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memory debug in mfc

Posted on 2000-05-09
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Last Modified: 2013-11-20
Is there a way to alter the memory debug behavior of mfc?

Mfc checks for memory leaks *before* the program exits (thus reporting
memory leaks on globals).  This generates a lot of messages in my
application (and I get annoyed by them). (for instance, try this:
#include <iostream> #include <crtdbg.h> void main () {
_CrtDumpMemoryLeaks() }; ,this'll generate false memory leak messages
and this is exactly what mfc does).

Normally you can do something like :

_CrtSetDbgFlag(_CrtSetDbgFlag(_CRTDBG_REPORT_FLAG)
      | _CRTDBG_LEAK_CHECK_DF | _CRTDBG_ALLOC_MEM_DF
      | _CRTDBG_CHECK_ALWAYS_DF);

,but I guess mfc resets those flag bits.

So, can anyone advise me on this one?
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Question by:podb
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6 Comments
 
LVL 86

Expert Comment

by:jkr
ID: 2792309
There are actually two things that can be done to prevent this:

- turn off the debugging flags

// Get the current state of the flag
// and store it in a temporary variable
int tmpFlag = _CrtSetDbgFlag( _CRTDBG_REPORT_FLAG );

tmpFlag &= ~_CRTDBG_CHECK_ALWAYS_DF;
tmpFlag &= ~_CRTDBG_LEAK_CHECK_DF ;
tmpFlag &= ~_CRTDBG_ALLOC_MEM_DF ;

// Set the new state for the flag
_CrtSetDbgFlag( tmpFlag );

- 'swallow' the messages:

int     _CRTAPI1    __MygReportHook (   int     nType,  
                                        char    *pszMsg,
                                        int     *pnRetVal
                                    )
{

    return( TRUE);
}

_CrtSetReportHook   (   ( _CRT_REPORT_HOOK) __MyReportHook);



0
 

Author Comment

by:podb
ID: 2792381
I don't want to prevent memory debug, I only want to do it at program exit. Normally you do that by setting the _CRTDBG_ALLOC_MEM_DF flag.
I have tried to add this (see *) to my application constructor (is this the correct place to add this?), but it didn't help (that's why I thought mfc is calling _CrtSetDbgFlag itself).

(*)
_CrtSetDbgFlag(_CrtSetDbgFlag(_CRTDBG_REPORT_FLAG)
      | _CRTDBG_LEAK_CHECK_DF | _CRTDBG_ALLOC_MEM_DF
      | _CRTDBG_CHECK_ALWAYS_DF);

So, the question is: how do I tell mfc to only do a memory leak test at program exit?

By the way, jkr, thanks for taking the time.
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LVL 3

Expert Comment

by:MDarling
ID: 2792634
There's a flag called afxMemDF which you can use.  Not sure you can only check at exit though.

regards,
Mike.
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Author Comment

by:podb
ID: 2792646
No, you cannot.
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LVL 86

Accepted Solution

by:
jkr earned 600 total points
ID: 2792753
Well, after swiching off the debug logging (as I erroneously suggested before), you could always call

_CrtDumpMemoryLeaks ();

before your program exits.

OR:

(at startup)

_CrtMemState state ;

_CrtMemCheckpoint( &state );

(at shutdown)

_CrtMemDumpAllObjectsSince( &state );
0
 

Author Comment

by:podb
ID: 2792857
I see no good reason to call _CrtDumpMemoryLeaks().  This will always be called *before* globals, etc. are destroyed.  Setting the flag _CRTDBG_ALLOC_MEM_DF, however gives the right behavior.

I have done some tracking myself and in ...\mfc\src\dumpinit.cpp, line 131, in the destructor of _AFX_DEBUG_STATE you'll see the call to _CrtDumpMemoryLeaks(), which is called through CProcessLocal<_AFX_DEBUG_STATE>::~CProcessLocal<_AFX_DEBUG_STATE>() (This is called when there are still 8 calls on the call stack).

But hey, you can have the 200 points.  I'm starting to belief there is no good solution.
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