Merge #15114: Qt: Replace remaining 0 with nullptr

3a0e76fc12b91b2846d756981e15f09b767a9c37 Replace remaining 0 with nullptr in Qt code (Ben Woosley)
9096276e0b2d5b7e19af9a5f3c144ef108ee55e0 Don't use zero as null pointer constant (-Wzero-as-null-pointer-constant) (practicalswift)

Pull request description:

  This corrects all violations of `-Wzero-as-null-pointer-constant` identified in the Qt codebase.

  These changes are extracted from #15112 as suggested by @MarcoFalke to ease review. This is in service of enabling `-Wzero-as-null-pointer-constant`, which should eliminate this as a concern going forward.

  Note there are 2 non-Qt changes: `src/test/allocator_tests.cpp` and `src/wallet/db.cpp`.

Tree-SHA512: 206bd668802147ba42bc413c2d7d259cb59aca9ec1da74a6bf2ca3932e60ae492faacbc61bcee0fd6b4b49a4d59d075b7e5404f0526b36c47718f9b0587e7768

src/qt/addressbookpage.cpp

@@ -61,7 +61,7 @@ protected:
 AddressBookPage::AddressBookPage(Mode _mode, Tabs _tab, QWidget* parent) :
     QDialog(parent),
     ui(new Ui::AddressBookPage),
-    model(0),
+    model(nullptr),
     mode(_mode),
     tab(_tab)
 {

src/qt/addressbookpage.h

@@ -37,7 +37,7 @@ public:
         ForEditing  /**< Open address book for editing */
     };
 
-    explicit AddressBookPage(Mode mode, Tabs tab, QWidget* parent = 0);
+    explicit AddressBookPage(Mode mode, Tabs tab, QWidget* parent = nullptr);
     ~AddressBookPage();
 
     void setModel(AddressTableModel *model);

src/qt/addresstablemodel.cpp

@@ -155,7 +155,7 @@ public:
         }
         else
         {
-            return 0;
+            return nullptr;
         }
     }
 };
@@ -306,8 +306,8 @@ QVariant AddressTableModel::headerData(int section, Qt::Orientation orientation,
 
 Qt::ItemFlags AddressTableModel::flags(const QModelIndex &index) const
 {
-    if(!index.isValid())
-        return 0;
+    if (!index.isValid()) return Qt::NoItemFlags;
+
     AddressTableEntry *rec = static_cast<AddressTableEntry*>(index.internalPointer());
 
     Qt::ItemFlags retval = Qt::ItemIsSelectable | Qt::ItemIsEnabled;

src/qt/addresstablemodel.h

@@ -25,7 +25,7 @@ class AddressTableModel : public QAbstractTableModel
     Q_OBJECT
 
 public:
-    explicit AddressTableModel(WalletModel *parent = 0);
+    explicit AddressTableModel(WalletModel *parent = nullptr);
     ~AddressTableModel();
 
     enum ColumnIndex {

src/qt/askpassphrasedialog.cpp

@@ -24,7 +24,7 @@ AskPassphraseDialog::AskPassphraseDialog(Mode _mode, QWidget *parent) :
     QDialog(parent),
     ui(new Ui::AskPassphraseDialog),
     mode(_mode),
-    model(0),
+    model(nullptr),
     fCapsLock(false)
 {
     ui->setupUi(this);

src/qt/bantablemodel.cpp

@@ -78,7 +78,7 @@ public:
         if (idx >= 0 && idx < cachedBanlist.size())
             return &cachedBanlist[idx];
 
-        return 0;
+        return nullptr;
     }
 };
 
@@ -151,8 +151,7 @@ QVariant BanTableModel::headerData(int section, Qt::Orientation orientation, int
 
 Qt::ItemFlags BanTableModel::flags(const QModelIndex &index) const
 {
-    if(!index.isValid())
-        return 0;
+    if (!index.isValid()) return Qt::NoItemFlags;
 
     Qt::ItemFlags retval = Qt::ItemIsSelectable | Qt::ItemIsEnabled;
     return retval;

src/qt/bantablemodel.h

@@ -45,7 +45,7 @@ class BanTableModel : public QAbstractTableModel
     Q_OBJECT
 
 public:
-    explicit BanTableModel(interfaces::Node& node, ClientModel *parent = 0);
+    explicit BanTableModel(interfaces::Node& node, ClientModel *parent = nullptr);
     ~BanTableModel();
     void startAutoRefresh();
     void stopAutoRefresh();

src/qt/bitcoinamountfield.cpp

@@ -18,7 +18,7 @@
  * return validity.
  * @note Must return 0 if !valid.
  */
-static CAmount parse(const QString &text, int nUnit, bool *valid_out=0)
+static CAmount parse(const QString &text, int nUnit, bool *valid_out= nullptr)
 {
     CAmount val = 0;
     bool valid = BitcoinUnits::parse(nUnit, text, &val);
@@ -87,7 +87,7 @@ public:
         }
     }
 
