
     }
     groupPath.append(group->name());
 
-    const QList<Entry*> entryList = group->entries();
+    const QList<Entry*>& entryList = group->entries();
     for (const Entry* entry : entryList) {
         QString line;
 
@@ -83,7 +83,7 @@ bool CsvExporter::writeGroup(QIODevice* device, const Group* group, QString grou
         }
     }
 
-    const QList<Group*> children = group->children();
+    const QList<Group*>& children = group->children();
     for (const Group* child : children) {
         if (!writeGroup(device, child, groupPath)) {
             return false;
diff --git a/src/format/KdbxXmlReader.cpp b/src/format/KdbxXmlReader.cpp
index c9e5c31af..ec556dd85 100644
--- a/src/format/KdbxXmlReader.cpp
+++ b/src/format/KdbxXmlReader.cpp
@@ -28,6 +28,7 @@
 
 #include <QBuffer>
 #include <QFile>
+#include <utility>
 
 #define UUID_LENGTH 16
 
@@ -43,9 +44,9 @@ KdbxXmlReader::KdbxXmlReader(quint32 version)
  * @param version KDBX version
  * @param binaryPool binary pool
  */
-KdbxXmlReader::KdbxXmlReader(quint32 version, const QHash<QString, QByteArray>& binaryPool)
+KdbxXmlReader::KdbxXmlReader(quint32 version, QHash<QString, QByteArray>  binaryPool)
     : m_kdbxVersion(version)
-    , m_binaryPool(binaryPool)
+    , m_binaryPool(std::move(binaryPool))
 {
 }
 
diff --git a/src/format/KdbxXmlReader.h b/src/format/KdbxXmlReader.h
index 566fbfc7e..4ab82cc0e 100644
--- a/src/format/KdbxXmlReader.h
+++ b/src/format/KdbxXmlReader.h
@@ -42,7 +42,7 @@ class KdbxXmlReader
 
 public:
     explicit KdbxXmlReader(quint32 version);
-    explicit KdbxXmlReader(quint32 version, const QHash<QString, QByteArray>& binaryPool);
+    explicit KdbxXmlReader(quint32 version, QHash<QString, QByteArray>  binaryPool);
     virtual ~KdbxXmlReader() = default;
 
     virtual Database* readDatabase(const QString& filename);
diff --git a/src/format/KeePass1Reader.cpp b/src/format/KeePass1Reader.cpp
index 7c0ea652e..a991b572f 100644
--- a/src/format/KeePass1Reader.cpp
+++ b/src/format/KeePass1Reader.cpp
@@ -37,7 +37,7 @@
 class KeePass1Key : public CompositeKey
 {
 public:
-    virtual QByteArray rawKey() const;
+    QByteArray rawKey() const override;
     virtual void clear();
     void setPassword(const QByteArray& password);
     void setKeyfileData(const QByteArray& keyfileData);
diff --git a/src/format/KeePass2.cpp b/src/format/KeePass2.cpp
index 9c0714484..639255d27 100644
--- a/src/format/KeePass2.cpp
+++ b/src/format/KeePass2.cpp
@@ -59,7 +59,7 @@ const QList<QPair<QUuid, QString>> KeePass2::KDFS{
     qMakePair(KeePass2::KDF_AES_KDBX3, QObject::tr("AES-KDF (KDBX 3.1)"))
 };
 
-QByteArray KeePass2::hmacKey(QByteArray masterSeed, QByteArray transformedMasterKey)
+QByteArray KeePass2::hmacKey(const QByteArray& masterSeed, const QByteArray& transformedMasterKey)
 {
     CryptoHash hmacKeyHash(CryptoHash::Sha512);
     hmacKeyHash.addData(masterSeed);
@@ -98,7 +98,7 @@ QSharedPointer<Kdf> KeePass2::kdfFromParameters(const QVariantMap& p)
     return kdf;
 }
 
-QVariantMap KeePass2::kdfToParameters(QSharedPointer<Kdf> kdf)
+QVariantMap KeePass2::kdfToParameters(const QSharedPointer<Kdf>& kdf)
 {
     return kdf->writeParameters();
 }
diff --git a/src/format/KeePass2.h b/src/format/KeePass2.h
index 02fe635ca..195ce8c2b 100644
--- a/src/format/KeePass2.h
+++ b/src/format/KeePass2.h
@@ -126,9 +126,9 @@ extern const QList<QPair<QUuid, QString>> KDFS;
         ByteArray = 0x42
     };
 
-QByteArray hmacKey(QByteArray masterSeed, QByteArray transformedMasterKey);
+QByteArray hmacKey(const QByteArray& masterSeed, const QByteArray& transformedMasterKey);
 QSharedPointer<Kdf> kdfFromParameters(const QVariantMap& p);
-QVariantMap kdfToParameters(QSharedPointer<Kdf> kdf);
+QVariantMap kdfToParameters(const QSharedPointer<Kdf>& kdf);
 QSharedPointer<Kdf> uuidToKdf(const QUuid& uuid);
 ProtectedStreamAlgo idToProtectedStreamAlgo(quint32 id);
 
diff --git a/src/format/KeePass2Reader.cpp b/src/format/KeePass2Reader.cpp
index 8cdb8ff43..f727f274d 100644
--- a/src/format/KeePass2Reader.cpp
+++ b/src/format/KeePass2Reader.cpp
@@ -21,6 +21,7 @@
 #include "format/KeePass1.h"
 
 #include <QFile>
+#include <utility>
 
 /**
  * Read database from file and detect correct file format.
@@ -37,7 +38,7 @@ Database* KeePass2Reader::readDatabase(const QString& filename, QSharedPointer<c
         return nullptr;
     }
 
-    QScopedPointer<Database> db(readDatabase(&file, key));
+    QScopedPointer<Database> db(readDatabase(&file, std::move(key)));
 
     if (file.error() != QFile::NoError) {
         raiseError(file.errorString());
diff --git a/src/gui/AboutDialog.cpp b/src/gui/AboutDialog.cpp
index f6a9d15f9..483e4dd2b 100644
--- a/src/gui/AboutDialog.cpp
+++ b/src/gui/AboutDialog.cpp
@@ -65,9 +65,9 @@ AboutDialog::AboutDialog(QWidget* parent)
 #endif
 
     debugInfo.append("\n").append(QString("%1\n- Qt %2\n- %3\n\n")
-                                      .arg(tr("Libraries:"))
-                                      .arg(QString::fromLocal8Bit(qVersion()))
-                                      .arg(Crypto::backendVersion()));
+                                      .arg(tr("Libraries:"),
+                                           QString::fromLocal8Bit(qVersion()),
+                                           Crypto::backendVersion()));
 
 #if QT_VERSION >= QT_VERSION_CHECK(5, 4, 0)
     debugInfo.append(tr("Operating system: %1\nCPU architecture: %2\nKernel: %3 %4")
diff --git a/src/gui/ApplicationSettingsWidget.cpp b/src/gui/ApplicationSettingsWidget.cpp
index c23e2bfa5..a0293ce8d 100644
--- a/src/gui/ApplicationSettingsWidget.cpp
+++ b/src/gui/ApplicationSettingsWidget.cpp
@@ -146,8 +146,8 @@ void ApplicationSettingsWidget::loadSettings()
 
     m_generalUi->languageComboBox->clear();
     QList<QPair<QString, QString>> languages = Translator::availableLanguages();
-    for (int i = 0; i < languages.size(); i++) {
-        m_generalUi->languageComboBox->addItem(languages[i].second, languages[i].first);
+    for (const auto& language : languages) {
+        m_generalUi->languageComboBox->addItem(language.second, language.first);
     }
     int defaultIndex = m_generalUi->languageComboBox->findData(config()->get("GUI/Language"));
     if (defaultIndex > 0) {
diff --git a/src/gui/CategoryListWidget.cpp b/src/gui/CategoryListWidget.cpp
index 14429083b..50b02da81 100644
--- a/src/gui/CategoryListWidget.cpp
+++ b/src/gui/CategoryListWidget.cpp
@@ -39,7 +39,7 @@ CategoryListWidget::CategoryListWidget(QWidget* parent)
     connect(m_ui->scrollDown, SIGNAL(clicked()), SLOT(scrollCategoriesDown()));
     connect(m_ui->categoryList->verticalScrollBar(), SIGNAL(valueChanged(int)), SLOT(updateCategoryScrollButtons()));
     connect(
-        m_ui->categoryList->verticalScrollBar(), SIGNAL(rangeChanged(int, int)), SLOT(updateCategoryScrollButtons()));
+        m_ui->categoryList->verticalScrollBar(), SIGNAL(rangeChanged(int,int)), SLOT(updateCategoryScrollButtons()));
 }
 
 CategoryListWidget::~CategoryListWidget()
diff --git a/src/gui/CategoryListWidget.h b/src/gui/CategoryListWidget.h
index 3f08fe384..7873a3d3e 100644
--- a/src/gui/CategoryListWidget.h
+++ b/src/gui/CategoryListWidget.h
@@ -35,7 +35,7 @@ class CategoryListWidget : public QWidget
     Q_OBJECT
 
 public:
-    CategoryListWidget(QWidget* parent = 0);
+    CategoryListWidget(QWidget* parent = nullptr);
     ~CategoryListWidget();
 
     int currentCategory();
@@ -90,4 +90,4 @@ private:
     Q_DISABLE_COPY(CategoryListWidgetDelegate)
 };
 
