Chapter 1: Hello, World!

目次

1. ソースコード
2. 解説
3. コンパイル・動作確認
4. いじくりまわす

ソースコード

/****************************************************************
**
** Qt tutorial 1
**
****************************************************************/

#include <qapplication.h>
#include <qpushbutton.h>

int main( int argc, char **argv )
{
    QApplication a( argc, argv );

    QPushButton hello( "Hello world!", 0 );
    hello.resize( 100, 30 );

    a.setMainWidget( &hello );
    hello.show();
    return a.exec();
}

解説

	#include <qapplication.h>

	#include <qpushbutton.h>

int main( int argc, char **argv )
    {

        QApplication a( argc, argv );

 Note that all command-line arguments recognized by Qt are removed from argv (and argc is decremented accordingly).

Example:

    // showargs.cpp - displays program arguments in a list box

    #include <qapplication.h>
    #include <qlistbox.h>

    int main( int argc, char **argv )
    {
        QApplication a( argc, argv );
        QListBox b;
        a.setMainWidget( &b );
        for ( int i=0; i<a.argc(); i++ )        // a.argc() == argc
            b.insertItem( a.argv()[i] );        // a.argv()[i] == argv[i]
        b.show();
        return a.exec();
    }

        QPushButton hello( "Hello world!", 0 );

QPushButton::QPushButton ( const QString & text, QWidget * parent, const char * name=0 )

        hello.resize( 100, 30 );

        a.setMainWidget( &hello );

        hello.show();

        return a.exec();
}

 Enters the main event loop and waits until exit() is called or the main widget is destroyed,
and Returns the value that was set via to exit() (which is 0 if exit() is called via quit()).
 It is necessary to call this function to start event handling.
 The main event loop receives events from the window system and dispatches these to the application widgets.

 Generally speaking, no user interaction can take place before calling exec().
As a special case, modal widgets like QMessageBox can be used before calling exec(),
because modal widgets call exec() to start a local event loop.

 To make your application perform idle processing, i.e. executing a special function whenever there are no
pending events, use a QTimer with 0 timeout.
  More advanced idle processing schemes can be achieved by using processEvents() and processOneEvent().
This is where main() passes control to Qt. exec() will return when the application exits.

コンパイル・動作確認

[fenjin@seisyuu qt_tutorials]$ ls
t01/
[fenjin@seisyuu qt_tutorials]$ cd t01/
[fenjin@seisyuu t01]$ ls
t01.cpp
[fenjin@seisyuu t01]$ progen -n t01 -o t01.pro
[fenjin@seisyuu t01]$ ls
t01.cpp  t01.pro
[fenjin@seisyuu t01]$ tmake -o Makefile t01.pro
[fenjin@seisyuu t01]$ ls
Makefile  t01.cpp  t01.pro
[fenjin@seisyuu t01]$ make
g++ -c -pipe -Wall -W -O2 -DNO_DEBUG -I/usr/lib/qt/include -o t01.o t01.cpp
g++  -o t01 t01.o   -L/usr/lib/qt/lib -L/usr/X11R6/lib -lqt -lXext -lX11 -lm
[fenjin@seisyuu t01]$ ls
Makefile  t01*  t01.cpp  t01.o  t01.pro

いじくりまわす

void QApplication::setMainWidget ( QWidget * mainWidget ) [virtual]

 Sets the main widget of the application.
 The main widget is like any other, in most respects except
that if it is deleted, the application exits.
 You need not have a main widget; connecting lastWindowClosed()
to quit() is another alternative.
 For X11, this function also resizes and moves the main widget
according to the -geometry command-line option, so you should
set the default geometry (using QWidget::setGeometry()) before
calling setMainWidget().

修正前：

   a.setMainWidget(&hello);
   hello.show();

修正後：

    //a.setMainWidget(&hello);
    a.connect(&a, SIGNAL(lastWindowClosed()), SLOT(quit()));
    hello.show();

[fenjin@seisyuu yorimichi01]$ vi listargv.cpp
[fenjin@seisyuu yorimichi01]$ ls
listargv.cpp
[fenjin@seisyuu yorimichi01]$ progen -n listargv -o listargv.pro
[fenjin@seisyuu yorimichi01]$ tmake -o Makefile listargv.pro
[fenjin@seisyuu yorimichi01]$ ls
Makefile  listargv.cpp  listargv.pro
[fenjin@seisyuu yorimichi01]$ make
g++ -c -pipe -Wall -W -O2 -DNO_DEBUG -I/usr/lib/qt/include -o listargv.o listargv.cpp
g++  -o listargv listargv.o   -L/usr/lib/qt/lib -L/usr/X11R6/lib -lqt -lXext -lX11 -lm
[fenjin@seisyuu yorimichi01]$ ./listargv --help --hogehoge -foo-bar