-    CAmount value(bool *valid_out=0) const
+    CAmount value(bool *valid_out=nullptr) const
     {
         return parse(text(), currentUnit, valid_out);
     }
@@ -158,7 +158,7 @@ Q_SIGNALS:
 
 BitcoinAmountField::BitcoinAmountField(QWidget *parent) :
     QWidget(parent),
-    amount(0)
+    amount(nullptr)
 {
     amount = new AmountLineEdit(this);
     amount->setLocale(QLocale::c());

src/qt/bitcoinamountfield.h

@@ -28,9 +28,9 @@ class BitcoinAmountField: public QWidget
     Q_PROPERTY(qint64 value READ value WRITE setValue NOTIFY valueChanged USER true)
 
 public:
-    explicit BitcoinAmountField(QWidget *parent = 0);
+    explicit BitcoinAmountField(QWidget *parent = nullptr);
 
-    CAmount value(bool *value=0) const;
+    CAmount value(bool *value=nullptr) const;
     void setValue(const CAmount& value);
 
     /** Make read-only **/

src/qt/bitcoingui.cpp

@@ -1697,7 +1697,7 @@ void BitcoinGUI::updateProxyIcon()
     bool proxy_enabled = clientModel->getProxyInfo(ip_port);
 
     if (proxy_enabled) {
-        if (labelProxyIcon->pixmap() == 0) {
+        if (labelProxyIcon->pixmap() == nullptr) {
             QString ip_port_q = QString::fromStdString(ip_port);
             labelProxyIcon->setPixmap(GUIUtil::getIcon("proxy", GUIUtil::ThemedColor::GREEN).pixmap(STATUSBAR_ICONSIZE, STATUSBAR_ICONSIZE));
             labelProxyIcon->setToolTip(tr("Proxy is <b>enabled</b>: %1").arg(ip_port_q));
@@ -1743,7 +1743,7 @@ void BitcoinGUI::showProgress(const QString &title, int nProgress)
         progressDialog = new QProgressDialog(title, "", 0, 100, this);
         progressDialog->setWindowModality(Qt::ApplicationModal);
         progressDialog->setMinimumDuration(0);
-        progressDialog->setCancelButton(0);
+        progressDialog->setCancelButton(nullptr);
         progressDialog->setAutoClose(false);
         progressDialog->setValue(0);
     }
@@ -1818,8 +1818,8 @@ void BitcoinGUI::handleRestart(QStringList args)
 }
 
 UnitDisplayStatusBarControl::UnitDisplayStatusBarControl() :
-    optionsModel(0),
-    menu(0)
+    optionsModel(nullptr),
+    menu(nullptr)
 {
     createContextMenu();
     setToolTip(tr("Unit to show amounts in. Click to select another unit."));

src/qt/bitcoingui.h

@@ -67,7 +67,7 @@ class BitcoinGUI : public QMainWindow
 public:
     static const std::string DEFAULT_UIPLATFORM;
 
-    explicit BitcoinGUI(interfaces::Node& node, const NetworkStyle* networkStyle, QWidget* parent = 0);
+    explicit BitcoinGUI(interfaces::Node& node, const NetworkStyle* networkStyle, QWidget* parent = nullptr);
     ~BitcoinGUI();
 
     /** Set the client model.

src/qt/clientmodel.cpp

@@ -38,9 +38,9 @@ ClientModel::ClientModel(interfaces::Node& node, OptionsModel *_optionsModel, QO
     QObject(parent),
     m_node(node),
     optionsModel(_optionsModel),
-    peerTableModel(0),
-    banTableModel(0),
-    pollTimer(0)
+    peerTableModel(nullptr),
+    banTableModel(nullptr),
+    pollTimer(nullptr)
 {
     cachedBestHeaderHeight = -1;
     cachedBestHeaderTime = -1;

src/qt/clientmodel.h

@@ -48,7 +48,7 @@ class ClientModel : public QObject
     Q_OBJECT
 
 public:
-    explicit ClientModel(interfaces::Node& node, OptionsModel *optionsModel, QObject *parent = 0);
+    explicit ClientModel(interfaces::Node& node, OptionsModel *optionsModel, QObject *parent = nullptr);
     ~ClientModel();
 
     interfaces::Node& node() const { return m_node; }

src/qt/coincontroltreewidget.h

@@ -13,7 +13,7 @@ class CoinControlTreeWidget : public QTreeWidget
     Q_OBJECT
 
 public:
-    explicit CoinControlTreeWidget(QWidget *parent = 0);
+    explicit CoinControlTreeWidget(QWidget *parent = nullptr);
 
