シグナルとスロットの接続

$ mkdir quit
$ cd quit
$ vi quit.cpp

#include <QApplication>
#include <QPushButton>

int main(int argc, char *argv[])
{
  QApplication app(argc, argv);
  QPushButton *button = new QPushButton("Quit");
  QObject::connect(button, SIGNAL(clicked()),
                   &app, SLOT(quit()));
  button->show();
  return app.exec();
}

$ qmake -project
$ vi quit.pro

quit.proの最後に「QT += widgets」を追加する。

######################################################################
# Automatically generated by qmake (3.1) Mon May 13 16:36:00 2019
######################################################################

TEMPLATE = app
TARGET = quit
INCLUDEPATH += .

# The following define makes your compiler warn you if you use any
# feature of Qt which has been marked as deprecated (the exact warnings
# depend on your compiler). Please consult the documentation of the
# deprecated API in order to know how to port your code away from it.
DEFINES += QT_DEPRECATED_WARNINGS

# You can also make your code fail to compile if you use deprecated APIs.
# In order to do so, uncomment the following line.
# You can also select to disable deprecated APIs only up to a certain version of Qt.
#DEFINES += QT_DISABLE_DEPRECATED_BEFORE=0x060000    # disables all the APIs deprecated before Qt 6.
0.0

# Input
SOURCES += quit.cpp
QT += widgets

$ qmake quit.pro
Info: creating stash file /home/nakada/Qt4/quit/.qmake.stash
$ ls
./  ../  .qmake.stash  Makefile  quit.cpp  quit.pro
$ make
g++ -c -pipe -O2 -Wall -W -D_REENTRANT -fPIC -DQT_DEPRECATED_WARNINGS -DQT_NO_DEBUG -DQT_WIDGETS_LIB -DQT_GUI_LIB -DQT_CORE_LIB -I. -I. -isystem /usr/include/x86_64-linux-gnu/qt5 -isystem /usr/include/x86_64-linux-gnu/qt5/QtWidgets -isystem /usr/include/x86_64-linux-gnu/qt5/QtGui -isystem /usr/include/x86_64-linux-gnu/qt5/QtCore -I. -isystem /usr/include/libdrm -I/usr/lib/x86_64-linux-gnu/qt5/mkspecs/linux-g++ -o quit.o quit.cpp
g++ -Wl,-O1 -o quit quit.o   -lQt5Widgets -lQt5Gui -lQt5Core /usr/lib/x86_64-linux-gnu/libGL.so -lpthread
$ ls
./  ../  .qmake.stash  Makefile  quit*  quit.cpp  quit.o  quit.pro
$ ./quit

Quitボタンをクリックすると終了する。