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Verifies that a pointer is not null. In versions of the C run-time library before Visual Studio 2010, verifies that a specified memory range is valid for reading and writing (debug version only).

int _CrtIsValidPointer( 
   const void *address,
   unsigned int size,
   int access 


Points to the beginning of the memory range to test for validity.


Size of the specified memory range (in bytes).


Read/write accessibility to determine for the memory range.

_CrtIsValidPointer returns TRUE if the specified pointer is not null. In CRT library versions before Visual Studio 2010, returns TRUE if the memory range is valid for the specified operation or operations. Otherwise, the function returns FALSE.

Starting with the CRT library in Visual Studio 2010, the size and access parameters are ignored, and _CrtIsValidPointer only verifies that the specified address is not null. Because this test is easy to perform yourself, we do not recommend you use this function. In versions before Visual Studio 2010, the function verifies that the memory range beginning at address and extending for size bytes is valid for the specified accessibility operation or operations. When access is set to TRUE, the memory range is verified for both reading and writing. When access is FALSE, the memory range is only validated for reading. When _DEBUG is not defined, calls to _CrtIsValidPointer are removed during preprocessing.

Because this function returns TRUE or FALSE, it can be passed to one of the _ASSERT macros to create a simple debugging error handling mechanism. The following example causes an assertion failure if the memory range is not valid for both reading and writing operations:

_ASSERTE( _CrtIsValidPointer( address, size, TRUE ) );

For more information about how _CrtIsValidPointer can be used with other debug functions and macros, see Macros for Reporting. For information about how memory blocks are allocated, initialized, and managed in the debug version of the base heap, see CRT Debug Heap Details.


Required header



_CrtIsValidPointer is a Microsoft extension. For compatibility information, see Compatibility.


Debug versions of C run-time libraries only.

See the example for the _CrtIsValidHeapPointer topic.

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

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