 protected:
     virtual void keyPressEvent(QKeyEvent *event) override;

src/qt/csvmodelwriter.cpp

@@ -10,7 +10,7 @@
 
 CSVModelWriter::CSVModelWriter(const QString &_filename, QObject *parent) :
     QObject(parent),
-    filename(_filename), model(0)
+    filename(_filename), model(nullptr)
 {
 }
 

src/qt/csvmodelwriter.h

@@ -20,7 +20,7 @@ class CSVModelWriter : public QObject
     Q_OBJECT
 
 public:
-    explicit CSVModelWriter(const QString &filename, QObject *parent = 0);
+    explicit CSVModelWriter(const QString &filename, QObject *parent = nullptr);
 
     void setModel(const QAbstractItemModel *model);
     void addColumn(const QString &title, int column, int role=Qt::EditRole);

src/qt/dash.cpp

@@ -294,14 +294,14 @@ void BitcoinCore::shutdown()
 
 BitcoinApplication::BitcoinApplication(interfaces::Node& node, int &argc, char **argv):
     QApplication(argc, argv),
-    coreThread(0),
+    coreThread(nullptr),
     m_node(node),
-    optionsModel(0),
-    clientModel(0),
-    window(0),
-    pollShutdownTimer(0),
+    optionsModel(nullptr),
+    clientModel(nullptr),
+    window(nullptr),
+    pollShutdownTimer(nullptr),
 #ifdef ENABLE_WALLET
-    paymentServer(0),
+    paymentServer(nullptr),
     m_wallet_models(),
 #endif
     returnValue(0)
@@ -320,10 +320,10 @@ BitcoinApplication::~BitcoinApplication()
     }
 
     delete window;
-    window = 0;
+    window = nullptr;
 #ifdef ENABLE_WALLET
     delete paymentServer;
-    paymentServer = 0;
+    paymentServer = nullptr;
 #endif
     // Delete Qt-settings if user clicked on "Reset Options"
     QSettings settings;
@@ -332,7 +332,7 @@ BitcoinApplication::~BitcoinApplication()
         settings.sync();
     }
     delete optionsModel;
-    optionsModel = 0;
+    optionsModel = nullptr;
 }
 
 #ifdef ENABLE_WALLET
@@ -349,14 +349,14 @@ void BitcoinApplication::createOptionsModel(bool resetSettings)
 
 void BitcoinApplication::createWindow(const NetworkStyle *networkStyle)
 {
-    window = new BitcoinGUI(m_node, networkStyle, 0);
+    window = new BitcoinGUI(m_node, networkStyle, nullptr);
     pollShutdownTimer = new QTimer(window);
     connect(pollShutdownTimer, &QTimer::timeout, window, &BitcoinGUI::detectShutdown);
 }
 
 void BitcoinApplication::createSplashScreen(const NetworkStyle *networkStyle)
 {
-    SplashScreen *splash = new SplashScreen(m_node, 0, networkStyle);
+    SplashScreen *splash = new SplashScreen(m_node, nullptr, networkStyle);
     // We don't hold a direct pointer to the splash screen after creation, but the splash
     // screen will take care of deleting itself when slotFinish happens.
     splash->show();
@@ -413,7 +413,7 @@ void BitcoinApplication::requestShutdown()
     qDebug() << __func__ << ": Requesting shutdown";
     startThread();
     window->hide();
-    window->setClientModel(0);
+    window->setClientModel(nullptr);
     pollShutdownTimer->stop();
 
 #ifdef ENABLE_WALLET
@@ -424,7 +424,7 @@ void BitcoinApplication::requestShutdown()
     m_wallet_models.clear();
 #endif
     delete clientModel;
-    clientModel = 0;
+    clientModel = nullptr;
 
     m_node.startShutdown();
 
@@ -526,7 +526,7 @@ void BitcoinApplication::shutdownResult()
 
 void BitcoinApplication::handleRunawayException(const QString &message)
 {
-    QMessageBox::critical(0, "Runaway exception", BitcoinGUI::tr("A fatal error occurred. Dash Core can no longer continue safely and will quit.") + QString("\n\n") + message);
+    QMessageBox::critical(nullptr, "Runaway exception", BitcoinGUI::tr("A fatal error occurred. Dash Core can no longer continue safely and will quit.") + QString("\n\n") + message);
     ::exit(EXIT_FAILURE);
 }
 