-#endif
\ No newline at end of file
+#endif
diff --git a/src/gui/DatabaseOpenWidget.cpp b/src/gui/DatabaseOpenWidget.cpp
index 67af3ff13..d872ca68d 100644
--- a/src/gui/DatabaseOpenWidget.cpp
+++ b/src/gui/DatabaseOpenWidget.cpp
@@ -106,7 +106,7 @@ void DatabaseOpenWidget::showEvent(QShowEvent* event)
     // showEvent() may be called twice, so make sure we are only polling once
     if (!m_yubiKeyBeingPolled) {
         connect(
-            YubiKey::instance(), SIGNAL(detected(int, bool)), SLOT(yubikeyDetected(int, bool)), Qt::QueuedConnection);
+            YubiKey::instance(), SIGNAL(detected(int,bool)), SLOT(yubikeyDetected(int,bool)), Qt::QueuedConnection);
         connect(YubiKey::instance(), SIGNAL(detectComplete()), SLOT(yubikeyDetectComplete()), Qt::QueuedConnection);
         connect(YubiKey::instance(), SIGNAL(notFound()), SLOT(noYubikeyFound()), Qt::QueuedConnection);
 
@@ -122,7 +122,7 @@ void DatabaseOpenWidget::hideEvent(QHideEvent* event)
 
 #ifdef WITH_XC_YUBIKEY
     // Don't listen to any Yubikey events if we are hidden
-    disconnect(YubiKey::instance(), 0, this, 0);
+    disconnect(YubiKey::instance(), nullptr, this, nullptr);
     m_yubiKeyBeingPolled = false;
 #endif
 }
@@ -143,7 +143,7 @@ void DatabaseOpenWidget::load(const QString& filename)
 
     QHash<QString, QVariant> useTouchID = config()->get("UseTouchID").toHash();
     m_ui->checkTouchID->setChecked(useTouchID.value(m_filename, false).toBool());
-    
+
     m_ui->editPassword->setFocus();
 }
 
@@ -195,9 +195,9 @@ void DatabaseOpenWidget::openDatabase()
                                          MessageWidget::Error);
         return;
     }
-    if (m_db) {
-        delete m_db;
-    }
+
+    delete m_db;
+
     QApplication::setOverrideCursor(QCursor(Qt::WaitCursor));
     m_db = reader.readDatabase(&file, masterKey);
     QApplication::restoreOverrideCursor();
@@ -254,7 +254,7 @@ QSharedPointer<CompositeKey> DatabaseOpenWidget::databaseKey()
             // check if the user cancelled the operation
             if (passwordKey.isNull())
                 return QSharedPointer<CompositeKey>();
-            
+
             masterKey->addKey(PasswordKey::fromRawKey(*passwordKey));
         }
     }
diff --git a/src/gui/DatabaseTabWidget.cpp b/src/gui/DatabaseTabWidget.cpp
index dd36ddae4..fcd4f954b 100644
--- a/src/gui/DatabaseTabWidget.cpp
+++ b/src/gui/DatabaseTabWidget.cpp
@@ -419,7 +419,7 @@ bool DatabaseTabWidget::saveDatabaseAs(Database* db)
                                                             oldFilePath,
                                                             tr("KeePass 2 Database").append(" (*.kdbx)"),
                                                             nullptr,
-                                                            0,
+                                                            nullptr,
                                                             "kdbx");
         if (!newFilePath.isEmpty()) {
             // Ensure we don't recurse back into this function
@@ -488,7 +488,7 @@ void DatabaseTabWidget::exportToCsv()
     }
 
     QString fileName = fileDialog()->getSaveFileName(
-        this, tr("Export database to CSV file"), QString(), tr("CSV file").append(" (*.csv)"), nullptr, 0, "csv");
+        this, tr("Export database to CSV file"), QString(), tr("CSV file").append(" (*.csv)"), nullptr, nullptr, "csv");
     if (fileName.isEmpty()) {
         return;
     }
@@ -693,7 +693,7 @@ void DatabaseTabWidget::insertDatabase(Database* db, const DatabaseManagerStruct
     setCurrentIndex(index);
     connectDatabase(db);
     connect(dbStruct.dbWidget, SIGNAL(closeRequest()), SLOT(closeDatabaseFromSender()));
-    connect(dbStruct.dbWidget, SIGNAL(databaseChanged(Database*, bool)), SLOT(changeDatabase(Database*, bool)));
+    connect(dbStruct.dbWidget, SIGNAL(databaseChanged(Database*,bool)), SLOT(changeDatabase(Database*,bool)));
     connect(dbStruct.dbWidget, SIGNAL(unlockedDatabase()), SLOT(updateTabNameFromDbWidgetSender()));
     connect(dbStruct.dbWidget, SIGNAL(unlockedDatabase()), SLOT(emitDatabaseUnlockedFromDbWidgetSender()));
 }
diff --git a/src/gui/DatabaseWidget.cpp b/src/gui/DatabaseWidget.cpp
index 7b36f4668..388919952 100644
--- a/src/gui/DatabaseWidget.cpp
+++ b/src/gui/DatabaseWidget.cpp
@@ -175,14 +175,14 @@ DatabaseWidget::DatabaseWidget(Database* db, QWidget* parent)
     addWidget(m_keepass1OpenWidget);
     addWidget(m_unlockDatabaseWidget);
 
-    connect(m_mainSplitter, SIGNAL(splitterMoved(int, int)), SIGNAL(mainSplitterSizesChanged()));
-    connect(m_previewSplitter, SIGNAL(splitterMoved(int, int)), SIGNAL(previewSplitterSizesChanged()));
+    connect(m_mainSplitter, SIGNAL(splitterMoved(int,int)), SIGNAL(mainSplitterSizesChanged()));
+    connect(m_previewSplitter, SIGNAL(splitterMoved(int,int)), SIGNAL(previewSplitterSizesChanged()));
     connect(m_entryView, SIGNAL(viewStateChanged()), SIGNAL(entryViewStateChanged()));
     connect(m_groupView, SIGNAL(groupChanged(Group*)), this, SLOT(onGroupChanged(Group*)));
     connect(m_groupView, SIGNAL(groupChanged(Group*)), SIGNAL(groupChanged()));
     connect(m_entryView,
-            SIGNAL(entryActivated(Entry*, EntryModel::ModelColumn)),
-            SLOT(entryActivationSignalReceived(Entry*, EntryModel::ModelColumn)));
+            SIGNAL(entryActivated(Entry*,EntryModel::ModelColumn)),
+            SLOT(entryActivationSignalReceived(Entry*,EntryModel::ModelColumn)));
     connect(m_entryView, SIGNAL(entrySelectionChanged()), SIGNAL(entrySelectionChanged()));
     connect(m_editEntryWidget, SIGNAL(editFinished(bool)), SLOT(switchToView(bool)));
     connect(m_editEntryWidget, SIGNAL(historyEntryActivated(Entry*)), SLOT(switchToHistoryView(Entry*)));
diff --git a/src/gui/DialogyWidget.cpp b/src/gui/DialogyWidget.cpp
index 89e114f10..858d2949b 100644
--- a/src/gui/DialogyWidget.cpp
+++ b/src/gui/DialogyWidget.cpp
@@ -71,8 +71,7 @@ bool DialogyWidget::clickButton(QDialogButtonBox::StandardButton standardButton)
     }
 
     QList<QDialogButtonBox*> buttonBoxes = findChildren<QDialogButtonBox*>();
-    for (int i = 0; i < buttonBoxes.size(); ++i) {
-        QDialogButtonBox* buttonBox = buttonBoxes.at(i);
+    for (auto buttonBox : buttonBoxes) {
         pb = buttonBox->button(standardButton);
         if (pb && pb->isVisible() && pb->isEnabled()) {
             pb->click();
diff --git a/src/gui/EditWidgetIcons.cpp b/src/gui/EditWidgetIcons.cpp
index 0555359d8..e26966df6 100644
--- a/src/gui/EditWidgetIcons.cpp
+++ b/src/gui/EditWidgetIcons.cpp
@@ -84,11 +84,11 @@ EditWidgetIcons::EditWidgetIcons(QWidget* parent)
     connect(m_ui->defaultIconsRadio, SIGNAL(toggled(bool)), this, SIGNAL(widgetUpdated()));
     connect(m_ui->defaultIconsRadio, SIGNAL(toggled(bool)), this, SIGNAL(widgetUpdated()));
     connect(m_ui->defaultIconsView->selectionModel(),
-            SIGNAL(selectionChanged(const QItemSelection&, const QItemSelection&)),
+            SIGNAL(selectionChanged(QItemSelection,QItemSelection)),
             this,
             SIGNAL(widgetUpdated()));
     connect(m_ui->customIconsView->selectionModel(),
-            SIGNAL(selectionChanged(const QItemSelection&, const QItemSelection&)),
+            SIGNAL(selectionChanged(QItemSelection,QItemSelection)),
             this,
             SIGNAL(widgetUpdated()));
 
@@ -176,7 +176,7 @@ namespace {
     // Try to get the 2nd level domain of the host part of a QUrl. For example,
     // "foo.bar.example.com" would become "example.com", and "foo.bar.example.co.uk"
     // would become "example.co.uk".
-    QString getSecondLevelDomain(QUrl url)
+    QString getSecondLevelDomain(const QUrl& url)
     {
         QString fqdn = url.host();
         fqdn.truncate(fqdn.length() - url.topLevelDomain().length());
@@ -185,7 +185,7 @@ namespace {
         return newdom;
     }
 
-    QUrl convertVariantToUrl(QVariant var)
+    QUrl convertVariantToUrl(const QVariant& var)
     {
         QUrl url;
         if (var.canConvert<QUrl>())
diff --git a/src/gui/EditWidgetProperties.cpp b/src/gui/EditWidgetProperties.cpp
index 93e3b0ae8..b2de9d778 100644
--- a/src/gui/EditWidgetProperties.cpp
+++ b/src/gui/EditWidgetProperties.cpp
@@ -33,7 +33,7 @@ EditWidgetProperties::EditWidgetProperties(QWidget* parent)
     m_ui->customDataTable->setModel(m_customDataModel);
 
     connect(m_ui->customDataTable->selectionModel(),
-            SIGNAL(selectionChanged(QItemSelection, QItemSelection)),
+            SIGNAL(selectionChanged(QItemSelection,QItemSelection)),
             SLOT(toggleRemoveButton(QItemSelection)));
     connect(m_ui->removeCustomDataButton, SIGNAL(clicked()), SLOT(removeSelectedPluginData()));
 }
diff --git a/src/gui/FileDialog.cpp b/src/gui/FileDialog.cpp
index 5bccc4af3..b063d62f3 100644
--- a/src/gui/FileDialog.cpp
+++ b/src/gui/FileDialog.cpp
@@ -178,7 +178,7 @@ FileDialog::FileDialog()
 {
 }
 
