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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_dbg | Microsoft Docs
11/04/2016
cpp-standard-libraries
article
_free_dbg
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DLLExport
_free_dbg
free_dbg
C++
memory blocks, deallocating
freeing memory
_free_dbg function
free_dbg function
fc5e8299-616d-48a0-b979-e037117278c6
16
corob-msft
corob
ghogen

_free_dbg

Frees a block of memory in the heap (debug version only).

Syntax

void _free_dbg(   
   void *userData,  
   int blockType   
);

Parameters

userData
Pointer to the allocated memory block to be freed.

blockType
Type of allocated memory block to be freed: _CLIENT_BLOCK, _NORMAL_BLOCK, or _IGNORE_BLOCK.

Remarks

The _free_dbg function is a debug version of the free function. When _DEBUG is not defined, each call to _free_dbg is reduced to a call to free. Both free and _free_dbg free a memory block in the base heap, but _free_dbg accommodates two debugging features: the ability to keep freed blocks in the heap's linked list to simulate low memory conditions and a block type parameter to free specific allocation types.

_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.

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 CRT Debug Heap Details. 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 Debug Versions of Heap Allocation Functions.

Requirements

Routine Required header
_free_dbg <crtdbg.h>

For more compatibility information, see Compatibility in the Introduction.

Example

For a sample of how to use _free_dbg, see crt_dbg2.

See Also

Debug Routines
_malloc_dbg