ofstream and locales: how do they use heap memory?

Hi,

I have unit tests which I test for memory leaks. At the beginning and
at the end of a unit test I'm checking for the memory allocated on
heaps. If the number of bytes allocated on heaps differ, then a
memory leak is reported. However, an implementation of a standard
library can allocate or release memory on a heap during a test, which
will trigger a false alarm. One example of code that can cause a
false alarm is this one, which is reported to "leak" 96 bytes:

{
   std::ofstream("test");
}

I'm attaching below two programs that test this block. They are for
VC++ 2005.

PROGRAM 1 executes the block above, and checks for differences in
heaps. This is what it prints:

Difference of 96 bytes
Difference of 3 blocks

PROGRAM 2 also deals with this block, and it helped me with checking
the memory allocations and deallocations. I set the breakpoints in
the CustomAllocHook function and meticulously gathered the data shown
below as ALLOCATIONS AND RELEASES. It seems that heap allocations
have to do with locales.

Finally I'm getting to my question. Can I do something so that I
don't get these false reports on memory leaks? Like reinitializing
the part of the standard library that deals with locales?

Thanks & best,
Irek
www.irkos.org

********** PROGRAM 1 ***************************************

#include "stdafx.h"

#include <cassert>
#include <iostream>
#include <fstream>

#include <windows.h>
#include <crtdbg.h>

struct HeapInfo
{
     int bytes;
     int blocks;

     HeapInfo(): bytes(0), blocks(0)
     {
         HANDLE heaps[256];
         int noHeaps = GetProcessHeaps(256, heaps);

         HANDLE current_heap = GetProcessHeap();
         HANDLE crt_heap = (HANDLE) _get_heap_handle();

         for (int i = 0; i < noHeaps; ++i)
         {
             HANDLE heap = heaps[i];

             if (heap != crt_heap)
             {
                 BOOL locked = HeapLock(heap);
                 assert(locked);
                 BOOL valid = HeapValidate(heap, HEAP_NO_SERIALIZE,
NULL);
                 assert(valid);

                 PROCESS_HEAP_ENTRY entry;
                 entry.lpData = NULL;
                 while (HeapWalk(heap, &entry))
                 {
                     if (entry.wFlags & PROCESS_HEAP_ENTRY_BUSY)
                     {
                         bytes += entry.cbData;
                         ++blocks;
                     }
                 }

                 BOOL unlocked = HeapUnlock(heap);
                 assert(unlocked);
             }
         }
     }
};

int _tmain(int argc, _TCHAR* argv[])
{
     HeapInfo t1;

     {
         std::ofstream f("test.txt");
     }

     HeapInfo t2;

     std::cout << "Difference of " << t2.bytes - t1.bytes << " bytes
\n";
     std::cout << "Difference of " << t2.blocks - t1.blocks << "
blocks
\n";

     return 0;
}

********** PROGRAM 2 ***************************************

#include "stdafx.h"

#include <cassert>
#include <iostream>
#include <fstream>

#include <windows.h>
#include <crtdbg.h>

int count = 0;
int allocs = 0;
int reallocs = 0;
int frees = 0;

static int
CustomAllocHook(int nAllocType, void *userData, size_t size,
                 int nBlockType, long requestNumber,
                 const unsigned char *filename, int lineNumber)
{
     ++count;

     switch(nAllocType) {
         case _HOOK_ALLOC :
         ++allocs;
         break ;

         case _HOOK_REALLOC:
         ++reallocs;
         break ;

         case _HOOK_FREE :
         ++frees;
         break ;
     }

     return true;
}

int _tmain(int argc, _TCHAR* argv[])
{
     _CrtSetAllocHook(CustomAllocHook);
     {
         std::ofstream f("test.txt");
     }
     _CrtSetAllocHook(NULL);

     return 0;
}

********** ALLOCATIONS AND RELEASES ************************

action filename line address bytes
-----------------------------------------------------

new xiosbase 514 0x0037abf0 4
new xmutex.cpp 11 0x0037ac30 24
new streambuf 28 0x0037ac88 4
malloc mlock.c 279 0x0037acc8 24
malloc mlock.c 279 0x0037ad20 24
new xlocale 820 0x0037ad78 8
calloc setlocal.c 808 0x0037adc0 216
malloc setlocal.c 1133 0x003764f8 853
free setlocal.c 1168 0x003764f8 -853
free setlocal.c 214 0x00376028 -216
calloc setlocal.c 808 0x00376028 216
malloc setlocal.c 1133 0x003764f8 853
free setlocal.c 1168 0x003764f8 -853
free setlocal.c 214 0x0037adc0 -216
calloc setlocal.c 808 0x0037adc0 216
malloc setlocal.c 1133 0x003764f8 853
free setlocal.c 1168 0x003764f8 -853
free setlocal.c 214 0x00376028 -216
new locale0.cpp 177 0x00376028 8
delete streambuf 44 0x0037ac88 -4
delete xmutex.cpp 19 0x0037ac30 -24
delete ios.cpp 58 0x0037abf0 -4