-void FileDialog::saveLastDir(QString dir)
+void FileDialog::saveLastDir(const QString& dir)
 {
     if (!dir.isEmpty() && !m_forgetLastDir) {
         config()->set("LastDir", QFileInfo(dir).absolutePath());
diff --git a/src/gui/FileDialog.h b/src/gui/FileDialog.h
index 4862dcfda..83b151ec9 100644
--- a/src/gui/FileDialog.h
+++ b/src/gui/FileDialog.h
@@ -65,7 +65,7 @@ private:
     QString m_nextDirName;
     bool m_forgetLastDir = false;
 
-    void saveLastDir(QString);
+    void saveLastDir(const QString&);
 
     static FileDialog* m_instance;
 
diff --git a/src/gui/KMessageWidget.cpp b/src/gui/KMessageWidget.cpp
index 3d0500708..3de1a15b6 100644
--- a/src/gui/KMessageWidget.cpp
+++ b/src/gui/KMessageWidget.cpp
@@ -309,10 +309,10 @@ void KMessageWidget::setMessageType(KMessageWidget::MessageType type)
         "}"
         ".QLabel { color: %6; }"
         ))
-        .arg(bg0.name())
-        .arg(bg1.name())
-        .arg(bg2.name())
-        .arg(border.name())
+        .arg(bg0.name(),
+             bg1.name(),
+             bg2.name(),
+             border.name())
         // DefaultFrameWidth returns the size of the external margin + border width. We know our border is 1px,
         // so we subtract this from the frame normal QStyle FrameWidth to get our margin
         .arg(style()->pixelMetric(QStyle::PM_DefaultFrameWidth, nullptr, this) - 1)
@@ -411,7 +411,7 @@ void KMessageWidget::removeAction(QAction *action)
 
 void KMessageWidget::animatedShow()
 {
-    if (!style()->styleHint(QStyle::SH_Widget_Animate, 0, this)) {
+    if (!style()->styleHint(QStyle::SH_Widget_Animate, nullptr, this)) {
         show();
         emit showAnimationFinished();
         return;
@@ -436,7 +436,7 @@ void KMessageWidget::animatedShow()
 
 void KMessageWidget::animatedHide()
 {
-    if (!style()->styleHint(QStyle::SH_Widget_Animate, 0, this)) {
+    if (!style()->styleHint(QStyle::SH_Widget_Animate, nullptr, this)) {
         hide();
         emit hideAnimationFinished();
         return;
diff --git a/src/gui/KeePass1OpenWidget.cpp b/src/gui/KeePass1OpenWidget.cpp
index 4a54aaf3a..8123d239f 100644
--- a/src/gui/KeePass1OpenWidget.cpp
+++ b/src/gui/KeePass1OpenWidget.cpp
@@ -53,9 +53,9 @@ void KeePass1OpenWidget::openDatabase()
                                          MessageWidget::Error);
         return;
     }
-    if (m_db) {
-        delete m_db;
-    }
+
+    delete m_db;
+
     QApplication::setOverrideCursor(QCursor(Qt::WaitCursor));
     m_db = reader.readDatabase(&file, password, keyFileName);
     QApplication::restoreOverrideCursor();
diff --git a/src/gui/MainWindow.cpp b/src/gui/MainWindow.cpp
index 9efe0c273..ac26dd879 100644
--- a/src/gui/MainWindow.cpp
+++ b/src/gui/MainWindow.cpp
@@ -319,14 +319,14 @@ MainWindow::MainWindow()
 #endif
 
     connect(m_ui->tabWidget,
-            SIGNAL(messageGlobal(QString, MessageWidget::MessageType)),
+            SIGNAL(messageGlobal(QString,MessageWidget::MessageType)),
             this,
-            SLOT(displayGlobalMessage(QString, MessageWidget::MessageType)));
+            SLOT(displayGlobalMessage(QString,MessageWidget::MessageType)));
     connect(m_ui->tabWidget, SIGNAL(messageDismissGlobal()), this, SLOT(hideGlobalMessage()));
     connect(m_ui->tabWidget,
-            SIGNAL(messageTab(QString, MessageWidget::MessageType)),
+            SIGNAL(messageTab(QString,MessageWidget::MessageType)),
             this,
-            SLOT(displayTabMessage(QString, MessageWidget::MessageType)));
+            SLOT(displayTabMessage(QString,MessageWidget::MessageType)));
     connect(m_ui->tabWidget, SIGNAL(messageDismissTab()), this, SLOT(hideTabMessage()));
 
     m_screenLockListener = new ScreenLockListener(this);
@@ -673,7 +673,7 @@ void MainWindow::switchToOpenDatabase()
     switchToDatabases();
 }
 
-void MainWindow::switchToDatabaseFile(QString file)
+void MainWindow::switchToDatabaseFile(const QString& file)
 {
     m_ui->tabWidget->openDatabase(file);
     switchToDatabases();
diff --git a/src/gui/MainWindow.h b/src/gui/MainWindow.h
index d83b4a1ff..174e47564 100644
--- a/src/gui/MainWindow.h
+++ b/src/gui/MainWindow.h
@@ -90,7 +90,7 @@ private slots:
     void switchToPasswordGen(bool enabled);
     void switchToNewDatabase();
     void switchToOpenDatabase();
-    void switchToDatabaseFile(QString file);
+    void switchToDatabaseFile(const QString& file);
     void switchToKeePass1Database();
     void switchToCsvImport();
     void closePasswordGen();
diff --git a/src/gui/MessageWidget.h b/src/gui/MessageWidget.h
index 73f0b2108..eac506014 100644
--- a/src/gui/MessageWidget.h
+++ b/src/gui/MessageWidget.h
@@ -28,7 +28,7 @@ class MessageWidget : public KMessageWidget
     Q_OBJECT
 
 public:
-    explicit MessageWidget(QWidget* parent = 0);
+    explicit MessageWidget(QWidget* parent = nullptr);
 
     int autoHideTimeout() const;
 
diff --git a/src/gui/PasswordEdit.cpp b/src/gui/PasswordEdit.cpp
index 33d022176..02067ccc4 100644
--- a/src/gui/PasswordEdit.cpp
+++ b/src/gui/PasswordEdit.cpp
@@ -98,7 +98,7 @@ void PasswordEdit::updateStylesheet()
     setStyleSheet(stylesheet);
 }
 
-void PasswordEdit::autocompletePassword(QString password)
+void PasswordEdit::autocompletePassword(const QString& password)
 {
     if (config()->get("security/passwordsrepeat").toBool() && echoMode() == QLineEdit::Normal) {
         setText(password);
diff --git a/src/gui/PasswordEdit.h b/src/gui/PasswordEdit.h
index 5976347e6..222376d09 100644
--- a/src/gui/PasswordEdit.h
+++ b/src/gui/PasswordEdit.h
@@ -41,7 +41,7 @@ signals:
 
 private slots:
     void updateStylesheet();
-    void autocompletePassword(QString password);
+    void autocompletePassword(const QString& password);
 
 private:
     bool passwordsEqual() const;
diff --git a/src/gui/SearchWidget.h b/src/gui/SearchWidget.h
index 1d95c664b..0ec3287c1 100644
--- a/src/gui/SearchWidget.h
+++ b/src/gui/SearchWidget.h
@@ -35,7 +35,7 @@ class SearchWidget : public QWidget
     Q_OBJECT
 
 public:
-    explicit SearchWidget(QWidget* parent = 0);
+    explicit SearchWidget(QWidget* parent = nullptr);
     ~SearchWidget();
 
     void connectSignals(SignalMultiplexer& mx);
@@ -55,7 +55,7 @@ signals:
     void enterPressed();
 
 public slots:
-    void databaseChanged(DatabaseWidget* dbWidget = 0);
+    void databaseChanged(DatabaseWidget* dbWidget = nullptr);
 
 private slots:
     void startSearchTimer();
diff --git a/src/gui/csvImport/CsvImportWidget.cpp b/src/gui/csvImport/CsvImportWidget.cpp
index 4cb219a77..3b623f73d 100644
--- a/src/gui/csvImport/CsvImportWidget.cpp
+++ b/src/gui/csvImport/CsvImportWidget.cpp
@@ -315,7 +315,7 @@ void CsvImportWidget::setRootGroup()
         m_db->rootGroup()->setName("Root");
 }
 
-Group* CsvImportWidget::splitGroups(QString label)
+Group* CsvImportWidget::splitGroups(const QString& label)
 {
     // extract group names from nested path provided in "label"
     Group* current = m_db->rootGroup();
@@ -345,7 +345,7 @@ Group* CsvImportWidget::splitGroups(QString label)
     return current;
 }
 