@@ -608,7 +608,7 @@ int main(int argc, char *argv[])
     SetupUIArgs();
     std::string error;
     if (!node->parseParameters(argc, argv, error)) {
-        QMessageBox::critical(0, QObject::tr(PACKAGE_NAME),
+        QMessageBox::critical(nullptr, QObject::tr(PACKAGE_NAME),
             QObject::tr("Error parsing command line arguments: %1.").arg(QString::fromStdString(error)));
         return EXIT_FAILURE;
     }
@@ -649,12 +649,12 @@ int main(int argc, char *argv[])
     /// - Do not call GetDataDir(true) before this step finishes
     if (!fs::is_directory(GetDataDir(false)))
     {
-        QMessageBox::critical(0, QObject::tr(PACKAGE_NAME),
-                              QObject::tr("Error: Specified data directory \"%1\" does not exist.").arg(QString::fromStdString(gArgs.GetArg("-datadir", ""))));
+        QMessageBox::critical(nullptr, QObject::tr(PACKAGE_NAME),
+            QObject::tr("Error: Specified data directory \"%1\" does not exist.").arg(QString::fromStdString(gArgs.GetArg("-datadir", ""))));
         return EXIT_FAILURE;
     }
     if (!node->readConfigFiles(error)) {
-        QMessageBox::critical(0, QObject::tr(PACKAGE_NAME),
+        QMessageBox::critical(nullptr, QObject::tr(PACKAGE_NAME),
             QObject::tr("Error: Cannot parse configuration file: %1.").arg(QString::fromStdString(error)));
         return EXIT_FAILURE;
     }
@@ -669,7 +669,7 @@ int main(int argc, char *argv[])
     try {
         node->selectParams(gArgs.GetChainName());
     } catch(std::exception &e) {
-        QMessageBox::critical(0, QObject::tr(PACKAGE_NAME), QObject::tr("Error: %1").arg(e.what()));
+        QMessageBox::critical(nullptr, QObject::tr(PACKAGE_NAME), QObject::tr("Error: %1").arg(e.what()));
         return EXIT_FAILURE;
     }
 #ifdef ENABLE_WALLET

src/qt/editaddressdialog.cpp

@@ -15,9 +15,9 @@
 EditAddressDialog::EditAddressDialog(Mode _mode, QWidget *parent) :
     QDialog(parent),
     ui(new Ui::EditAddressDialog),
-    mapper(0),
+    mapper(nullptr),
     mode(_mode),
-    model(0)
+    model(nullptr)
 {
     ui->setupUi(this);
 

src/qt/editaddressdialog.h

@@ -30,7 +30,7 @@ public:
         EditSendingAddress
     };
 
-    explicit EditAddressDialog(Mode mode, QWidget *parent = 0);
+    explicit EditAddressDialog(Mode mode, QWidget *parent = nullptr);
     ~EditAddressDialog();
 
     void setModel(AddressTableModel *model);

src/qt/guiutil.h

@@ -202,7 +202,7 @@ namespace GUIUtil
         Q_OBJECT
 
     public:
-        explicit ToolTipToRichTextFilter(int size_threshold, QObject *parent = 0);
+        explicit ToolTipToRichTextFilter(int size_threshold, QObject *parent = nullptr);
 
     protected:
         bool eventFilter(QObject *obj, QEvent *evt) override;

src/qt/intro.cpp

@@ -114,7 +114,7 @@ void FreespaceChecker::check()
 Intro::Intro(QWidget *parent, uint64_t blockchain_size, uint64_t chain_state_size) :
     QDialog(parent),
     ui(new Ui::Intro),
-    thread(0),
+    thread(nullptr),
     signalled(false),
     m_blockchain_size(blockchain_size),
     m_chain_state_size(chain_state_size)
@@ -232,7 +232,7 @@ bool Intro::pickDataDirectory(interfaces::Node& node)
                 }
                 break;
             } catch (const fs::filesystem_error&) {
-                QMessageBox::critical(0, tr(PACKAGE_NAME),
+                QMessageBox::critical(nullptr, tr(PACKAGE_NAME),
                     tr("Error: Specified data directory \"%1\" cannot be created.").arg(dataDir));
                 /* fall through, back to choosing screen */
             }
@@ -292,7 +292,7 @@ void Intro::on_dataDirectory_textChanged(const QString &dataDirStr)
 
 void Intro::on_ellipsisButton_clicked()
 {
-    QString dir = QDir::toNativeSeparators(QFileDialog::getExistingDirectory(0, "Choose data directory", ui->dataDirectory->text()));
+    QString dir = QDir::toNativeSeparators(QFileDialog::getExistingDirectory(nullptr, "Choose data directory", ui->dataDirectory->text()));
     if(!dir.isEmpty())
         ui->dataDirectory->setText(dir);
 }

