How to: Take Memory Snapshots

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This topic shows how to take snapshots of memory to help locate a memory leak.

To detect a memory leak

1. Create a CMemoryState Members object and call the CMemoryState::Checkpoint member function. This creates the first memory snapshot.

2. After your program performs its memory allocation and deallocation operations, create another CMemoryState object and call Checkpoint for that object. This gets a second snapshot of memory usage.

3. Create a third CMemoryState object and call its CMemoryState::Difference member function, supplying as arguments the two previous CMemoryState objects. If there is a difference between the two memory states, the Difference function returns a nonzero value. This indicates that some memory blocks have not been deallocated.

   This example shows what the code looks like:

   // 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.

   Now that you know a memory leak exists, you can use another member function, CMemoryState::DumpStatistics, to Memory Statistic Viewing that will help you locate it.

See Also

Reference

_DEBUG

Other Resources

Memory Leak Detection in MFC