-Group* CsvImportWidget::hasChildren(Group* current, QString groupName)
+Group* CsvImportWidget::hasChildren(Group* current, const QString& groupName)
 {
     // returns the group whose name is "groupName" and is child of "current" group
     for (Group* group : current->children()) {
diff --git a/src/gui/csvImport/CsvImportWidget.h b/src/gui/csvImport/CsvImportWidget.h
index cd13836f0..a5807eefd 100644
--- a/src/gui/csvImport/CsvImportWidget.h
+++ b/src/gui/csvImport/CsvImportWidget.h
@@ -68,8 +68,8 @@ private:
     QStringList m_fieldSeparatorList;
     void configParser();
     void updateTableview();
-    Group* splitGroups(QString label);
-    Group* hasChildren(Group* current, QString groupName);
+    Group* splitGroups(const QString& label);
+    Group* hasChildren(Group* current, const QString& groupName);
     QString formatStatusText() const;
 };
 
diff --git a/src/gui/csvImport/CsvParserModel.cpp b/src/gui/csvImport/CsvParserModel.cpp
index e69ea1853..269fbdd62 100644
--- a/src/gui/csvImport/CsvParserModel.cpp
+++ b/src/gui/csvImport/CsvParserModel.cpp
@@ -18,6 +18,8 @@
 
 #include "CsvParserModel.h"
 
+#include <utility>
+
 CsvParserModel::CsvParserModel(QObject* parent)
     : QAbstractTableModel(parent)
     , m_skipped(0)
@@ -36,9 +38,9 @@ void CsvParserModel::setFilename(const QString& filename)
 QString CsvParserModel::getFileInfo()
 {
     QString a(tr("%1, %2, %3", "file info: bytes, rows, columns")
-                  .arg(tr("%n byte(s)", nullptr, getFileSize()))
-                  .arg(tr("%n row(s)", nullptr, getCsvRows()))
-                  .arg(tr("%n column(s)", nullptr, qMax(0, getCsvCols() - 1))));
+                  .arg(tr("%n byte(s)", nullptr, getFileSize()),
+                       tr("%n row(s)", nullptr, getCsvRows()),
+                       tr("%n column(s)", nullptr, qMax(0, getCsvCols() - 1))));
     return a;
 }
 
@@ -92,7 +94,7 @@ void CsvParserModel::setSkippedRows(int skipped)
 
 void CsvParserModel::setHeaderLabels(QStringList l)
 {
-    m_columnHeader = l;
+    m_columnHeader = std::move(l);
 }
 
 int CsvParserModel::rowCount(const QModelIndex& parent) const
diff --git a/src/gui/dbsettings/DatabaseSettingsWidgetBrowser.cpp b/src/gui/dbsettings/DatabaseSettingsWidgetBrowser.cpp
index 0dae1486d..a91744cdb 100644
--- a/src/gui/dbsettings/DatabaseSettingsWidgetBrowser.cpp
+++ b/src/gui/dbsettings/DatabaseSettingsWidgetBrowser.cpp
@@ -38,7 +38,7 @@ DatabaseSettingsWidgetBrowser::DatabaseSettingsWidgetBrowser(QWidget* parent)
     m_ui->customDataTable->setModel(m_customDataModel);
 
     settingsWarning();
-    connect(m_ui->customDataTable->selectionModel(), SIGNAL(selectionChanged(QItemSelection, QItemSelection)),
+    connect(m_ui->customDataTable->selectionModel(), SIGNAL(selectionChanged(QItemSelection,QItemSelection)),
             SLOT(toggleRemoveButton(QItemSelection)));
     connect(m_ui->removeCustomDataButton, SIGNAL(clicked()), SLOT(removeSelectedKey()));
     connect(m_ui->convertToCustomData, SIGNAL(clicked()), this, SLOT(convertAttributesToCustomData()));
diff --git a/src/gui/entry/AutoTypeMatchModel.cpp b/src/gui/entry/AutoTypeMatchModel.cpp
index 1a6a6ba3b..197b3cd96 100644
--- a/src/gui/entry/AutoTypeMatchModel.cpp
+++ b/src/gui/entry/AutoTypeMatchModel.cpp
@@ -37,7 +37,7 @@ AutoTypeMatch AutoTypeMatchModel::matchFromIndex(const QModelIndex& index) const
     return m_matches.at(index.row());
 }
 
-QModelIndex AutoTypeMatchModel::indexFromMatch(AutoTypeMatch match) const
+QModelIndex AutoTypeMatchModel::indexFromMatch(const AutoTypeMatch& match) const
 {
     int row = m_matches.indexOf(match);
     Q_ASSERT(row != -1);
diff --git a/src/gui/entry/AutoTypeMatchModel.h b/src/gui/entry/AutoTypeMatchModel.h
index 791dbc3df..58b89465b 100644
--- a/src/gui/entry/AutoTypeMatchModel.h
+++ b/src/gui/entry/AutoTypeMatchModel.h
@@ -41,7 +41,7 @@ public:
 
     explicit AutoTypeMatchModel(QObject* parent = nullptr);
     AutoTypeMatch matchFromIndex(const QModelIndex& index) const;
-    QModelIndex indexFromMatch(AutoTypeMatch match) const;
+    QModelIndex indexFromMatch(const AutoTypeMatch& match) const;
 
     int rowCount(const QModelIndex& parent = QModelIndex()) const override;
     int columnCount(const QModelIndex& parent = QModelIndex()) const override;
diff --git a/src/gui/entry/AutoTypeMatchView.cpp b/src/gui/entry/AutoTypeMatchView.cpp
index 2750082d8..087f2cc64 100644
--- a/src/gui/entry/AutoTypeMatchView.cpp
+++ b/src/gui/entry/AutoTypeMatchView.cpp
@@ -44,7 +44,7 @@ AutoTypeMatchView::AutoTypeMatchView(QWidget* parent)
 
     connect(this, SIGNAL(doubleClicked(QModelIndex)), SLOT(emitMatchActivated(QModelIndex)));
     connect(
-        selectionModel(), SIGNAL(selectionChanged(QItemSelection, QItemSelection)), SIGNAL(matchSelectionChanged()));
+        selectionModel(), SIGNAL(selectionChanged(QItemSelection,QItemSelection)), SIGNAL(matchSelectionChanged()));
 }
 
 void AutoTypeMatchView::keyPressEvent(QKeyEvent* event)
@@ -98,7 +98,7 @@ AutoTypeMatch AutoTypeMatchView::currentMatch()
     return AutoTypeMatch();
 }
 
-void AutoTypeMatchView::setCurrentMatch(AutoTypeMatch match)
+void AutoTypeMatchView::setCurrentMatch(const AutoTypeMatch& match)
 {
     selectionModel()->setCurrentIndex(m_sortModel->mapFromSource(m_model->indexFromMatch(match)),
                                       QItemSelectionModel::ClearAndSelect | QItemSelectionModel::Rows);
diff --git a/src/gui/entry/AutoTypeMatchView.h b/src/gui/entry/AutoTypeMatchView.h
index 14ad9ea2a..b9f3f3aa5 100644
--- a/src/gui/entry/AutoTypeMatchView.h
+++ b/src/gui/entry/AutoTypeMatchView.h
@@ -34,7 +34,7 @@ class AutoTypeMatchView : public QTreeView
 public:
     explicit AutoTypeMatchView(QWidget* parent = nullptr);
     AutoTypeMatch currentMatch();
-    void setCurrentMatch(AutoTypeMatch match);
+    void setCurrentMatch(const AutoTypeMatch& match);
     AutoTypeMatch matchFromIndex(const QModelIndex& index);
     void setMatchList(const QList<AutoTypeMatch>& matches);
     void setFirstMatchActive();
diff --git a/src/gui/entry/EditEntryWidget.cpp b/src/gui/entry/EditEntryWidget.cpp
index e8a450026..8a54b23e3 100644
--- a/src/gui/entry/EditEntryWidget.cpp
+++ b/src/gui/entry/EditEntryWidget.cpp
@@ -103,8 +103,8 @@ EditEntryWidget::EditEntryWidget(QWidget* parent)
     connect(this, SIGNAL(rejected()), SLOT(cancel()));
     connect(this, SIGNAL(apply()), SLOT(commitEntry()));
     connect(m_iconsWidget,
-            SIGNAL(messageEditEntry(QString, MessageWidget::MessageType)),
-            SLOT(showMessage(QString, MessageWidget::MessageType)));
+            SIGNAL(messageEditEntry(QString,MessageWidget::MessageType)),
+            SLOT(showMessage(QString,MessageWidget::MessageType)));
     connect(m_iconsWidget, SIGNAL(messageEditEntryDismiss()), SLOT(hideMessage()));
 
     m_mainUi->passwordGenerator->layout()->setContentsMargins(0, 0, 0, 0);
@@ -161,7 +161,7 @@ void EditEntryWidget::setupAdvanced()
     connect(m_advancedUi->protectAttributeButton, SIGNAL(toggled(bool)), SLOT(protectCurrentAttribute(bool)));
     connect(m_advancedUi->revealAttributeButton, SIGNAL(clicked(bool)), SLOT(revealCurrentAttribute()));
     connect(m_advancedUi->attributesView->selectionModel(),
-            SIGNAL(currentChanged(QModelIndex, QModelIndex)),
+            SIGNAL(currentChanged(QModelIndex,QModelIndex)),
             SLOT(updateCurrentAttribute()));
     connect(m_advancedUi->fgColorButton, SIGNAL(clicked()), SLOT(pickColor()));
     connect(m_advancedUi->bgColorButton, SIGNAL(clicked()), SLOT(pickColor()));
@@ -192,11 +192,11 @@ void EditEntryWidget::setupAutoType()
     connect(m_autoTypeUi->assocAddButton, SIGNAL(clicked()), SLOT(insertAutoTypeAssoc()));
     connect(m_autoTypeUi->assocRemoveButton, SIGNAL(clicked()), SLOT(removeAutoTypeAssoc()));
     connect(m_autoTypeUi->assocView->selectionModel(),
-            SIGNAL(currentRowChanged(QModelIndex, QModelIndex)),
+            SIGNAL(currentRowChanged(QModelIndex,QModelIndex)),
             SLOT(updateAutoTypeEnabled()));
     connect(m_autoTypeAssocModel, SIGNAL(modelReset()), SLOT(updateAutoTypeEnabled()));
     connect(m_autoTypeUi->assocView->selectionModel(),
-            SIGNAL(currentRowChanged(QModelIndex, QModelIndex)),
+            SIGNAL(currentRowChanged(QModelIndex,QModelIndex)),
             SLOT(loadCurrentAssoc(QModelIndex)));
     connect(m_autoTypeAssocModel, SIGNAL(modelReset()), SLOT(clearCurrentAssoc()));
     connect(m_autoTypeUi->windowTitleCombo, SIGNAL(editTextChanged(QString)), SLOT(applyCurrentAssoc()));
@@ -225,8 +225,8 @@ void EditEntryWidget::setupHistory()
 
