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Posted 21 May 2002

Detailed memory leak dumps from a console app

, 21 May 2002
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How to get path and line number info for memory leaks, in a console app


Finding memory leaks in a non-MFC app can be difficult because the debugger doesn't display path and line number info in the debug window. But, it's quite easy to enable that info. Here's how:

Step 1

Copy this to a file called LeakWatcher.h


#include <crtdbg.h>

#ifdef _DEBUG
void* operator new(size_t nSize, const char * lpszFileName, int nLine)
    return ::operator new(nSize, 1, lpszFileName, nLine);
#define DEBUG_NEW new(THIS_FILE, __LINE__)

#define MALLOC_DBG(x) _malloc_dbg(x, 1, THIS_FILE, __LINE__);
#define malloc(x) MALLOC_DBG(x)

#endif // _DEBUG

#endif // #include guard

Step 2

Call _CrtDumpMemoryLeaks(); at the end of your program (or wherever you want to see outstanding memory allocations).

Steps 3...N

Add this to each of your source files (after your last #include) :

#include "LeakWatcher.h"

#ifdef _DEBUG
#define new DEBUG_NEW
#undef THIS_FILE
static char THIS_FILE[] = __FILE__;

What does it do?

This does the same thing an MFC app does - it provides the path and line number of each allocation to the C-runtime allocation routines. Those routines store the path and line number for each allocation, and spit them out when you call _CrtDumpMemoryLeaks();. You should recognize that little chunk of code in step 3 from every source file that the AppWizard (and ClassWizard, mostly) has ever created.

Why not just use _CRTDBG_MAP_ALLOC?

#define _CRTDBG_MAP_ALLOC will provide file/line info for leaks caused by malloc, but for leaks with new, it ends up telling you that the leak occurred in crtdbg.h (because that's where MS defined their new) - not really useful.


This represents about ten minutes of searching through Microsoft's C runtime and MFC source files. So, all of the credit goes to MS. But, all of the blame goes to MS, too, for not making this part of the non-MFC headers. Anyway, have fun and be excellent to each other.


This article has no explicit license attached to it but may contain usage terms in the article text or the download files themselves. If in doubt please contact the author via the discussion board below.

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About the Author

Chris Losinger
Software Developer
United States United States
Chris Losinger is the president of Smaller Animals Software, Inc..

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Comments and Discussions

GeneralTwo Problems Pin
Andrew @ Neoteck4-May-05 21:36
sussAndrew @ Neoteck4-May-05 21:36 
Hi all,

I'll preface this by saying I tried out this code on a small application to test it out and it works a treat!

However, I've tried using it into a large program written by someone else, who has asked me to maintain the code, and I get a lot of compiler errors and warnings.

<br />
warning C4291: 'void *__cdecl operator new(unsigned int,const char *,int)' : no matching operator delete found; memory will not be freed if initialization throws an exception<br />

Appears for every single time the new operator is called (which is a lot of times!).

Secondly, I get errors appearing like this one:

<br />
c:\program files\microsoft visual studio\vc98\include\fstream(217) : error C2059: syntax error : '&'<br />
        c:\program files\microsoft visual studio\vc98\include\fstream(213) : while compiling class-template member function 'void __thiscall std::basic_filebuf<char,struct std::char_traits<char> >::_Init(struct _iobuf *,enum std::basic_filebuf<char,<br />

The line in question in fstream is
new (&_Loc) locale;
which clearly says it must be something wrong with my overloaded new operator.

Every CPP file in this program only uses the one header file, although that header file does call several other header files as well. I've included the
<br />
<br />
#ifdef _DEBUG<br />
#define new DEBUG_NEW<br />
#undef THIS_FILE<br />
static char THIS_FILE[] = __FILE__;<br />
#endif<br />

at the very bottom of the main header file.

I don't need to be told how bad a practice it is of having ALL the source read out of the same header file. I'm just maintaining this code, I didn't write it.

Please help. Finding the source of the memory leaks without this is going to be damn near impossible.
GeneralRe: Two Problems Pin
Andrew @ Neoteck4-May-05 21:37
sussAndrew @ Neoteck4-May-05 21:37 
GeneralRe: Two Problems Pin
Chris Losinger5-May-05 0:59
memberChris Losinger5-May-05 0:59 
GeneralRe: Two Problems Pin
Andrew @ Neoteck5-May-05 13:34
sussAndrew @ Neoteck5-May-05 13:34 
GeneralRe: Two Problems Pin
Nosferatus22-Jul-05 5:53
memberNosferatus22-Jul-05 5:53 
GeneralRe: Two Problems Pin
Bob Stanneveld1-Feb-06 21:15
memberBob Stanneveld1-Feb-06 21:15 

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