In Qt Designer , you can drag a "Line" widget , which will create a line in your layout.
But I checked the document and headers , I didn't find the "Line" header / widget , what was it ?
In Qt 5.7 the code generated by Qt Designer for a Horizontal Line (which can be checked in the menu using "Form/View Code...") is:
QFrame *line;
line = new QFrame(Form);
line->setFrameShape(QFrame::HLine);
line->setFrameShadow(QFrame::Sunken);
This will create the lines you see in Qt Designer.
The current answers do not seem to give working solutions, here is a comparison of all answers (this solution is the first line):
Full code:
#include <QtWidgets>
int main(int argc, char **argv)
{
QApplication app(argc, argv);
QWidget widget;
auto layout = new QVBoxLayout;
widget.setLayout(layout);
widget.resize(200, 200);
auto lineA = new QFrame;
lineA->setFrameShape(QFrame::HLine);
lineA->setFrameShadow(QFrame::Sunken);
layout->addWidget(lineA);
QWidget *lineB = new QWidget;
lineB->setFixedHeight(2);
lineB->setSizePolicy(QSizePolicy::Expanding, QSizePolicy::Fixed);
lineB->setStyleSheet(QString("background-color: #c0c0c0;"));
layout->addWidget(lineB);
auto lineC = new QFrame;
lineC->setFixedHeight(3);
lineC->setFrameShadow(QFrame::Sunken);
lineC->setLineWidth(1);
layout->addWidget(lineC);
QFrame* lineD = new QFrame;
lineD->setFrameShape(QFrame::HLine);
layout->addWidget(lineD);
widget.show();
return app.exec();
}