Problems finding memory leaks in MFC project

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4.33/5 (3 votes)

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I have an MFC SDI project that is quite big now. I need to check for memory leaks using Visual Studio. I have put in the code recommended in lots of articles I have read.

So, at the top of the source file that i want to check, I have added:

#define _CRTDBG_MAP_ALLOC
#include <stdlib.h>
#include <crtdbg.h>

as I want to get some info on the line that reports the leak that will allow me to find the point in the source code where he leak occurs I have put:

#ifdef _DEBUG
   #ifndef DBG_NEW
      #define DBG_NEW new ( _NORMAL_BLOCK , __FILE__ , __LINE__ )
      #define new DBG_NEW
   #endif
#endif">

now when I compile, at the linking stage I get:

myfile.obj LNK2005: "void __cdecl operator delet(void* ....etc.
already defined in uafxcwd.lib (afxmem.obj)
myapp.exe: fatal error LNK 1169: one or more multiply defined symbols defined.

Could somebody please tell me how to find memory leaks in an MFC project - it seems like there is a conflict bteween things that are already defined and what I am trying to add. I have read all that I can find but am no wiser yet (and am very frustrated :( ).

Posted 3-Aug-12 4:34am

Jackie Lloyd

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Sergey Alexandrovich Kryukov 3-Aug-12 14:01pm

How can you talk about a leak, if you still have a problem to link it? :-)
--SA

Jackie Lloyd 6-Aug-12 9:19am

I put some leaks in to test if they were being shown up - before I put in the code which wouldn't link.

Volynsky Alex 9-Aug-12 9:03am

A very useful question. +5!

1 solution

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Volynsky Alex · Accepted Answer · 2012-08-03T05:26:00

You can use something like :

C++

#include <string.h>
#include <malloc.h>
#include <crtdbg.h>

int main( )
{
        char *p1, *p2;
        int tmpDbgFlag;

        _CrtSetReportMode( _CRT_ERROR, _CRTDBG_MODE_FILE );
        _CrtSetReportFile( _CRT_ERROR, _CRTDBG_FILE_STDERR );
        /*
         * Set the debug-heap flag to keep freed blocks in the
         * heap's linked list - This will allow us to catch any
         * inadvertent use of freed memory
         */
        tmpDbgFlag = _CrtSetDbgFlag(_CRTDBG_REPORT_FLAG);
        tmpDbgFlag |= _CRTDBG_DELAY_FREE_MEM_DF;
        tmpDbgFlag |= _CRTDBG_LEAK_CHECK_DF;
        _CrtSetDbgFlag(tmpDbgFlag);
.....
}

In addition you will be helpful to review the following links:
http://msdn.microsoft.com/en-us/library/1y71x448%28v=vs.71%29.aspx[^]
http://mariusbancila.ro/blog/2010/07/12/how-to-find-the-source-of-memory-leaks/[^]
Memory Leak Detection[^]
http://msdn.microsoft.com/en-us/library/c99kz476%28v=vs.80%29.aspx[^]
http://msdn.microsoft.com/en-us/library/x98tx3cf%28v=vs.71%29.aspx[^]