show location of biggest memory leak on Windows - windows

Question

My program has big leaks. I am using the debug heap by putting this in my stdafx.h:
#define _CRTDBG_MAP_ALLOC
#include <stdlib.h>
#include <crtdbg.h>
Then I'm capturing all the leaks in a text file by putting this code just before exit:
HANDLE hLogFile;
hLogFile = CreateFile( "T:\\MyProject\\heap.txt", GENERIC_WRITE,
FILE_SHARE_WRITE, NULL, CREATE_ALWAYS,
FILE_ATTRIBUTE_NORMAL, NULL);
_CrtSetReportMode(_CRT_WARN, _CRTDBG_MODE_FILE);
_CrtSetReportFile(_CRT_WARN, hLogFile);
_CrtDumpMemoryLeaks();
exit( EXIT_SUCCESS );
However even then the data is leak by leak, which is far too low-level information.

Answer 1

Stepping into _CrtDumpMemoryLeaks(), the code is actually easy to follow. I wrote my own function that summarizes the data, reporting bytes leaked for each line of code and sorting by leak size.
However it requires a static variable inside dbgheap.c in order to work. I've tried to make a version of dbgheap.c that doesn't have these as static symbols and tried to make a mini-DLL out of it (but it complains about a missing symbol I can't find anywhere in the MSFT code, _heap_regions). Instead what I've settled on is putting this code right before the code above calling _CrtDumpMemoryLeaks():
// Put a breakpoint here; step INTO the malloc, then in variable watch
// window evaluate: _CrtDumpMemoryLeakSummary( _pFirstBlock );
void* pvAccess = malloc(1);
And in turn this is the code for the _CrtDumpMemoryLeakSummary function:
#define _CRTBLD
#include "C:\Program Files\Microsoft Visual Studio 9.0\VC\crt\src\dbgint.h"
typedef struct {
const char* pszFileName;
int iLine;
int iTotal;
} Location_T;
#define MAX_SUMMARY 5000
static Location_T aloc[ MAX_SUMMARY ];
static int CompareFn( const void* pv1, const void* pv2 ) {
Location_T* ploc1 = (Location_T*) pv1;
Location_T* ploc2 = (Location_T*) pv2;
if ( ploc1->iTotal > ploc2->iTotal )
return -1;
if ( ploc1->iTotal < ploc2->iTotal )
return 1;
return 0;
}
void _CrtDumpMemoryLeakSummary( _CrtMemBlockHeader* pHead )
{
int iLocUsed = 0, iUnbucketed = 0, i;
for ( /*pHead = _pFirstBlock */;
pHead != NULL && /* pHead != _pLastBlock && */ iLocUsed < MAX_SUMMARY;
pHead = pHead->pBlockHeaderNext ) {
const char* pszFileName = pHead->szFileName ? pHead->szFileName : "<UNKNOWN>";
// Linear search is theoretically horribly slow but saves trouble of
// avoiding heap use while measuring heap use.
int i;
for ( i = 0; i < iLocUsed; i++ ) {
// To speed search, compare line number (fast) before strcmp() (slow).
// If szFileName were guaranteed to be __LINE__ then we could take advantage
// of __LINE__ always having the same address for any given file, and just
// compare pointers rather than using strcmp(). However, szFileName could
// be something else.
if ( pHead->nLine == aloc[i].iLine &&
strcmp( pszFileName, aloc[i].pszFileName ) == 0 ) {
aloc[i].iTotal += pHead->nDataSize;
break;
}
}
if ( i == iLocUsed ) {
aloc[i].pszFileName = pszFileName;
aloc[i].iLine = pHead->nLine;
aloc[i].iTotal = pHead->nDataSize;
iLocUsed++;
}
}
if ( iLocUsed == MAX_SUMMARY )
_RPT0( _CRT_WARN, "\n\n\nARNING: RAN OUT OF BUCKETS! DATA INCOMPLETE!!!\n\n\n" );
qsort( aloc, iLocUsed, sizeof( Location_T ), CompareFn );
_RPT0(_CRT_WARN, "SUMMARY OF LEAKS\n" );
_RPT0(_CRT_WARN, "\n" );
_RPT0(_CRT_WARN, "bytes leaked code location\n" );
_RPT0(_CRT_WARN, "------------ -------------\n" );
for ( i = 0; i < iLocUsed; i++ )
_RPT3(_CRT_WARN, "%12d %s:%d\n", aloc[i].iTotal, aloc[i].pszFileName, aloc[i].iLine );
}
It produces output like this:
SUMMARY OF LEAKS
bytes leaked code location
------------ -------------
912997 <UNKNOWN>:0
377800 ..\MyProject\foo.h:205
358400 ..\MyProject\A.cpp:959
333672 ..\MyProject\B.cpp:359
8192 f:\dd\vctools\crt_bld\self_x86\crt\src\_getbuf.c:58
6144 ..\MyProject\Interpreter.cpp:196
4608 ..\MyProject\Interpreter.cpp:254
3634 f:\dd\vctools\crt_bld\self_x86\crt\src\stdenvp.c:126
2960 ..\MyProject\C.cpp:947
2089 ..\MyProject\D.cpp:1031
2048 f:\dd\vctools\crt_bld\self_x86\crt\src\ioinit.c:136
2048 f:\dd\vctools\crt_bld\self_x86\crt\src\_file.c:133