c++ - Why is my Qt application crashing when accessing the IWMPMedia interface? -

i have built qt (5.7) application interfaces windows media player com api parse track meta data. in-explicit reason application crashing when calling iwmpmedia3::getattributecountbytype.

the line crash keeps occurring is:

if (pmedia3item && pmedia3item->getattributecountbytype(l"trackingid", 0, &l) == s_ok) //will crash here 

it not crash on first instance, takes couple of hundred loops , seems connected when call repeatedly returns 0. if switch attribute know exists runs fine.

what posted below object stripped right back, still crashes. object designed run in own qthread , com symbols defined , contained within qthread.

the code forms part of larger app makes use of many other qt modules, gui, web engine being 2 of biggest.

#include "wmpmlimport.h" #include <qdebug> #include "wininet.h"  #define wmp_clsid        l"{6bf52a52-394a-11d3-b153-00c04f79faa6}" #define wmp_refiid       l"{d84cca99-cce2-11d2-9ecc-0000f8085981}"  #define wmp_pl_all_music    l"all music"  #define safe_release(ptr) if(null!=(ptr)){(ptr)->release();ptr=null;} #define bstr_release(bstr) {sysfreestring(bstr);(bstr)=null;}  class ccoinitialize { public:     ccoinitialize() :         m_hr(coinitialize(null))     {}      ~ccoinitialize()     {         if(succeeded(m_hr)) {             qdebug() << "ccoinitialize: dtor";             couninitialize();         }     }      hresult m_hr; };  /**  worker class step through wmp com interface  , extact audio meta data contained within it,  */ class wmpmlcomhandler : public qobject { public:     wmpmlcomhandler(wmpmlimport* t) :         m_thread(t)     {         qdebug() << "wmpmlcomhandler::ctor" << qthread::currentthreadid();     }      ~wmpmlcomhandler()     {         qdebug() << "wmpmlcomhandler::dtor" << qthread::currentthreadid();     }      /**      method responsible walking through com interface , extracting      track , playlist metadata including artwork.      @returns return false if com api not parsed correctly.      */     bool parse()     {         bool b = true;          ccoinitialize ccoinit;          iwmpcore* piwmpcore = null;         iwmpcore3* piwmpcore3 = null;          iwmpplaylistcollection *pplaylistcollection;         iwmpplaylist *pmainlibplaylist;          clsid clsid;         clsid refid;         clsidfromstring(wmp_clsid, &clsid);         clsidfromstring(wmp_refiid, &refid);          if(succeeded(cocreateinstance(clsid, null, clsctx_all, refid, (void**)&piwmpcore)))         {             if(succeeded(piwmpcore->get_playlistcollection(&pplaylistcollection)))             {                 if(succeeded(piwmpcore->queryinterface(__uuidof(iwmpcore3), reinterpret_cast<void**>(&piwmpcore3))))                 {                     iwmpplaylistarray* pplaylistarray = null;                      if(succeeded(pplaylistcollection->getall(&pplaylistarray)))                     {                         long playlistcount = 0;                          if(succeeded(pplaylistarray->get_count(&playlistcount)))                         {                             iwmpplaylist* pplaylist = null;                              for(int playlistindex=0; playlistindex < playlistcount; playlistindex++)                             {                                 if (succeeded(pplaylistarray->item(playlistindex, &pplaylist)))                                 {                                     long lmediacount = 0;                                     if (succeeded(pplaylist->get_count(&lmediacount)))                                     {                                         fetchplaylist(pplaylist, null, playlistindex, lmediacount);                                     }                                     safe_release(pplaylist);                                 }                             }                         }                         safe_release(pplaylistarray);                     }                     safe_release(piwmpcore3);                 }                 safe_release(pplaylistcollection);             }             safe_release(piwmpcore);         }         safe_release(pmainlibplaylist);          return b;     }  private:      void fetchplaylist(iwmpplaylist* pplaylist, bstr bstrname, unsigned int playlistindex, long count)     {         //get playlist items         for(long mediaindex=0; mediaindex<count-1; mediaindex++)         {             iwmpmedia* pmediaitem = null;              if(succeeded(pplaylist->get_item(mediaindex, &pmediaitem)))             {                 iwmpmedia3 *pmedia3item = null;                  if (pmediaitem->queryinterface(__uuidof(iwmpmedia3), reinterpret_cast<void **>(&pmedia3item)) == s_ok)                 {                     long l = 0;                      qdebug() << "about call method for" << mediaindex << "time";                      if (pmedia3item && pmedia3item->getattributecountbytype(l"trackingid", 0, &l) == s_ok) //will crash here                     {                         qdebug() << "exited method for" << mediaindex << "time";                     }                 }                  safe_release(pmedia3item);                 safe_release(pmediaitem);            }         }         qdebug() << "*********complete*********";     }      wmpmlimport* m_thread; };  //==  wmpmlimport::wmpmlimport() :     m_comhandler(null) {     qdebug() << "wmpmlimporter ctor" << qthread::currentthreadid(); }  wmpmlimport::~wmpmlimport() { }  /**  reimplemented function runs function contents in new thread context.  parsing of com ran through thread. returning out of  thread end execution.  */ void wmpmlimport::run() {     qmutexlocker g(&m_lock);      m_comhandler = new wmpmlcomhandler(this);      g.unlock();     bool parseok = m_comhandler->parse();     g.relock();      delete m_comhandler;     m_comhandler = null; }