#include <QApplication>
#include <QDialog>
#include <QDialogButtonBox>
#include <QLineEdit>
#include <QPushButton>
#include <QVBoxLayout>
#include <QWidget>

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    QWidget w;
    w.setLayout(new QVBoxLayout);
    auto button = new QPushButton("Open Dialog");
    w.layout()->addWidget(button);
    QObject::connect(button, &QPushButton::clicked, &w, [&w] {
        QDialog d(&w);
        auto l = new QVBoxLayout;
        d.setLayout(l);
        l->addWidget(new QLineEdit());
        l->addWidget(new QDialogButtonBox(QDialogButtonBox::Ok | QDialogButtonBox::Cancel));
        d.exec();
    });

    w.show();
    return a.exec();
}