Qt 对话框里添加确定取消按钮

QDialog  dialog;
dialog.setWindowTitle(tr("选择要保存的格式"));

QComboBox *box = new QComboBox(&dialog);
box->addItem("jpg");
box->addItem("bmp");
box->addItem("png");
box->addItem("tif");
box->addItem("img");

QDialogButtonBox *button = new QDialogButtonBox(&dialog);
button->addButton( "OK", QDialogButtonBox::YesRole);
button->addButton( "NO", QDialogButtonBox::NoRole);
connect(button, SIGNAL(accepted()), &dialog, SLOT(accept()));
connect(button, SIGNAL(rejected()), &dialog, SLOT(reject()));

QVBoxLayout *layout = new QVBoxLayout;
layout->addWidget(box);
layout->addWidget( button);
dialog.setLayout(layout);

QString suffix ;
if ( dialog.exec() == QDialog::Accepted)
{

suffix = box->currentText();
ImageConvert img;
img.ConvertImages( files, dstpath.toStdString(), suffix.toStdString());
}