QLineEdit is a component of the Qt library which is basically a text editor that has only one line, and which allows one to make inputting and editing of text. A related class is QTextEdit which allows multi-line, rich text editing.
A minimalistic example of a QLineEdit that is shown in a new window, and contains the infamous "Hello, World!" line:
#include <QtGui>
#include <QApplication>
int main(int argc, char *argv[])
{
QApplication a( argc, argv );
QLineEdit * myLine = new QLineEdit( "Hello, World!" );
myLine->show();
return a.exec();
}
The official Qt documentation can be found here for Qt 4.8 and here for Qt 5.