     connect(m_historyUi->historyView, SIGNAL(activated(QModelIndex)), SLOT(histEntryActivated(QModelIndex)));
     connect(m_historyUi->historyView->selectionModel(),
-            SIGNAL(currentChanged(QModelIndex, QModelIndex)),
-            SLOT(updateHistoryButtons(QModelIndex, QModelIndex)));
+            SIGNAL(currentChanged(QModelIndex,QModelIndex)),
+            SLOT(updateHistoryButtons(QModelIndex,QModelIndex)));
     connect(m_historyUi->showButton, SIGNAL(clicked()), SLOT(showHistoryEntry()));
     connect(m_historyUi->restoreButton, SIGNAL(clicked()), SLOT(restoreHistoryEntry()));
     connect(m_historyUi->deleteButton, SIGNAL(clicked()), SLOT(deleteHistoryEntry()));
@@ -236,14 +236,14 @@ void EditEntryWidget::setupHistory()
 void EditEntryWidget::setupEntryUpdate()
 {
     // Entry tab
-    connect(m_mainUi->titleEdit, SIGNAL(textChanged(const QString&)), this, SLOT(setUnsavedChanges()));
-    connect(m_mainUi->usernameEdit, SIGNAL(textChanged(const QString&)), this, SLOT(setUnsavedChanges()));
-    connect(m_mainUi->passwordEdit, SIGNAL(textChanged(const QString&)), this, SLOT(setUnsavedChanges()));
-    connect(m_mainUi->passwordRepeatEdit, SIGNAL(textChanged(const QString&)), this, SLOT(setUnsavedChanges()));
-    connect(m_mainUi->urlEdit, SIGNAL(textChanged(const QString&)), this, SLOT(setUnsavedChanges()));
+    connect(m_mainUi->titleEdit, SIGNAL(textChanged(QString)), this, SLOT(setUnsavedChanges()));
+    connect(m_mainUi->usernameEdit, SIGNAL(textChanged(QString)), this, SLOT(setUnsavedChanges()));
+    connect(m_mainUi->passwordEdit, SIGNAL(textChanged(QString)), this, SLOT(setUnsavedChanges()));
+    connect(m_mainUi->passwordRepeatEdit, SIGNAL(textChanged(QString)), this, SLOT(setUnsavedChanges()));
+    connect(m_mainUi->urlEdit, SIGNAL(textChanged(QString)), this, SLOT(setUnsavedChanges()));
     connect(m_mainUi->expireCheck, SIGNAL(stateChanged(int)), this, SLOT(setUnsavedChanges()));
     connect(m_mainUi->notesEnabled, SIGNAL(stateChanged(int)), this, SLOT(setUnsavedChanges()));
-    connect(m_mainUi->expireDatePicker, SIGNAL(dateTimeChanged(const QDateTime&)), this, SLOT(setUnsavedChanges()));
+    connect(m_mainUi->expireDatePicker, SIGNAL(dateTimeChanged(QDateTime)), this, SLOT(setUnsavedChanges()));
     connect(m_mainUi->notesEdit, SIGNAL(textChanged()), this, SLOT(setUnsavedChanges()));
 
     // Advanced tab
@@ -261,10 +261,10 @@ void EditEntryWidget::setupEntryUpdate()
     connect(m_autoTypeUi->customWindowSequenceButton, SIGNAL(stateChanged(int)), this, SLOT(setUnsavedChanges()));
     connect(m_autoTypeUi->inheritSequenceButton, SIGNAL(toggled(bool)), this, SLOT(setUnsavedChanges()));
     connect(m_autoTypeUi->customSequenceButton, SIGNAL(toggled(bool)), this, SLOT(setUnsavedChanges()));
-    connect(m_autoTypeUi->windowSequenceEdit, SIGNAL(textChanged(const QString&)), this, SLOT(setUnsavedChanges()));
-    connect(m_autoTypeUi->sequenceEdit, SIGNAL(textChanged(const QString&)), this, SLOT(setUnsavedChanges()));
+    connect(m_autoTypeUi->windowSequenceEdit, SIGNAL(textChanged(QString)), this, SLOT(setUnsavedChanges()));
+    connect(m_autoTypeUi->sequenceEdit, SIGNAL(textChanged(QString)), this, SLOT(setUnsavedChanges()));
     connect(m_autoTypeUi->windowTitleCombo, SIGNAL(currentIndexChanged(int)), this, SLOT(setUnsavedChanges()));
-    connect(m_autoTypeUi->windowTitleCombo, SIGNAL(editTextChanged(const QString&)), this, SLOT(setUnsavedChanges()));
+    connect(m_autoTypeUi->windowTitleCombo, SIGNAL(editTextChanged(QString)), this, SLOT(setUnsavedChanges()));
 
 // Properties and History tabs don't need extra connections
 
@@ -275,8 +275,8 @@ void EditEntryWidget::setupEntryUpdate()
         connect(m_sshAgentUi->externalFileRadioButton, SIGNAL(toggled(bool)), this, SLOT(setUnsavedChanges()));
         connect(m_sshAgentUi->attachmentComboBox, SIGNAL(currentIndexChanged(int)), this, SLOT(setUnsavedChanges()));
         connect(
-            m_sshAgentUi->attachmentComboBox, SIGNAL(editTextChanged(const QString&)), this, SLOT(setUnsavedChanges()));
-        connect(m_sshAgentUi->externalFileEdit, SIGNAL(textChanged(const QString&)), this, SLOT(setUnsavedChanges()));
+            m_sshAgentUi->attachmentComboBox, SIGNAL(editTextChanged(QString)), this, SLOT(setUnsavedChanges()));
+        connect(m_sshAgentUi->externalFileEdit, SIGNAL(textChanged(QString)), this, SLOT(setUnsavedChanges()));
         connect(m_sshAgentUi->addKeyToAgentCheckBox, SIGNAL(stateChanged(int)), this, SLOT(setUnsavedChanges()));
         connect(m_sshAgentUi->removeKeyFromAgentCheckBox, SIGNAL(stateChanged(int)), this, SLOT(setUnsavedChanges()));
         connect(
@@ -1269,13 +1269,13 @@ QMenu* EditEntryWidget::createPresetsMenu()
     QMenu* expirePresetsMenu = new QMenu(this);
     expirePresetsMenu->addAction(tr("Tomorrow"))->setData(QVariant::fromValue(TimeDelta::fromDays(1)));
     expirePresetsMenu->addSeparator();
-    expirePresetsMenu->addAction(tr("%n week(s)", 0, 1))->setData(QVariant::fromValue(TimeDelta::fromDays(7)));
-    expirePresetsMenu->addAction(tr("%n week(s)", 0, 2))->setData(QVariant::fromValue(TimeDelta::fromDays(14)));
-    expirePresetsMenu->addAction(tr("%n week(s)", 0, 3))->setData(QVariant::fromValue(TimeDelta::fromDays(21)));
+    expirePresetsMenu->addAction(tr("%n week(s)", nullptr, 1))->setData(QVariant::fromValue(TimeDelta::fromDays(7)));
+    expirePresetsMenu->addAction(tr("%n week(s)", nullptr, 2))->setData(QVariant::fromValue(TimeDelta::fromDays(14)));
+    expirePresetsMenu->addAction(tr("%n week(s)", nullptr, 3))->setData(QVariant::fromValue(TimeDelta::fromDays(21)));
     expirePresetsMenu->addSeparator();
-    expirePresetsMenu->addAction(tr("%n month(s)", 0, 1))->setData(QVariant::fromValue(TimeDelta::fromMonths(1)));
-    expirePresetsMenu->addAction(tr("%n month(s)", 0, 3))->setData(QVariant::fromValue(TimeDelta::fromMonths(3)));
-    expirePresetsMenu->addAction(tr("%n month(s)", 0, 6))->setData(QVariant::fromValue(TimeDelta::fromMonths(6)));
+    expirePresetsMenu->addAction(tr("%n month(s)", nullptr, 1))->setData(QVariant::fromValue(TimeDelta::fromMonths(1)));
+    expirePresetsMenu->addAction(tr("%n month(s)", nullptr, 3))->setData(QVariant::fromValue(TimeDelta::fromMonths(3)));
+    expirePresetsMenu->addAction(tr("%n month(s)", nullptr, 6))->setData(QVariant::fromValue(TimeDelta::fromMonths(6)));
     expirePresetsMenu->addSeparator();
     expirePresetsMenu->addAction(tr("%n year(s)", 0, 1))->setData(QVariant::fromValue(TimeDelta::fromYears(1)));
     expirePresetsMenu->addAction(tr("%n year(s)", 0, 2))->setData(QVariant::fromValue(TimeDelta::fromYears(2)));
@@ -1311,8 +1311,7 @@ void EditEntryWidget::pickColor()
         oldColor = QColor(m_advancedUi->bgColorButton->property("color").toString());
     }
 
