_CRTDBG_MAP_ALLOC
When the _CRTDBG_MAP_ALLOC flag is defined in the debug version of an application, the base version of the heap functions are directly mapped to their debug versions. The flag is used in Crtdbg.h to do the mapping. This flag is only available when the _DEBUG flag has been defined in the application.
For more information about using the debug version versus the base version of a heap function, see Using the Debug Version Versus the Base Version.