What does QObject::connect(buttonBox, SIGNAL(accepted()), this, SLOT(accept())); do in following code

[Qt Enthusiast]

QDialogButtonBox* buttonBox = new QDialogButtonBox();
buttonBox->setStandardButtons(QDialogButtonBox::Apply | QDialogButtonBox::Close);
QPushButton* applyButton = buttonBox->button(QDialogButtonBox::Apply);
QObject::connect(buttonBox, SIGNAL(accepted()), this, SLOT(accept()));

[joeQ]

Hi, friend. Welcome.
The Qt manual said:

[signal] void QDialogButtonBox::accepted()
This signal is emitted when a button inside the button box is clicked, as long as it was defined with the AcceptRole or YesRole.

QDialogButtonBox include more than one button. If there is a AcceptRole button clicked and the signal will be emitted. From the signal, we can know AcceptRole button is clicked in QDialogButtonBox.

eg:

#include "widget.h"
#include "ui_widget.h"

#include <QDialogButtonBox>
#include <QDebug>

Widget::Widget(QWidget *parent) :
    QWidget(parent),
    ui(new Ui::Widget)
{
    ui->setupUi(this);

    QDialogButtonBox *buttonBox = new QDialogButtonBox(QDialogButtonBox::Ok | QDialogButtonBox::Save | QDialogButtonBox::Cancel, this);
    ///< Ok and Save is AcceptRole
    connect(buttonBox, &QDialogButtonBox::accepted, this, [=](){ qDebug("ok or save");     });
    connect(buttonBox, &QDialogButtonBox::rejected, this, [=](){ qDebug("cancel"); });
}

Widget::~Widget()
{
    delete ui;
}

Add the button roles: enum QDialogButtonBox::StandardButton
eg:

QDialogButtonBox::Ok An "OK" button defined with the AcceptRole.
QDialogButtonBox::Open An "Open" button defined with the AcceptRole.
QDialogButtonBox::Save A "Save" button defined with the AcceptRole.
QDialogButtonBox::Cancel A "Cancel" button defined with the RejectRole.
QDialogButtonBox::Close A "Close" button defined with the RejectRole.