src/qt/intro.h

@@ -30,7 +30,7 @@ class Intro : public QDialog
     Q_OBJECT
 
 public:
-    explicit Intro(QWidget *parent = 0,
+    explicit Intro(QWidget *parent = nullptr,
                    uint64_t blockchain_size = 0, uint64_t chain_state_size = 0);
     ~Intro();
 

src/qt/networkstyle.cpp

@@ -108,5 +108,5 @@ const NetworkStyle *NetworkStyle::instantiate(const QString &networkId)
                     titleAddText.c_str());
         }
     }
-    return 0;
+    return nullptr;
 }

src/qt/optionsdialog.cpp

@@ -34,9 +34,9 @@
 OptionsDialog::OptionsDialog(QWidget *parent, bool enableWallet) :
     QDialog(parent),
     ui(new Ui::OptionsDialog),
-    model(0),
-    mapper(0),
-    pageButtons(0)
+    model(nullptr),
+    mapper(nullptr),
+    pageButtons(nullptr)
 {
     ui->setupUi(this);
 

src/qt/optionsmodel.h

@@ -31,7 +31,7 @@ class OptionsModel : public QAbstractListModel
     Q_OBJECT
 
 public:
-    explicit OptionsModel(interfaces::Node& node, QObject *parent = 0, bool resetSettings = false);
+    explicit OptionsModel(interfaces::Node& node, QObject *parent = nullptr, bool resetSettings = false);
 
     enum OptionID {
         StartAtStartup,         // bool

src/qt/overviewpage.cpp

@@ -112,8 +112,8 @@ OverviewPage::OverviewPage(QWidget* parent) :
     QWidget(parent),
     timer(nullptr),
     ui(new Ui::OverviewPage),
-    clientModel(0),
-    walletModel(0),
+    clientModel(nullptr),
+    walletModel(nullptr),
     cachedNumISLocks(-1),
     txdelegate(new TxViewDelegate(this))
 {

src/qt/overviewpage.h

@@ -29,7 +29,7 @@ class OverviewPage : public QWidget
     Q_OBJECT
 
 public:
-    explicit OverviewPage(QWidget* parent = 0);
+    explicit OverviewPage(QWidget* parent = nullptr);
     ~OverviewPage();
 
     void setClientModel(ClientModel *clientModel);

src/qt/paymentserver.cpp

@@ -292,9 +292,9 @@ bool PaymentServer::ipcSendCommandLine()
 PaymentServer::PaymentServer(QObject* parent, bool startLocalServer) :
     QObject(parent),
     saveURIs(true),
-    uriServer(0),
-    netManager(0),
-    optionsModel(0)
+    uriServer(nullptr),
+    netManager(nullptr),
+    optionsModel(nullptr)
 {
     // Verify that the version of the library that we linked against is
     // compatible with the version of the headers we compiled against.
@@ -317,7 +317,7 @@ PaymentServer::PaymentServer(QObject* parent, bool startLocalServer) :
 
         if (!uriServer->listen(name)) {
             // constructor is called early in init, so don't use "Q_EMIT message()" here
-            QMessageBox::critical(0, tr("Payment request error"),
+            QMessageBox::critical(nullptr, tr("Payment request error"),
                 tr("Cannot start dash: click-to-pay handler"));
         }
         else {

src/qt/peertablemodel.cpp

@@ -99,7 +99,7 @@ public:
         if (idx >= 0 && idx < cachedNodeStats.size())
             return &cachedNodeStats[idx];
 
-        return 0;
+        return nullptr;
     }
 };
 
@@ -107,7 +107,7 @@ PeerTableModel::PeerTableModel(interfaces::Node& node, ClientModel *parent) :
     QAbstractTableModel(parent),
     m_node(node),
     clientModel(parent),
-    timer(0)
+    timer(nullptr)
 {
     columns << tr("NodeId") << tr("Node/Service") << tr("Ping") << tr("Sent") << tr("Received") << tr("User Agent");
     priv.reset(new PeerTablePriv());
@@ -204,8 +204,7 @@ QVariant PeerTableModel::headerData(int section, Qt::Orientation orientation, in
 
 Qt::ItemFlags PeerTableModel::flags(const QModelIndex &index) const
 {
-    if(!index.isValid())
-        return 0;
+    if (!index.isValid()) return Qt::NoItemFlags;
 
