Question

How can I detect memory leaks in QtCreator on Windows? On the doc, they recommend Memcheck but it only works on Mac and Linux. Any suggestion for Windows?

Answer 1

After many tries I finally found a method to detect the memory leaks of a Qt project on Windows:

1) First, it cannot be done directly in Qt Creator so you need to create a Visual C++ project to do the memory leak detection. Thankfully, qmake makes this easy. Open the Qt SDK command line tool and run:

qmake -spec win32-msvc2008 -tp vc

This will convert your project to a .vcproj.

2) Open this project and add the necessary code for memory leak detection:

To your main.cpp file:

// Necessary includes and defines for memory leak detection:
#ifdef _MSC_VER
#define _CRTDBG_MAP_ALLOC
#include <crtdbg.h>
#endif // _MSC_VER


#if defined(_MSC_VER)

// Code to display the memory leak report
// We use a custom report hook to filter out Qt's own memory leaks
// Credit to Andreas Schmidts - http://www.schmidt-web-berlin.de/winfig/blog/?p=154

_CRT_REPORT_HOOK prevHook;

int customReportHook(int /* reportType */, char* message, int* /* returnValue */) {
  // This function is called several times for each memory leak.
  // Each time a part of the error message is supplied.
  // This holds number of subsequent detail messages after
  // a leak was reported
  const int numFollowupDebugMsgParts = 2;
  static bool ignoreMessage = false;
  static int debugMsgPartsCount = 0;

  // check if the memory leak reporting starts
  if ((strncmp(message,"Detected memory leaks!\n", 10) == 0)
    || ignoreMessage)
  {
    // check if the memory leak reporting ends
    if (strncmp(message,"Object dump complete.\n", 10) == 0)
    {
      _CrtSetReportHook(prevHook);
      ignoreMessage = false;
    } else
      ignoreMessage = true;

    // something from our own code?
    if(strstr(message, ".cpp") == NULL)
    {
      if(debugMsgPartsCount++ < numFollowupDebugMsgParts)
        // give it back to _CrtDbgReport() to be printed to the console
        return FALSE;
      else
        return TRUE;  // ignore it
    } else
    {
      debugMsgPartsCount = 0;
      // give it back to _CrtDbgReport() to be printed to the console
      return FALSE;
    }
  } else
    // give it back to _CrtDbgReport() to be printed to the console
    return FALSE;
}

#endif



int main(int argc, char *argv[]) {
    #if defined(_MSC_VER)
    _CrtSetDbgFlag(_CRTDBG_ALLOC_MEM_DF | _CRTDBG_LEAK_CHECK_DF);
    prevHook = _CrtSetReportHook(customReportHook);
    // _CrtSetBreakAlloc(157); // Use this line to break at the nth memory allocation
    #endif

    QApplication* app = new QApplication(argc, argv);   
    int appError = app->exec();
    delete app;

    #if defined(_MSC_VER)
    // Once the app has finished running and has been deleted,
    // we run this command to view the memory leaks:
    _CrtDumpMemoryLeaks();
    #endif 

    return appError;
}

3) With this, your project should now be able to detect memory leaks. Note the _MSC_VER defines so that this code is only executed when your run it from Visual C++ (not from Qt Creator). It means you can still do the development with Qt Creator and just re-run step 1 whenever you need to check for memory leaks.

4) To break at a particular memory allocation, use _CrtSetBreakAlloc() More information memory leak detection on Microsoft’s website: http://msdn.microsoft.com/en-us/library/e5ewb1h3%28v=vs.80%29.aspx