-    QColorDialog colorDialog(this);
-    QColor newColor = colorDialog.getColor(oldColor);
+    QColor newColor = QColorDialog::getColor(oldColor);
     if (newColor.isValid()) {
         setupColorButton(isForeground, newColor);
         setUnsavedChanges(true);
diff --git a/src/gui/entry/EditEntryWidget_p.h b/src/gui/entry/EditEntryWidget_p.h
index 0ba01cd51..dd0bac8b8 100644
--- a/src/gui/entry/EditEntryWidget_p.h
+++ b/src/gui/entry/EditEntryWidget_p.h
@@ -24,7 +24,7 @@
 class AttributesListView : public QListView
 {
 public:
-    explicit AttributesListView(QWidget* parent = 0)
+    explicit AttributesListView(QWidget* parent = nullptr)
         : QListView(parent)
     {
         setSizePolicy(QSizePolicy::Preferred, QSizePolicy::Expanding);
diff --git a/src/gui/entry/EntryAttachmentsWidget.cpp b/src/gui/entry/EntryAttachmentsWidget.cpp
index c1897d898..6f42a1994 100644
--- a/src/gui/entry/EntryAttachmentsWidget.cpp
+++ b/src/gui/entry/EntryAttachmentsWidget.cpp
@@ -44,7 +44,7 @@ EntryAttachmentsWidget::EntryAttachmentsWidget(QWidget* parent)
     connect(this, SIGNAL(readOnlyChanged(bool)), SLOT(updateButtonsEnabled()));
     connect(m_attachmentsModel, SIGNAL(modelReset()), SLOT(updateButtonsEnabled()));
     connect(m_ui->attachmentsView->selectionModel(),
-            SIGNAL(selectionChanged(QItemSelection, QItemSelection)),
+            SIGNAL(selectionChanged(QItemSelection,QItemSelection)),
             SLOT(updateButtonsEnabled()));
 
     connect(m_ui->attachmentsView, SIGNAL(doubleClicked(QModelIndex)), SLOT(openAttachment(QModelIndex)));
diff --git a/src/gui/entry/EntryAttributesModel.cpp b/src/gui/entry/EntryAttributesModel.cpp
index ddb31d624..373fcc6c7 100644
--- a/src/gui/entry/EntryAttributesModel.cpp
+++ b/src/gui/entry/EntryAttributesModel.cpp
@@ -47,8 +47,8 @@ void EntryAttributesModel::setEntryAttributes(EntryAttributes* entryAttributes)
         connect(m_entryAttributes, SIGNAL(aboutToBeRemoved(QString)), SLOT(attributeAboutToRemove(QString)));
         connect(m_entryAttributes, SIGNAL(removed(QString)), SLOT(attributeRemove()));
         connect(
-            m_entryAttributes, SIGNAL(aboutToRename(QString, QString)), SLOT(attributeAboutToRename(QString, QString)));
-        connect(m_entryAttributes, SIGNAL(renamed(QString, QString)), SLOT(attributeRename(QString, QString)));
+            m_entryAttributes, SIGNAL(aboutToRename(QString,QString)), SLOT(attributeAboutToRename(QString,QString)));
+        connect(m_entryAttributes, SIGNAL(renamed(QString,QString)), SLOT(attributeRename(QString,QString)));
         connect(m_entryAttributes, SIGNAL(aboutToBeReset()), SLOT(aboutToReset()));
         connect(m_entryAttributes, SIGNAL(reset()), SLOT(reset()));
     }
diff --git a/src/gui/entry/EntryHistoryModel.cpp b/src/gui/entry/EntryHistoryModel.cpp
index aaec3de62..2506e06d7 100644
--- a/src/gui/entry/EntryHistoryModel.cpp
+++ b/src/gui/entry/EntryHistoryModel.cpp
@@ -54,7 +54,7 @@ QVariant EntryHistoryModel::data(const QModelIndex& index, int role) const
 
     if (role == Qt::DisplayRole || role == Qt::UserRole) {
         Entry* entry = entryFromIndex(index);
-        TimeInfo timeInfo = entry->timeInfo();
+        const TimeInfo& timeInfo = entry->timeInfo();
         QDateTime lastModificationLocalTime = timeInfo.lastModificationTime().toLocalTime();
         switch (index.column()) {
         case 0:
diff --git a/src/gui/entry/EntryModel.cpp b/src/gui/entry/EntryModel.cpp
index 0616374ac..8cbf4bfe4 100644
--- a/src/gui/entry/EntryModel.cpp
+++ b/src/gui/entry/EntryModel.cpp
@@ -208,12 +208,12 @@ QVariant EntryModel::data(const QModelIndex& index, int role) const
         case Attachments: {
             // Display comma-separated list of attachments
             QList<QString> attachments = entry->attachments()->keys();
-            for (int i = 0; i < attachments.size(); ++i) {
+            for (const auto& attachment : attachments) {
                 if (result.isEmpty()) {
-                    result.append(attachments.at(i));
+                    result.append(attachment);
                     continue;
                 }
-                result.append(QString(", ") + attachments.at(i));
+                result.append(QString(", ") + attachment);
             }
             return result;
         }
@@ -331,7 +331,7 @@ QVariant EntryModel::headerData(int section, Qt::Orientation orientation, int ro
 
 Qt::DropActions EntryModel::supportedDropActions() const
 {
-    return 0;
+    return Qt::IgnoreAction;
 }
 
 Qt::DropActions EntryModel::supportedDragActions() const
diff --git a/src/gui/entry/EntryView.cpp b/src/gui/entry/EntryView.cpp
index 05c55ad82..d63260c39 100644
--- a/src/gui/entry/EntryView.cpp
+++ b/src/gui/entry/EntryView.cpp
@@ -51,7 +51,7 @@ EntryView::EntryView(QWidget* parent)
 
     connect(this, SIGNAL(doubleClicked(QModelIndex)), SLOT(emitEntryActivated(QModelIndex)));
     connect(
-        selectionModel(), SIGNAL(selectionChanged(QItemSelection, QItemSelection)), SIGNAL(entrySelectionChanged()));
+        selectionModel(), SIGNAL(selectionChanged(QItemSelection,QItemSelection)), SIGNAL(entrySelectionChanged()));
     connect(m_model, SIGNAL(switchedToListMode()), SLOT(switchToListMode()));
     connect(m_model, SIGNAL(switchedToSearchMode()), SLOT(switchToSearchMode()));
     connect(m_model, SIGNAL(usernamesHiddenChanged()), SIGNAL(viewStateChanged()));
@@ -97,10 +97,10 @@ EntryView::EntryView(QWidget* parent)
     header()->setContextMenuPolicy(Qt::CustomContextMenu);
 
     connect(header(), SIGNAL(customContextMenuRequested(QPoint)), SLOT(showHeaderMenu(QPoint)));
-    connect(header(), SIGNAL(sectionCountChanged(int, int)), SIGNAL(viewStateChanged()));
-    connect(header(), SIGNAL(sectionMoved(int, int, int)), SIGNAL(viewStateChanged()));
-    connect(header(), SIGNAL(sectionResized(int, int, int)), SIGNAL(viewStateChanged()));
-    connect(header(), SIGNAL(sortIndicatorChanged(int, Qt::SortOrder)), SIGNAL(viewStateChanged()));
+    connect(header(), SIGNAL(sectionCountChanged(int,int)), SIGNAL(viewStateChanged()));
+    connect(header(), SIGNAL(sectionMoved(int,int,int)), SIGNAL(viewStateChanged()));
+    connect(header(), SIGNAL(sectionResized(int,int,int)), SIGNAL(viewStateChanged()));
+    connect(header(), SIGNAL(sortIndicatorChanged(int,Qt::SortOrder)), SIGNAL(viewStateChanged()));
 
     resetFixedColumns();
 
diff --git a/src/gui/group/EditGroupWidget.cpp b/src/gui/group/EditGroupWidget.cpp
index 2abfa5544..44276a9f3 100644
--- a/src/gui/group/EditGroupWidget.cpp
+++ b/src/gui/group/EditGroupWidget.cpp
@@ -49,8 +49,8 @@ EditGroupWidget::EditGroupWidget(QWidget* parent)
     connect(this, SIGNAL(rejected()), SLOT(cancel()));
 
     connect(m_editGroupWidgetIcons,
-            SIGNAL(messageEditEntry(QString, MessageWidget::MessageType)),
-            SLOT(showMessage(QString, MessageWidget::MessageType)));
+            SIGNAL(messageEditEntry(QString,MessageWidget::MessageType)),
+            SLOT(showMessage(QString,MessageWidget::MessageType)));
     connect(m_editGroupWidgetIcons, SIGNAL(messageEditEntryDismiss()), SLOT(hideMessage()));
 }
 
diff --git a/src/gui/group/GroupModel.cpp b/src/gui/group/GroupModel.cpp
index a3c72b792..791f6ce33 100644
--- a/src/gui/group/GroupModel.cpp
+++ b/src/gui/group/GroupModel.cpp
@@ -44,11 +44,11 @@ void GroupModel::changeDatabase(Database* newDb)
     m_db = newDb;
 
     connect(m_db, SIGNAL(groupDataChanged(Group*)), SLOT(groupDataChanged(Group*)));
-    connect(m_db, SIGNAL(groupAboutToAdd(Group*, int)), SLOT(groupAboutToAdd(Group*, int)));
+    connect(m_db, SIGNAL(groupAboutToAdd(Group*,int)), SLOT(groupAboutToAdd(Group*,int)));
     connect(m_db, SIGNAL(groupAdded()), SLOT(groupAdded()));
     connect(m_db, SIGNAL(groupAboutToRemove(Group*)), SLOT(groupAboutToRemove(Group*)));
     connect(m_db, SIGNAL(groupRemoved()), SLOT(groupRemoved()));
-    connect(m_db, SIGNAL(groupAboutToMove(Group*, Group*, int)), SLOT(groupAboutToMove(Group*, Group*, int)));
+    connect(m_db, SIGNAL(groupAboutToMove(Group*,Group*,int)), SLOT(groupAboutToMove(Group*,Group*,int)));
     connect(m_db, SIGNAL(groupMoved()), SLOT(groupMoved()));
 
     endResetModel();
diff --git a/src/gui/group/GroupView.cpp b/src/gui/group/GroupView.cpp
index fd6748006..ee3913948 100644
--- a/src/gui/group/GroupView.cpp
+++ b/src/gui/group/GroupView.cpp
@@ -36,10 +36,10 @@ GroupView::GroupView(Database* db, QWidget* parent)
 
     connect(this, SIGNAL(expanded(QModelIndex)), this, SLOT(expandedChanged(QModelIndex)));
     connect(this, SIGNAL(collapsed(QModelIndex)), this, SLOT(expandedChanged(QModelIndex)));
-    connect(m_model, SIGNAL(rowsInserted(QModelIndex, int, int)), SLOT(syncExpandedState(QModelIndex, int, int)));
+    connect(m_model, SIGNAL(rowsInserted(QModelIndex,int,int)), SLOT(syncExpandedState(QModelIndex,int,int)));
     connect(m_model, SIGNAL(modelReset()), SLOT(modelReset()));
 
