passing by reference... my darkest enemy
actual reason below:
In your case (without reference) the compiler generates a temporary object (int) for the first argument of your MyApplication constructor. You pass this temporary int to QApplication’s constructor (with int reference), which saves the address of this reference. Once your MyApplication constructor is done the temporary int is destroyed but QApplication still has its address.
/***************************************************************************/
/* */
/* ft2build.h */
/* */
/* FreeType 2 build and setup macros. */
/* (Generic version) */
/* */
/* Copyright 1996-2001, 2003, 2006 by */
/* David Turner, Robert Wilhelm, and Werner Lemberg. */
/* */
/* This file is part of the FreeType project, and may only be used, */
/* modified, and distributed under the terms of the FreeType project */
/* license, LICENSE.TXT. By continuing to use, modify, or distribute */
/* this file you indicate that you have read the license and */
/* understand and accept it fully. */
/* */
/***************************************************************************/
/*
* This is a development version of <ft2build.h> that is used
* to build the library in debug mode. Its only difference with
* the reference is that it forces the use of the local `ftoption.h'
* which contains different settings for all configuration macros.
*
* To use it, you must define the environment variable FT2_BUILD_INCLUDE
* to point to the directory containing these two files (`ft2build.h' and
* `ftoption.h'), then invoke Jam as usual.
*/
#ifndef __FT2_BUILD_DEVEL_H__
#define __FT2_BUILD_DEVEL_H__
#define FT_CONFIG_OPTIONS_H <ftoption.h>
#include <freetype/config/ftheader.h>
#endif /* __FT2_BUILD_DEVEL_H__ */
/* END */