In QMessageBox, how do I add to the text copied by Ctrl-C?

Using Qt, C++ on Windows, Ctrl-C copies a selection of text that includes the title, message, and so forth from a QMessageBox. I have added some additional fields and would like to add some custom text to the information copied from the standard QMessageBox from these fields. What do I override in QMessageBox to allow me to grab the text that is already being created and add my own text to it?

You need to reimplement QMessageBox and all functions you want to use. Here is minimal example:

custommessagebox.h

#include <QMessageBox>
#include <QShortcut>

class CustomMessageBox : public QMessageBox
{
    Q_OBJECT
public:
    explicit CustomMessageBox(QWidget *parent = 0);
    CustomMessageBox(Icon icon, const QString &title, const QString &text,
                StandardButtons buttons = NoButton, QWidget *parent = Q_NULLPTR,
                Qt::WindowFlags flags = Qt::Dialog | Qt::MSWindowsFixedSizeDialogHint);
    static StandardButton information(QWidget *parent, const QString &title,
         const QString &text, StandardButtons buttons = Ok,
         StandardButton defaultButton = NoButton);

protected:
    void keyPressEvent(QKeyEvent *e);
};

custommessagebox.cpp

#include "custommessagebox.h"
#include <QClipboard>
#include <QApplication>
#include <QKeyEvent>
#include <QDialogButtonBox>

static QMessageBox::StandardButton showNewMessageBox(QWidget *parent,
    QMessageBox::Icon icon,
    const QString& title, const QString& text,
    QMessageBox::StandardButtons buttons,
    QMessageBox::StandardButton defaultButton)
{
    CustomMessageBox msgBox(icon, title, text, QMessageBox::NoButton, parent);
    QDialogButtonBox *buttonBox = msgBox.findChild<QDialogButtonBox*>();
    Q_ASSERT(buttonBox != 0);

    uint mask = QMessageBox::FirstButton;
    while (mask <= QMessageBox::LastButton) {
        uint sb = buttons & mask;
        mask <<= 1;
        if (!sb)
            continue;
        QPushButton *button = msgBox.addButton((QMessageBox::StandardButton)sb);
        // Choose the first accept role as the default
        if (msgBox.defaultButton())
            continue;
        if ((defaultButton == QMessageBox::NoButton && buttonBox->buttonRole((QAbstractButton*)button) == QDialogButtonBox::AcceptRole)
            || (defaultButton != QMessageBox::NoButton && sb == uint(defaultButton)))
            msgBox.setDefaultButton(button);
    }
    if (msgBox.exec() == -1)
        return QMessageBox::Cancel;
    return msgBox.standardButton(msgBox.clickedButton());
}

CustomMessageBox::CustomMessageBox(QWidget *parent) : QMessageBox(parent)
{

}

CustomMessageBox::CustomMessageBox(QMessageBox::Icon icon, const QString &title, const QString &text, QMessageBox::StandardButtons buttons, QWidget *parent, Qt::WindowFlags flags)
 : QMessageBox(icon, title, text, buttons, parent, flags)
{

}

void CustomMessageBox::keyPressEvent(QKeyEvent *e)
{
    QMessageBox::keyPressEvent(e);

    if (e == QKeySequence::Copy) {
        QString separator = QString::fromLatin1("---------------------------\n");
        QString tempText = QApplication::clipboard()->text();
        tempText.append("Your custom text.\n" + separator);
        QApplication::clipboard()->setText(tempText);
    }

}

QMessageBox::StandardButton CustomMessageBox::information(QWidget *parent, const QString &title,
                               const QString& text, StandardButtons buttons,
                               StandardButton defaultButton)
{
    return showNewMessageBox(parent, Information, title, text, buttons,
                             defaultButton);
}

Usage:

void MainWindow::showCustomMessage()
{
    CustomMessageBox::information(this, "New message", "A lot of text", 0);
}

Also You might need to override question(), warning(), critical() and some other functions.