     Qt::ItemFlags retval = Qt::ItemIsSelectable | Qt::ItemIsEnabled;
     return retval;

src/qt/peertablemodel.h

@@ -51,7 +51,7 @@ class PeerTableModel : public QAbstractTableModel
     Q_OBJECT
 
 public:
-    explicit PeerTableModel(interfaces::Node& node, ClientModel *parent = 0);
+    explicit PeerTableModel(interfaces::Node& node, ClientModel *parent = nullptr);
     ~PeerTableModel();
     const CNodeCombinedStats *getNodeStats(int idx);
     int getRowByNodeId(NodeId nodeid);

src/qt/qvalidatedlineedit.cpp

@@ -10,7 +10,7 @@
 QValidatedLineEdit::QValidatedLineEdit(QWidget *parent) :
     QLineEdit(parent),
     valid(true),
-    checkValidator(0)
+    checkValidator(nullptr)
 {
     connect(this, &QValidatedLineEdit::textChanged, this, &QValidatedLineEdit::markValid);
 }

src/qt/qvaluecombobox.h

@@ -16,7 +16,7 @@ class QValueComboBox : public QComboBox
     Q_PROPERTY(QVariant value READ value WRITE setValue NOTIFY valueChanged USER true)
 
 public:
-    explicit QValueComboBox(QWidget *parent = 0);
+    explicit QValueComboBox(QWidget *parent = nullptr);
 
     QVariant value() const;
     void setValue(const QVariant &value);

src/qt/receivecoinsdialog.cpp

@@ -22,8 +22,8 @@
 ReceiveCoinsDialog::ReceiveCoinsDialog(QWidget* parent) :
     QDialog(parent),
     ui(new Ui::ReceiveCoinsDialog),
-    columnResizingFixer(0),
-    model(0)
+    columnResizingFixer(nullptr),
+    model(nullptr)
 {
     ui->setupUi(this);
 

src/qt/receivecoinsdialog.h

@@ -38,7 +38,7 @@ public:
         MINIMUM_COLUMN_WIDTH = 130
     };
 
-    explicit ReceiveCoinsDialog(QWidget* parent = 0);
+    explicit ReceiveCoinsDialog(QWidget* parent = nullptr);
     ~ReceiveCoinsDialog();
 
     void setModel(WalletModel *model);

src/qt/receiverequestdialog.cpp

@@ -26,7 +26,7 @@
 #endif
 
 QRImageWidget::QRImageWidget(QWidget *parent):
-    QLabel(parent), contextMenu(0)
+    QLabel(parent), contextMenu(nullptr)
 {
     contextMenu = new QMenu(this);
     QAction *saveImageAction = new QAction(tr("&Save Image..."), this);
@@ -88,7 +88,7 @@ void QRImageWidget::contextMenuEvent(QContextMenuEvent *event)
 ReceiveRequestDialog::ReceiveRequestDialog(QWidget *parent) :
     QDialog(parent),
     ui(new Ui::ReceiveRequestDialog),
-    model(0)
+    model(nullptr)
 {
     ui->setupUi(this);
 

src/qt/receiverequestdialog.h

@@ -28,7 +28,7 @@ class QRImageWidget : public QLabel
     Q_OBJECT
 
 public:
-    explicit QRImageWidget(QWidget *parent = 0);
+    explicit QRImageWidget(QWidget *parent = nullptr);
     QImage exportImage();
 
 public Q_SLOTS:
@@ -48,7 +48,7 @@ class ReceiveRequestDialog : public QDialog
     Q_OBJECT
 
 public:
-    explicit ReceiveRequestDialog(QWidget *parent = 0);
+    explicit ReceiveRequestDialog(QWidget *parent = nullptr);
     ~ReceiveRequestDialog();
 
     void setModel(WalletModel *model);

src/qt/sendcoinsdialog.cpp

@@ -513,7 +513,7 @@ SendCoinsEntry *SendCoinsDialog::addEntry()
 
 void SendCoinsDialog::updateTabsAndLabels()
 {
-    setupTabChain(0);
+    setupTabChain(nullptr);
     coinControlUpdateLabels();
 }
 
@@ -548,7 +548,7 @@ QWidget *SendCoinsDialog::setupTabChain(QWidget *prev)
 
 void SendCoinsDialog::setAddress(const QString &address)
 {
-    SendCoinsEntry *entry = 0;
+    SendCoinsEntry *entry = nullptr;
     // Replace the first entry if it is still unused
     if(ui->entries->count() == 1)
     {
@@ -571,7 +571,7 @@ void SendCoinsDialog::pasteEntry(const SendCoinsRecipient &rv)
     if(!fNewRecipientAllowed)
         return;
 
