FREE() Crashing

Posted by Vishuonline on December 15, 2005, 7:04 pm

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Hi Folks,

I am facing a problem with CRT function call free() to dellocate memory I am
allocating by calloc call. My device is Orange SPV e200 Smartphone.
My free() call successfully deallocates the memory intermittently. i mean if
I run the application.. say 3 times. It deallocates 2 times.. at times.. only
1... And .. it gets better.. when it DOES NOT execute successfully.. its
CRASHES the APP.
I always check the pointer to be NOT NULL, before sending it to free() call.
Like
if(myPtr != NULL){free(myPtr);myPtr = NULL;}

I dont know how to address this issue. I am not able to do any on-device
debugging with this device,, for some strange reason. Whenever I launch the
app for on-device debugging.... the break point is never reached and the IDE
dies on me. Ok.. on-device debuggign.. problem apart.. I need some help on
the APP-CRASH on free() call.

Best,

Posted by Alex Feinman (MVP) on December 16, 2005, 2:51 am

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Vishuonline wrote:
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Check that the pointer you pass to free() is the same you got from
calloc(), i.e. it did not get overwritten

Posted by Vishuonline on December 16, 2005, 11:39 am

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Yes. I checked that one too.. All the pointers are unique place holders. And
there are on threads in the picture. Infact. I even check and display the
content inside the buffer, before calling free(),, it Still crashes... Any
clues??
Example code:
//////////////////////////////////////////////////////////
char * fName = (char *)calloc(strlen(colonTOKEN)-2,sizeof(char));
strcpy(fName,colonTOKEN+2);
TCHAR * fNameBuffer = (TCHAR *)calloc(strlen(fName),sizeof(TCHAR));
wsprintf(fNameBuffer,_T("%S"),fName);
TimedMessageBox(hwnd,fNameBuffer,_T("FULLNAME Debug Message"),MB_OK,1500);
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TimedMessageBox(hwnd,_T("ADDED"),_T("APPLICATION DEBUG"),MB_OK,1500);
//IT NEVER DISPLAYS THE "GOING TO NEXTTOKEN" MESSAGE BOX
if(fName != NULL && strlen(fName))
{
free(fName);//IT CRASHES HERE
fName = NULL;
}
if(fNameBuffer != NULL && wcslen(fNameBuffer))
{
free(fNameBuffer);
fNameBuffer = NULL;
}

TimedMessageBox(hwnd,_T("GOING TO NEXTTOKEN"),_T("APPLICATION
DEBUG"),MB_OK,1500);
//////////////////////////////////////////////////////////

Vishu

"Alex Feinman (MVP)" wrote:

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Posted by Vishuonline on December 16, 2005, 12:44 pm

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Hmm.. I think I might have solved the issue.. I think the order of free()
calls is playing spoil sport.. This issue is related to fragmentation support
in heap memory..
I read that.. smartphone DOES support fragmentation.. which.. i believe
should allow free() calls.. irrespective of the order or calloc/malloc calls.
I dont know.. why the current behavior occurs.... but.. atleast.. its works
fine.. if i set the order right..

Thanks!

"Alex Feinman (MVP)" wrote:

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Posted by Michael J. Salamone on December 17, 2005, 10:07 am

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The error is not in the CRT or fragmentation or order of frees.

The error is a heap corruption, calling free multiple times on the same
pointer, or some other bug which is putting the heap in a corrupt or
inconsistent state. The corruption occured *before* the call to free that
tanks.

You might sprinkle some calls to HeapValidate in your code to help narrow
down where the problem is.

If you want a tool that *might* help, check the link below.

--
Michael Salamone [eMVP]
Entrek Software, Inc.
www.entrek.com

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