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Detecting a Memory Leak

Visual Studio 6.0

The following instructions and example show you how to detect a memory leak.

To detect a memory leak

  1. Create a CMemoryState object and call the Checkpoint member function to get the initial snapshot of memory.

  2. After you perform the memory allocation and deallocation operations, create another CMemoryState object and call Checkpoint for that object to get a current snapshot of memory usage.

  3. Create a third CMemoryState object, call the Difference member function, and supply the previous two CMemoryState objects as arguments. The return value for the Difference function will be nonzero if there is any difference between the two specified memory states, indicating that some memory blocks have not been deallocated.

    The following example shows how to check for memory leaks:

    // Declare the variables needed
    #ifdef _DEBUG
        CMemoryState oldMemState, newMemState, diffMemState;
        oldMemState.Checkpoint();
    #endif
    
        // do your memory allocations and deallocations...
        CString s = "This is a frame variable";
        // the next object is a heap object
        CPerson* p = new CPerson( "Smith", "Alan", "581-0215" );
    
    #ifdef _DEBUG
        newMemState.Checkpoint();
        if( diffMemState.Difference( oldMemState, newMemState ) )
        {
            TRACE( "Memory leaked!\n" );
        }
    #endif
    

    Notice that the memory-checking statements are bracketed by #ifdef _DEBUG / #endif blocks so that they are compiled only in Win32 Debug versions of your program.

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