-    SendCoinsEntry *entry = 0;
+    SendCoinsEntry *entry = nullptr;
     // Replace the first entry if it is still unused
     if(ui->entries->count() == 1)
     {

src/qt/sendcoinsdialog.h

@@ -34,7 +34,7 @@ class SendCoinsDialog : public QDialog
     Q_OBJECT
 
 public:
-    explicit SendCoinsDialog(bool fCoinJoin = false, QWidget* parent = 0);
+    explicit SendCoinsDialog(bool fCoinJoin = false, QWidget* parent = nullptr);
     ~SendCoinsDialog();
 
     void setClientModel(ClientModel *clientModel);
@@ -113,7 +113,7 @@ class SendConfirmationDialog : public QMessageBox
     Q_OBJECT
 
 public:
-    SendConfirmationDialog(const QString &title, const QString &text, int secDelay = 0, QWidget *parent = 0);
+    SendConfirmationDialog(const QString &title, const QString &text, int secDelay = 0, QWidget *parent = nullptr);
     int exec() override;
 
 private Q_SLOTS:

src/qt/sendcoinsentry.cpp

@@ -17,7 +17,7 @@
 SendCoinsEntry::SendCoinsEntry(QWidget* parent) :
     QStackedWidget(parent),
     ui(new Ui::SendCoinsEntry),
-    model(0)
+    model(nullptr)
 {
     ui->setupUi(this);
 
@@ -156,7 +156,7 @@ bool SendCoinsEntry::validate(interfaces::Node& node)
     }
 
     // Sending a zero amount is invalid
-    if (ui->payAmount->value(0) <= 0)
+    if (ui->payAmount->value(nullptr) <= 0)
     {
         ui->payAmount->setValid(false);
         retval = false;

src/qt/sendcoinsentry.h

@@ -25,7 +25,7 @@ class SendCoinsEntry : public QStackedWidget
     Q_OBJECT
 
 public:
-    explicit SendCoinsEntry(QWidget* parent = 0);
+    explicit SendCoinsEntry(QWidget* parent = nullptr);
     ~SendCoinsEntry();
 
     void setModel(WalletModel *model);

src/qt/signverifymessagedialog.cpp

@@ -24,8 +24,8 @@
 SignVerifyMessageDialog::SignVerifyMessageDialog(QWidget* parent) :
     QDialog(parent),
     ui(new Ui::SignVerifyMessageDialog),
-    model(0),
-    pageButtons(0)
+    model(nullptr),
+    pageButtons(nullptr)
 {
     ui->setupUi(this);
 

src/qt/splashscreen.cpp

@@ -28,7 +28,7 @@
 
 
 SplashScreen::SplashScreen(interfaces::Node& node, Qt::WindowFlags f, const NetworkStyle *networkStyle) :
-    QWidget(0, f), curAlignment(0), m_node(node)
+    QWidget(nullptr, f), curAlignment(0), m_node(node)
 {
 
     // transparent background

src/qt/trafficgraphwidget.cpp

@@ -21,10 +21,10 @@
 
 TrafficGraphWidget::TrafficGraphWidget(QWidget *parent) :
     QWidget(parent),
-    timer(0),
+    timer(nullptr),
     fMax(DEFAULT_SAMPLE_HEIGHT),
     nMins(0),
-    clientModel(0),
+    clientModel(nullptr),
     trafficGraphData(TrafficGraphData::Range_30m)
 {
     timer = new QTimer(this);

src/qt/trafficgraphwidget.h

@@ -24,7 +24,7 @@ class TrafficGraphWidget : public QWidget
     Q_OBJECT
 
 public:
-    explicit TrafficGraphWidget(QWidget *parent = 0);
+    explicit TrafficGraphWidget(QWidget *parent = nullptr);
     void setClientModel(ClientModel *model);
     int getGraphRangeMins() const;
 

src/qt/transactiondescdialog.h

@@ -21,7 +21,7 @@ class TransactionDescDialog : public QDialog
     Q_OBJECT
 
 public:
-    explicit TransactionDescDialog(const QModelIndex &idx, QWidget *parent = 0);
+    explicit TransactionDescDialog(const QModelIndex &idx, QWidget *parent = nullptr);
     ~TransactionDescDialog();
 
 private:

src/qt/transactionfilterproxy.h

@@ -16,7 +16,7 @@ class TransactionFilterProxy : public QSortFilterProxyModel
     Q_OBJECT
 
 public:
-    explicit TransactionFilterProxy(QObject *parent = 0);
+    explicit TransactionFilterProxy(QObject *parent = nullptr);
 
     /** Earliest date that can be represented (far in the past) */
     static const QDateTime MIN_DATE;

src/qt/transactiontablemodel.cpp

@@ -204,7 +204,7 @@ public:
             }
             return rec;
         }
-        return 0;
+        return nullptr;
     }
 
     QString describe(interfaces::Node& node, interfaces::Wallet& wallet, TransactionRecord *rec, int unit)

src/qt/transactiontablemodel.h

@@ -27,7 +27,7 @@ class TransactionTableModel : public QAbstractTableModel
     Q_OBJECT
 
 public:
-    explicit TransactionTableModel(WalletModel *parent = 0);
+    explicit TransactionTableModel(WalletModel *parent = nullptr);
     ~TransactionTableModel();
 
     enum ColumnIndex {

src/qt/transactionview.cpp

@@ -44,8 +44,8 @@
 static const char* PERSISTENCE_DATE_FORMAT = "yyyy-MM-dd";
 
