CMemoryState

This is a discussion on CMemoryState within the Windows Programming forums, part of the Platform Specific Boards category; After about 16 hours of trying to figure out something I've come to reach a hypothesis... When using CMemoryState (and ...

  1. #1
    Magically delicious LuckY's Avatar
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    CMemoryState

    After about 16 hours of trying to figure out something I've come to reach a hypothesis...
    When using CMemoryState (and its Checkpoint() and Difference()) functions, it effs up when you have a vector contained in it. Check out the following code:
    Code:
      CMemoryState oldMemState, newMemState, diffMemState;
      oldMemState.Checkpoint();
      std::vector<TCHAR*> vect;
      newMemState.Checkpoint();
      _ASSERTE (diffMemState.Difference( oldMemState, newMemState ) == FALSE);
    The assertion is thrown in this case.. I was trying for many hours and I'm just ........ed for wasting my time thinking I had a leak in my code... Perhaps I am wrong, but I don't see how I could be with the simple, straight-forward code above.

    This is just something to keep in mind if you ever try using CMemoryState to catch a memory leak.

  2. #2
    Registered User Codeplug's Avatar
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    vect may free any memory from the heap when it goes out of scope (ie the destructor is called). Try this:
    Code:
    CMemoryState oldMemState, newMemState, diffMemState;
    oldMemState.Checkpoint();
    {
       std::vector<TCHAR*> vect;
    }
    newMemState.Checkpoint();
    _ASSERTE (diffMemState.Difference( oldMemState, newMemState ) == FALSE);
    gg

  3. #3
    Registered User Codeplug's Avatar
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    I just ran the code (as you originally posted it) in an MFC dialog app using VC++ 6.0 (and all the patches). I did not get the assert.

    Do you have other threads running? CMemoryState is not thread specific since multiple threads can share the same heap.

    gg

  4. #4
    Magically delicious LuckY's Avatar
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    My app has only a single thread.
    Believe me, I tried and tried everything you could think of for a day and a half to figure out what was causing the assertion. The reason I was doing so in the first place is because I modified my class to use only dynamically alloc'd c-strings.. Eventually, I made everything static again and was still getting the Difference().

    I finally figured that perhaps the vector was causing it since it is the only thing in my class that was allocating any heap. Here are a few things I tried (btw I was doing this from my CMainFrame::OnCreate()):
    in my class I have a vect as a private member, so I did this:
    Code:
    //old checkpoint
      Settings *s = new Settings;
      delete [] s;
    //new checkpoint
    
    or
    
    //old checkpoint
    {
      Settings s;
    }
    //new checkpoint
    Aside from all that, I just ran it again and didn't get the assertion!!! I really am not crazy, but merely in the Twilight Zone it would seem.. I tested and tested and tested it. I even tested it more after posting this thread and I kept getting the assertion! But I just ran it again and it was fine!

    Sometimes I just want to kill myself (not literally, you understand).

    Thanks for the response CodePlug... If I ever figure it out it won't be soon enough.

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