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Frees a block of memory that was allocated with _aligned_malloc or _aligned_offset_malloc (debug only).

void _aligned_free_dbg(
   void *memblock


A pointer to the memory block that was returned to the _aligned_malloc or _aligned_offset_malloc function.

The _aligned_free_dbg function is a debug version of the _aligned_free function. When _DEBUG is not defined, each call to _aligned_free_dbg is reduced to a call to _aligned_free. Both _aligned_free and _aligned_free_dbg free a memory block in the base heap, but _aligned_free_dbg accommodates a debugging feature: the ability to keep freed blocks in the heap's linked list to simulate low memory conditions.

_aligned_free_dbg performs a validity check on all specified files and block locations before performing the free operation. The application is not expected to provide this information. When a memory block is freed, the debug heap manager automatically checks the integrity of the buffers on either side of the user portion and issues an error report if overwriting has occurred. If the _CRTDBG_DELAY_FREE_MEM_DF bit field of the _crtDbgFlag flag is set, the freed block is filled with the value 0xDD, assigned the _FREE_BLOCK block type, and kept in the heap's linked list of memory blocks.

In Visual C++ 2005, if an error occurs in freeing the memory, errno is set with information from the operating system on the nature of the failure. For more information, see errno, _doserrno, _sys_errlist, and _sys_nerr.

For information about how memory blocks are allocated, initialized, and managed in the debug version of the base heap, see Memory Management and the Debug Heap. For information about the allocation block types and how they are used, see Types of Blocks on the Debug Heap. For information about the differences between calling a standard heap function and its debug version in a debug build of an application, see Using the Debug Version Versus the Base Version.


Required header



For more compatibility information, see Compatibility in the Introduction.

Not applicable. To call the standard C function, use PInvoke. For more information, see Platform Invoke Examples.