-    connect(selectionModel(), SIGNAL(currentChanged(QModelIndex, QModelIndex)), SLOT(emitGroupChanged()));
+    connect(selectionModel(), SIGNAL(currentChanged(QModelIndex,QModelIndex)), SLOT(emitGroupChanged()));
 
     connect(this, SIGNAL(clicked(QModelIndex)), SLOT(emitGroupPressed(QModelIndex)));
 
diff --git a/src/gui/masterkey/KeyComponentWidget.cpp b/src/gui/masterkey/KeyComponentWidget.cpp
index 45f133b44..72367ecbe 100644
--- a/src/gui/masterkey/KeyComponentWidget.cpp
+++ b/src/gui/masterkey/KeyComponentWidget.cpp
@@ -38,8 +38,8 @@ KeyComponentWidget::KeyComponentWidget(const QString& name, QWidget* parent)
 
     connect(m_ui->stackedWidget, SIGNAL(currentChanged(int)), SLOT(reset()));
 
-    connect(this, SIGNAL(nameChanged(const QString&)), SLOT(updateComponentName(const QString&)));
-    connect(this, SIGNAL(descriptionChanged(const QString&)), SLOT(updateComponentDescription(const QString&)));
+    connect(this, SIGNAL(nameChanged(QString)), SLOT(updateComponentName(QString)));
+    connect(this, SIGNAL(descriptionChanged(QString)), SLOT(updateComponentDescription(QString)));
     connect(this, SIGNAL(componentAddRequested()), SLOT(doAdd()));
     connect(this, SIGNAL(componentEditRequested()), SLOT(doEdit()));
     connect(this, SIGNAL(componentRemovalRequested()), SLOT(doRemove()));
diff --git a/src/gui/masterkey/PasswordEditWidget.cpp b/src/gui/masterkey/PasswordEditWidget.cpp
index dc43f9159..4006a0b1e 100644
--- a/src/gui/masterkey/PasswordEditWidget.cpp
+++ b/src/gui/masterkey/PasswordEditWidget.cpp
@@ -107,7 +107,7 @@ void PasswordEditWidget::showPasswordGenerator()
     layout->addWidget(pwGenerator);
 
     pwGenerator->setStandaloneMode(false);
-    connect(pwGenerator, SIGNAL(appliedPassword(const QString&)), SLOT(setPassword(const QString&)));
+    connect(pwGenerator, SIGNAL(appliedPassword(QString)), SLOT(setPassword(QString)));
     connect(pwGenerator, SIGNAL(dialogTerminated()), &pwDialog, SLOT(close()));
 
     pwGenerator->setPasswordVisible(isPasswordVisible());
diff --git a/src/gui/masterkey/YubiKeyEditWidget.cpp b/src/gui/masterkey/YubiKeyEditWidget.cpp
index bae3a3d1e..27e0a4cf0 100644
--- a/src/gui/masterkey/YubiKeyEditWidget.cpp
+++ b/src/gui/masterkey/YubiKeyEditWidget.cpp
@@ -75,7 +75,7 @@ QWidget* YubiKeyEditWidget::componentEditWidget()
 #ifdef WITH_XC_YUBIKEY
     connect(m_compUi->buttonRedetectYubikey, SIGNAL(clicked()), SLOT(pollYubikey()));
 
-    connect(YubiKey::instance(), SIGNAL(detected(int, bool)), SLOT(yubikeyDetected(int, bool)), Qt::QueuedConnection);
+    connect(YubiKey::instance(), SIGNAL(detected(int,bool)), SLOT(yubikeyDetected(int,bool)), Qt::QueuedConnection);
     connect(YubiKey::instance(), SIGNAL(notFound()), SLOT(noYubikeyFound()), Qt::QueuedConnection);
 
     pollYubikey();
diff --git a/src/keys/CompositeKey.cpp b/src/keys/CompositeKey.cpp
index 4fca7d320..10e86318b 100644
--- a/src/keys/CompositeKey.cpp
+++ b/src/keys/CompositeKey.cpp
@@ -153,7 +153,7 @@ bool CompositeKey::challenge(const QByteArray& seed, QByteArray& result) const
  *
  * @param key the key
  */
-void CompositeKey::addKey(QSharedPointer<Key> key)
+void CompositeKey::addKey(const QSharedPointer<Key>& key)
 {
     m_keys.append(key);
 }
@@ -173,7 +173,7 @@ const QList<QSharedPointer<Key>>& CompositeKey::keys() const
  *
  * @param key the key
  */
-void CompositeKey::addChallengeResponseKey(QSharedPointer<ChallengeResponseKey> key)
+void CompositeKey::addChallengeResponseKey(const QSharedPointer<ChallengeResponseKey>& key)
 {
     m_challengeResponseKeys.append(key);
 }
diff --git a/src/keys/CompositeKey.h b/src/keys/CompositeKey.h
index 43c624acb..f32f3a1a1 100644
--- a/src/keys/CompositeKey.h
+++ b/src/keys/CompositeKey.h
@@ -42,10 +42,10 @@ public:
     Q_REQUIRED_RESULT bool transform(const Kdf& kdf, QByteArray& result) const;
     bool challenge(const QByteArray& seed, QByteArray& result) const;
 
-    void addKey(QSharedPointer<Key> key);
+    void addKey(const QSharedPointer<Key>& key);
     const QList<QSharedPointer<Key>>& keys() const;
 
-    void addChallengeResponseKey(QSharedPointer<ChallengeResponseKey> key);\
+    void addChallengeResponseKey(const QSharedPointer<ChallengeResponseKey>& key);\
     const QList<QSharedPointer<ChallengeResponseKey>>& challengeResponseKeys() const;
 
 private:
diff --git a/src/keys/drivers/YubiKey.cpp b/src/keys/drivers/YubiKey.cpp
index b94916197..b6905fc38 100644
--- a/src/keys/drivers/YubiKey.cpp
+++ b/src/keys/drivers/YubiKey.cpp
@@ -37,8 +37,8 @@
 #define m_ykds (static_cast<YK_STATUS*>(m_ykds_void))
 
 YubiKey::YubiKey()
-    : m_yk_void(NULL)
-    , m_ykds_void(NULL)
+    : m_yk_void(nullptr)
+    , m_ykds_void(nullptr)
     , m_mutex(QMutex::Recursive)
 {
 }
@@ -59,7 +59,7 @@ bool YubiKey::init()
     m_mutex.lock();
 
     // previously initialized
-    if (m_yk != NULL && m_ykds != NULL) {
+    if (m_yk != nullptr && m_ykds != nullptr) {
 
         if (yk_get_status(m_yk, m_ykds)) {
             // Still connected
@@ -78,15 +78,15 @@ bool YubiKey::init()
 
     // TODO: handle multiple attached hardware devices
     m_yk_void = static_cast<void*>(yk_open_first_key());
-    if (m_yk == NULL) {
+    if (m_yk == nullptr) {
         m_mutex.unlock();
         return false;
     }
 
     m_ykds_void = static_cast<void*>(ykds_alloc());
-    if (m_ykds == NULL) {
+    if (m_ykds == nullptr) {
         yk_close_key(m_yk);
-        m_yk_void = NULL;
+        m_yk_void = nullptr;
         m_mutex.unlock();
         return false;
     }
@@ -101,12 +101,12 @@ bool YubiKey::deinit()
 
     if (m_yk) {
         yk_close_key(m_yk);
-        m_yk_void = NULL;
+        m_yk_void = nullptr;
     }
 
     if (m_ykds) {
         ykds_free(m_ykds);
-        m_ykds_void = NULL;
+        m_ykds_void = nullptr;
     }
 
     m_mutex.unlock();
diff --git a/src/main.cpp b/src/main.cpp
index 0b5e0b1cb..9764c52d1 100644
--- a/src/main.cpp
+++ b/src/main.cpp
@@ -88,7 +88,7 @@ int main(int argc, char** argv)
     
     const QStringList fileNames = parser.positionalArguments();
 
-    if (app.isAlreadyRunning() && !parser.isSet(versionOption)) {
+    if (app.isAlreadyRunning()) {
         if (!fileNames.isEmpty()) {
             app.sendFileNamesToRunningInstance(fileNames);
         }
diff --git a/src/sshagent/BinaryStream.cpp b/src/sshagent/BinaryStream.cpp
index 2aa8ac1c7..2af04cee5 100644
--- a/src/sshagent/BinaryStream.cpp
+++ b/src/sshagent/BinaryStream.cpp
@@ -151,7 +151,7 @@ bool BinaryStream::readString(QString& str)
         return false;
     }
 
