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.
/***************************************************************************/
/* */
/* type1.c */
/* */
/* FreeType Type 1 driver component (body only). */
/* */
/* Copyright 1996-2001 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. */
/* */
/***************************************************************************/
#define FT_MAKE_OPTION_SINGLE_OBJECT
#include <ft2build.h>
#include "t1parse.c"
#include "t1load.c"
#include "t1objs.c"
#include "t1driver.c"
#include "t1gload.c"
#ifndef T1_CONFIG_OPTION_NO_AFM
#include "t1afm.c"
#endif
/* END */