Detailed memory leak dumps from a console app

Introduction

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

#ifndef IMWATCHINGYOULEAK
#define IMWATCHINGYOULEAK

#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__;
#endif

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.

Credits

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.

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