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.
/***************************************************************************/
/* */
/* t1driver.h */
/* */
/* High-level Type 1 driver interface (specification). */
/* */
/* Copyright 1996-2001, 2002 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. */
/* */
/***************************************************************************/
#ifndef __T1DRIVER_H__
#define __T1DRIVER_H__
#include <ft2build.h>
#include FT_INTERNAL_DRIVER_H
FT_BEGIN_HEADER
#ifdef FT_CONFIG_OPTION_PIC
#error "this module does not support PIC yet"
#endif
FT_EXPORT_VAR( const FT_Driver_ClassRec ) t1_driver_class;
FT_END_HEADER
#endif /* __T1DRIVER_H__ */
/* END */