I'm doing a conversion of my system from borland v4.53 to msvc. While
testing, using the debug version of the system as generated by msvc, I'm
receiving an assert error in free() (actually _free_dbg_lk()). A code snipet
from _free_dbg_lk() in dbgheap.c, where the assert is happening follows:
...
/* optionally reclaim memory */
if (!(_crtDbgFlag & _CRTDBG_DELAY_FREE_MEM_DF))
{
    /* remove from the linked list */
    if (pHead->pBlockHeaderNext)
    {
        pHead->pBlockHeaderNext->pBlockHeaderPrev =
pHead->pBlockHeaderPrev;
    }
    else
    {
        _ASSERTE(_pLastBlock == pHead);
        _pLastBlock = pHead->pBlockHeaderPrev;
    }
    if (pHead->pBlockHeaderPrev)
    {
        pHead->pBlockHeaderPrev->pBlockHeaderNext =
pHead->pBlockHeaderNext;
    }
    else
    {
==> assert fails here
==>        _ASSERTE(_pFirstBlock == pHead);
        _pFirstBlock = pHead->pBlockHeaderNext;
    }
...

What I'm trying to do is free memory allocated to a struct that contained
structs whose memory has already been freed (successfully).
pHead->pBlockHeaderPrev is NULL and it should be.

When the space is calloc'd, _pFirstBlock's address wasn't the same as pHead
(32 byte difference). Why should it be the same now?

I don't know if this is something I should worry about. If anyone has any
ideas on how to go about fixing this or things to look at while debugging,

thanks.

--

I've seen this happen under a couple of circumstances: 1) errors in my
program that were clobbering the heap and 2) mismatched heap functions (some
modules built with DLL version others with static or some modules built
debug and others not).

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