-    str = str.fromLatin1(ba);
+    str = QString::fromLatin1(ba);
     return true;
 }
 
diff --git a/src/sshagent/OpenSSHKey.cpp b/src/sshagent/OpenSSHKey.cpp
index 44684d620..9d1301a05 100644
--- a/src/sshagent/OpenSSHKey.cpp
+++ b/src/sshagent/OpenSSHKey.cpp
@@ -101,7 +101,7 @@ const QString OpenSSHKey::fingerprint(QCryptographicHash::Algorithm algo) const
 
     stream.writeString(m_type);
 
-    for (QByteArray ba : m_publicData) {
+    for (const QByteArray& ba : m_publicData) {
         stream.writeString(ba);
     }
 
@@ -137,7 +137,7 @@ const QString OpenSSHKey::publicKey() const
 
     stream.writeString(m_type);
 
-    for (QByteArray ba : m_publicData) {
+    for (const QByteArray& ba : m_publicData) {
         stream.writeString(ba);
     }
 
@@ -544,7 +544,7 @@ bool OpenSSHKey::writePublic(BinaryStream& stream)
         return false;
     }
 
-    for (QByteArray t : m_publicData) {
+    for (const QByteArray& t : m_publicData) {
         if (!stream.writeString(t)) {
             m_error = tr("Unexpected EOF when writing public key");
             return false;
@@ -566,7 +566,7 @@ bool OpenSSHKey::writePrivate(BinaryStream& stream)
         return false;
     }
 
-    for (QByteArray t : m_privateData) {
+    for (const QByteArray& t : m_privateData) {
         if (!stream.writeString(t)) {
             m_error = tr("Unexpected EOF when writing private key");
             return false;
diff --git a/src/sshagent/SSHAgent.cpp b/src/sshagent/SSHAgent.cpp
index 758c86851..487398238 100644
--- a/src/sshagent/SSHAgent.cpp
+++ b/src/sshagent/SSHAgent.cpp
@@ -38,7 +38,7 @@ SSHAgent::SSHAgent(QObject* parent)
 
 SSHAgent::~SSHAgent()
 {
-    for (QSet<OpenSSHKey> keys : m_keys.values()) {
+    for (const QSet<OpenSSHKey>& keys : m_keys.values()) {
         for (OpenSSHKey key : keys) {
             removeIdentity(key);
         }
diff --git a/src/streams/HmacBlockStream.cpp b/src/streams/HmacBlockStream.cpp
index 780db98c1..30c7bac5e 100644
--- a/src/streams/HmacBlockStream.cpp
+++ b/src/streams/HmacBlockStream.cpp
@@ -17,6 +17,8 @@
 
 #include "HmacBlockStream.h"
 
+#include <utility>
+
 #include "core/Endian.h"
 #include "crypto/CryptoHash.h"
 
@@ -25,7 +27,7 @@ const QSysInfo::Endian HmacBlockStream::ByteOrder = QSysInfo::LittleEndian;
 HmacBlockStream::HmacBlockStream(QIODevice* baseDevice, QByteArray key)
     : LayeredStream(baseDevice)
     , m_blockSize(1024 * 1024)
-    , m_key(key)
+    , m_key(std::move(key))
 {
     init();
 }
@@ -33,7 +35,7 @@ HmacBlockStream::HmacBlockStream(QIODevice* baseDevice, QByteArray key)
 HmacBlockStream::HmacBlockStream(QIODevice* baseDevice, QByteArray key, qint32 blockSize)
     : LayeredStream(baseDevice)
     , m_blockSize(blockSize)
-    , m_key(key)
+    , m_key(std::move(key))
 {
     init();
 }
@@ -245,7 +247,7 @@ QByteArray HmacBlockStream::getCurrentHmacKey() const
     return getHmacKey(m_blockIndex, m_key);
 }
 
-QByteArray HmacBlockStream::getHmacKey(quint64 blockIndex, QByteArray key)
+QByteArray HmacBlockStream::getHmacKey(quint64 blockIndex, const QByteArray& key)
 {
     Q_ASSERT(key.size() == 64);
     QByteArray indexBytes = Endian::sizedIntToBytes<quint64>(blockIndex, ByteOrder);
diff --git a/src/streams/HmacBlockStream.h b/src/streams/HmacBlockStream.h
index c10c96746..a2ad062e3 100644
--- a/src/streams/HmacBlockStream.h
+++ b/src/streams/HmacBlockStream.h
@@ -34,7 +34,7 @@ public:
     bool reset() override;
     void close() override;
 
-    static QByteArray getHmacKey(quint64 blockIndex, QByteArray key);
+    static QByteArray getHmacKey(quint64 blockIndex, const QByteArray& key);
 
     bool atEnd() const override;
 
diff --git a/src/streams/qtiocompressor.cpp b/src/streams/qtiocompressor.cpp
index 97955e472..6e3c69ffc 100644
--- a/src/streams/qtiocompressor.cpp
+++ b/src/streams/qtiocompressor.cpp
@@ -116,7 +116,7 @@ QtIOCompressorPrivate::~QtIOCompressorPrivate()
 void QtIOCompressorPrivate::flushZlib(int flushMode)
 {
     // No input.
-    zlibStream.next_in = 0;
+    zlibStream.next_in = nullptr;
     zlibStream.avail_in = 0;
     int status;
     do {
@@ -387,7 +387,7 @@ bool QtIOCompressor::open(OpenMode mode)
     if (read) {
         d->state = QtIOCompressorPrivate::NotReadFirstByte;
         d->zlibStream.avail_in = 0;
-        d->zlibStream.next_in = 0;
+        d->zlibStream.next_in = nullptr;
         if (d->streamFormat == QtIOCompressor::ZlibFormat) {
             status = inflateInit(&d->zlibStream);
         } else {
diff --git a/src/totp/totp.cpp b/src/totp/totp.cpp
index 4140993c7..f1146441a 100644
--- a/src/totp/totp.cpp
+++ b/src/totp/totp.cpp
@@ -97,7 +97,7 @@ QSharedPointer<Totp::Settings> Totp::createSettings(const QString& key, const ui
     });
 }
 
-QString Totp::writeSettings(const QSharedPointer<Totp::Settings> settings, const QString& title, const QString& username, bool forceOtp)
+QString Totp::writeSettings(const QSharedPointer<Totp::Settings>& settings, const QString& title, const QString& username, bool forceOtp)
 {
     if (settings.isNull()) {
         return {};
@@ -106,9 +106,9 @@ QString Totp::writeSettings(const QSharedPointer<Totp::Settings> settings, const
     // OTP Url output
     if (settings->otpUrl || forceOtp) {
         auto urlstring = QString("otpauth://totp/%1:%2?secret=%3&period=%4&digits=%5&issuer=%1")
-                .arg(title.isEmpty() ? "KeePassXC" : QString(QUrl::toPercentEncoding(title)))
-                .arg(username.isEmpty() ? "none" : QString(QUrl::toPercentEncoding(username)))
-                .arg(QString(Base32::sanitizeInput(settings->key.toLatin1())))
+                .arg(title.isEmpty() ? "KeePassXC" : QString(QUrl::toPercentEncoding(title)),
+                     username.isEmpty() ? "none" : QString(QUrl::toPercentEncoding(username)),
+                     QString(Base32::sanitizeInput(settings->key.toLatin1())))
                 .arg(settings->step)
                 .arg(settings->digits);
 
@@ -127,7 +127,7 @@ QString Totp::writeSettings(const QSharedPointer<Totp::Settings> settings, const
     return QString("%1;%2").arg(settings->step).arg(settings->digits);
 }
 
-QString Totp::generateTotp(const QSharedPointer<Totp::Settings> settings, const quint64 time)
+QString Totp::generateTotp(const QSharedPointer<Totp::Settings>& settings, const quint64 time)
 {
     Q_ASSERT(!settings.isNull());
     if (settings.isNull()) {
@@ -194,7 +194,7 @@ Totp::Encoder& Totp::steamEncoder()
     return getEncoderByShortName("S");
 }
 
-Totp::Encoder& Totp::getEncoderByShortName(QString shortName)
+Totp::Encoder& Totp::getEncoderByShortName(const QString& shortName)
 {
     for (auto& encoder : encoders) {
         if (encoder.shortName == shortName) {
@@ -204,7 +204,7 @@ Totp::Encoder& Totp::getEncoderByShortName(QString shortName)
     return defaultEncoder();
 }
 
-Totp::Encoder& Totp::getEncoderByName(QString name)
+Totp::Encoder& Totp::getEncoderByName(const QString& name)
 {
     for (auto& encoder : encoders) {
         if (encoder.name == name) {
diff --git a/src/totp/totp.h b/src/totp/totp.h
index ba11ba2b0..0697281bf 100644
--- a/src/totp/totp.h
+++ b/src/totp/totp.h
@@ -60,15 +60,15 @@ static const QString ATTRIBUTE_SETTINGS = "TOTP Settings";
 QSharedPointer<Totp::Settings> parseSettings(const QString& rawSettings, const QString& key = {});
 QSharedPointer<Totp::Settings> createSettings(const QString& key, const uint digits, const uint step,
                                               const QString& encoderShortName = {});
-QString writeSettings(const QSharedPointer<Totp::Settings> settings, const QString& title = {},
+QString writeSettings(const QSharedPointer<Totp::Settings>& settings, const QString& title = {},
                       const QString& username = {}, bool forceOtp = false);
 
-QString generateTotp(const QSharedPointer<Totp::Settings> settings, const quint64 time = 0ull);
+QString generateTotp(const QSharedPointer<Totp::Settings>& settings, const quint64 time = 0ull);
 
 Encoder& defaultEncoder();
 Encoder& steamEncoder();
-Encoder& getEncoderByShortName(QString shortName);
-Encoder& getEncoderByName(QString name);
+Encoder& getEncoderByShortName(const QString& shortName);
+Encoder& getEncoderByName(const QString& name);
 }
 
 #endif // QTOTP_H