Re: Why does MFC call _CrtDumpMemoryLeaks ?!?

"Martin T." <>
Mon, 14 Jul 2008 09:55:41 +0200
Doug Harrison [MVP] wrote:

On Fri, 11 Jul 2008 15:28:23 +0200, "Martin T." <> wrote:


It would be interesting to hear from someone who knows a rational behind
the MFC code or has some general thoughts how to get around it or to
hear why I'm completely mistaken :)

The rationale is that it was a mistake. (The real question is, "Why won't
they fix it?")

I think this actually is a relly big question, especially with the noise
Microsoft made with the "MFC Update Powered By BCGSoft" / "... the
Visual C++ team decided to reinvest in MFC ..."
Since people are working on it anyways, fix it fcs!
(Haven't tried it with VS 2008.)

For a workaround for those non-MFC DLLs you mentioned, see
if these threads help:

Though I never tried it, the second one should help with those DLLs you
can't modify.

Thank you, thank you, thank you :-)
I really can't think why that thread never turned up in my google
searches, esp. since I tried to solve this problem twice during the last
few months. (I guess I haven't google'd groups after I found the
_AFX_DEBUG_STATE code, though)
really solves the problem.
Might I add two points:
* On my Visual Studio 2005 I have to use a symbol from the DLL I create
to hold the MemoryLeakDetector object or otherwise the linker will not
load the DLL.
* I have added trace messages to to the ctor and dtor of the class:
_RPT0(_CRT_WARN, "== MemoryLeakDetector ==\n");

Allow me to re-post the code below and confirm that this is indeed
working with Visual Studio 2005.


#pragma once

#ifdef _DEBUG

#define IGNORE_MFC_LEAKS_API __declspec(dllexport)
#define IGNORE_MFC_LEAKS_API __declspec(dllimport)

IGNORE_MFC_LEAKS_API int use_ignore_mfc_leaks(void);

#endif // _DEBUG

[ CPP ]
// ignore_mfc_leaks.cpp : Defines the entry point for the DLL application.

#include "stdafx.h"
#include "ignore_mfc_leaks.h"
#include <crtdbg.h>
#include <string.h>

#ifdef _DEBUG

// Dummy function to make sure the DLL is loaded:
IGNORE_MFC_LEAKS_API int use_ignore_mfc_leaks(void)
    return 0;

static _CRT_REPORT_HOOK prevHook;
static bool SwallowReport;

class MemoryLeakDetector
    virtual ~MemoryLeakDetector();

int ReportingHook( int reportType, char* userMessage, int* retVal );


    //don't swallow assert and trace reports
    SwallowReport = false;
    //change the report function
    prevHook = _CrtSetReportHook(ReportingHook);

//this destructor is called after mfc has died
    //make sure that there is memory leak detection at the end of the program
    _CrtSetDbgFlag(_CrtSetDbgFlag(_CRTDBG_REPORT_FLAG) |

    //reset the report function to the old one
    _RPT0(_CRT_WARN, "=============== ~

static MemoryLeakDetector MLD; //this lives as long as this translation

int ReportingHook( int reportType, char* userMessage, int* retVal )
//_CrtDumpMemoryLeaks() outputs "Detected memory leaks!\n" and calls
//_CrtDumpAllObjectsSince(NULL) which outputs all leaked objects,
//ending this (possibly long) list with "Object dump complete.\n"
//In between those two headings I want to swallow the report.

    if ((strcmp(userMessage,"Detected memory leaks!\n") == 0) ||
SwallowReport) {
        if (strcmp(userMessage,"Object dump complete.\n") == 0)
            SwallowReport = false;
            SwallowReport = true;
        return true; //swallow it
        return false; //give it back to _CrtDbgReport()

#endif // _DEBUG

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