set( filename "build-number.txt" )

# check for the previous build number
if ( EXISTS "${filename}" )
	# read build number from file
	file( READ "${filename}" build_number LIMIT 10 )
else()
	# no file with build number, assuming very first build
	set( build_number 0 )
endif()

# increment build number
math( EXPR build_number "${build_number} + 1" )

# save new build number into the same file
file( WRITE "${filename}" "${build_number}" )

cmake_minimum_required( VERSION 2.8 )

find_package( Qt4 REQUIRED )
include( "${QT_USE_FILE}" )

add_executable( test main.cpp )
target_link_libraries( test ${QT_LIBRARIES} )

# add target that will increment build number
add_custom_target( increment ALL
	"${CMAKE_COMMAND}" -E chdir "${CMAKE_CURRENT_SOURCE_DIR}" "${CMAKE_COMMAND}" -P "increment.cmake"
)

add_dependencies( test increment )

C++ (Qt)
 
#include <QApplication>
#include <QWidget>
#include <QFile>
#include <QTextStream>
 
int main( int argc, char ** argv )
{
	QApplication app( argc, argv );
 
	// read build number
	int buildNumber = -1;
	{
		QFile file( "build-number.txt" );
		if ( file.open( QIODevice::ReadOnly ) )
		{
			QTextStream ts( &file );
			const QString buildNumberString = ts.readLine();
			bool ok;
			const int readBuildNumber = buildNumberString.toInt( &ok );
			if ( ok )
				buildNumber = readBuildNumber;
		}
	}
 
	const QString BuildNumberTemplate = QString( "Build number: %1" );
	const QString title = buildNumber == -1 ?
		BuildNumberTemplate.arg( "Unknown" ) :
		BuildNumberTemplate.arg( buildNumber );
 
	QWidget w;
	w.setWindowTitle( title );
	w.show();
 
	return app.exec();
}
 

#define _RELEASE_BUILD_NUMBER_ ${build_number}

...
# generate header with build version
configure_file( "build_number.h.template" "build_number.h" )

C++ (Qt)
#include <QApplication>
#include <QWidget>
 
#include "build_number.h"
 
int main( int argc, char ** argv )
{
	QApplication app( argc, argv );
 
	QWidget w;
	w.setWindowTitle( QString( "Build number: %1" ).arg( _RELEASE_BUILD_NUMBER_ ) );
	w.show();
 
	return app.exec();
}