free.md

title	ms.custom	ms.date	ms.reviewer	ms.suite	ms.technology	ms.tgt_pltfrm	ms.topic	apiname	apilocation	apitype	f1_keywords	dev_langs	helpviewer_keywords	ms.assetid	caps.latest.revision	author	ms.author	manager
free | Microsoft Docs		11/04/2016			cpp-standard-libraries		article	free	msvcrt.dll msvcr80.dll msvcr90.dll msvcr100.dll msvcr100_clr0400.dll msvcr110.dll msvcr110_clr0400.dll msvcr120.dll msvcr120_clr0400.dll ucrtbase.dll api-ms-win-crt-heap-l1-1-0.dll	DLLExport	free	C++	memory blocks, deallocating free function	74ded9cf-1863-432e-9306-327a42080bb8	14	corob-msft	corob	ghogen

free

Deallocates or frees a memory block.

Syntax

void free(   
   void *memblock   
);  

Parameters

memblock
Previously allocated memory block to be freed.

Remarks

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.

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.

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.

free is marked __declspec(noalias), meaning that the function is guaranteed not to modify global variables. For more information, see noalias.

To free memory allocated with _malloca, use _freea.

Requirements

Function	Required header
free	<stdlib.h> and <malloc.h>

For additional compatibility information, see Compatibility in the Introduction.

Example

See the example for malloc.

See Also

Memory Allocation
_alloca
calloc
malloc
realloc
_free_dbg
_heapmin
_freea