 TransactionView::TransactionView(QWidget* parent) :
-    QWidget(parent), model(0), transactionProxyModel(0),
-    transactionView(0), abandonAction(0), columnResizingFixer(0)
+QWidget(parent), model(nullptr), transactionProxyModel(nullptr),
+transactionView(nullptr), abandonAction(nullptr), columnResizingFixer(nullptr)
 {
     QSettings settings;
     // Build filter row

src/qt/transactionview.h

@@ -35,7 +35,7 @@ class TransactionView : public QWidget
     Q_OBJECT
 
 public:
-    explicit TransactionView(QWidget* parent = 0);
+    explicit TransactionView(QWidget* parent = nullptr);
 
     void setModel(WalletModel *model);
 

src/qt/utilitydialog.h

@@ -51,7 +51,7 @@ class ShutdownWindow : public QWidget
     Q_OBJECT
 
 public:
-    explicit ShutdownWindow(interfaces::Node& node, QWidget *parent=0, Qt::WindowFlags f=0);
+    explicit ShutdownWindow(interfaces::Node& node, QWidget *parent=nullptr, Qt::WindowFlags f=Qt::Widget);
     static QWidget *showShutdownWindow(interfaces::Node& node, BitcoinGUI *window);
 
 protected:

src/qt/walletframe.h

@@ -31,7 +31,7 @@ class WalletFrame : public QFrame
     Q_OBJECT
 
 public:
-    explicit WalletFrame(BitcoinGUI* _gui = 0);
+    explicit WalletFrame(BitcoinGUI* _gui = nullptr);
     ~WalletFrame();
 
     void setClientModel(ClientModel *clientModel);

src/qt/walletmodel.cpp

@@ -30,9 +30,9 @@
 
 
 WalletModel::WalletModel(std::unique_ptr<interfaces::Wallet> wallet, interfaces::Node& node, OptionsModel *_optionsModel, QObject *parent) :
-    QObject(parent), m_wallet(std::move(wallet)), m_node(node), optionsModel(_optionsModel), addressTableModel(0),
-    transactionTableModel(0),
-    recentRequestsTableModel(0),
+    QObject(parent), m_wallet(std::move(wallet)), m_node(node), optionsModel(_optionsModel), addressTableModel(nullptr),
+    transactionTableModel(nullptr),
+    recentRequestsTableModel(nullptr),
     cachedEncryptionStatus(Unencrypted),
     cachedNumBlocks(-1),
     cachedNumISLocks(0),

src/qt/walletmodel.h

@@ -102,7 +102,7 @@ class WalletModel : public QObject
     Q_OBJECT
 
 public:
-    explicit WalletModel(std::unique_ptr<interfaces::Wallet> wallet, interfaces::Node& node, OptionsModel *optionsModel, QObject *parent = 0);
+    explicit WalletModel(std::unique_ptr<interfaces::Wallet> wallet, interfaces::Node& node, OptionsModel *optionsModel, QObject *parent = nullptr);
     ~WalletModel();
 
     enum StatusCode // Returned by sendCoins

src/qt/walletview.cpp

@@ -34,8 +34,8 @@
 
 WalletView::WalletView(QWidget* parent) :
     QStackedWidget(parent),
-    clientModel(0),
-    walletModel(0)
+    clientModel(nullptr),
+    walletModel(nullptr)
 {
     // Create tabs
     overviewPage = new OverviewPage();

src/test/allocator_tests.cpp

@@ -105,13 +105,13 @@ BOOST_AUTO_TEST_CASE(arena_tests)
     // Go entirely wild: free and alloc interleaved,
     // generate targets and sizes using pseudo-randomness.
     for (int x=0; x<2048; ++x)
-        addr.push_back(0);
+        addr.push_back(nullptr);
     uint32_t s = 0x12345678;
     for (int x=0; x<5000; ++x) {
         int idx = s & (addr.size()-1);
         if (s & 0x80000000) {
             b.free(addr[idx]);
-            addr[idx] = 0;
+            addr[idx] = nullptr;
         } else if(!addr[idx]) {
             addr[idx] = b.alloc((s >> 16) & 2047);
         }
@@ -146,7 +146,7 @@ public:
 
             return reinterpret_cast<void*>(0x08000000 + (count<<24)); // Fake address, do not actually use this memory
         }
-        return 0;
+        return nullptr;
     }
     void FreeLocked(void* addr, size_t len) override
     {