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Deallocates or frees a memory block.

void free( 
   void *memblock 


Previously allocated memory block to be freed.

Return Value



The free function deallocates a memory block (memblock) that was previously allocated by a call to calloc, malloc, or realloc. The number of freed bytes is equivalent to the number of bytes requested when the block was allocated (or reallocated, in the case of realloc). If memblock is NULL, the pointer is ignored and free immediately returns. Attempting to free an invalid pointer (a pointer to a memory block that was not allocated by calloc, malloc, or realloc) may affect subsequent allocation requests and cause errors.

After a memory block has been freed, _heapmin minimizes the amount of free memory on the heap by coalescing the unused regions and releasing them back to the operating system. Freed memory that is not released to the operating system is restored to the free pool and is available for allocation again.

When the application is linked with a debug version of the C run-time libraries, free resolves to _free_dbg. For more information about how the heap is managed during the debugging process, see The CRT Debug Heap.


Function Required header Compatibility
free <stdlib.h> and <malloc.h> ANSI, Win 98, Win Me, Win NT, Win 2000, Win XP

For additional compatibility information, see Compatibility in the Introduction.


All versions of the C run-time libraries.


See the example for malloc.

See Also

Memory Allocation Routines | _alloca | calloc | malloc | realloc | _free_dbg | _heapmin | Run-Time Routines and .NET Framework Equivalents