_CrtIsValidHeapPointer

Article
06/05/2017

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The latest version of this topic can be found at _CrtIsValidHeapPointer.

Verifies that a specified pointer is in a heap allocated by some C run-time library, but not necessarily by the caller's CRT library. In versions of the CRT before Visual Studio 2010, this verifies that the specified pointer is in the local heap (debug version only).

Syntax

  
      int _CrtIsValidHeapPointer(   
   const void *userData   
);

Parameters

userData
Pointer to the beginning of an allocated memory block.

Return Value

_CrtIsValidHeapPointer returns TRUE if the specified pointer is in the heap shared by all CRT library instances. In versions of the CRT before Visual Studio 2010, this returns TRUE if the specified pointer is in the local heap. Otherwise, the function returns FALSE.

Remarks

We do not recommend that you use this function. Starting with the Visual Studio 2010 CRT library, all CRT libraries share one OS heap, the process heap. The _CrtIsValidHeapPointer function reports whether the pointer was allocated in a CRT heap, but not that it was allocated by the caller's CRT library. For example, consider a block allocated by using the Visual Studio 2010 version of the CRT library. If the _CrtIsValidHeapPointer function exported by the Visual Studio 2012 version of the CRT library tests the pointer, it returns TRUE. This is no longer a useful test. In versions of the CRT library before Visual Studio 2010, the function is used to ensure that a specific memory address is within the local heap. The local heap refers to the heap created and managed by a particular instance of the C run-time library. If a dynamic-link library (DLL) contains a static link to the run-time library, it has its own instance of the run-time heap, and therefore its own heap, independent of the application's local heap. When _DEBUG is not defined, calls to _CrtIsValidHeapPointer 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 specified address is not located within the local heap:

_ASSERTE( _CrtIsValidHeapPointer( userData ) );

For more information about how _CrtIsValidHeapPointer 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.

Requirements

Routine	Required header
`_CrtIsValidHeapPointer`	<crtdbg.h>

For more compatibility information, see Compatibility in the Introduction.

Libraries

Debug versions of C run-time libraries only.

Example

The following example demonstrates how to test whether memory is valid when it is used with C run-time libraries before Visual Studio 2010. This example is provided for users of legacy CRT library code.

// crt_isvalid.c  
/*  
 * This program allocates a block of memory using _malloc_dbg  
 * and then tests the validity of this memory by calling   
 * _CrtIsMemoryBlock,_CrtIsValidPointer, and _CrtIsValidHeapPointer.  
 */  
  
#include <stdio.h>  
#include <string.h>  
#include <malloc.h>  
#include <crtdbg.h>  
  
#define  TRUE   1  
#define  FALSE  0  
  
int main( void )  
{  
        char *my_pointer;  
  
        /*   
         * Call _malloc_dbg to include the filename and line number  
         * of our allocation request in the header information  
         */  
        my_pointer = (char *)_malloc_dbg( sizeof(char) * 10,   
        _NORMAL_BLOCK, __FILE__, __LINE__ );  
  
        // Ensure that the memory got allocated correctly  
        _CrtIsMemoryBlock((const void *)my_pointer, sizeof(char) * 10,   
        NULL, NULL, NULL );  
  
         // Test for read/write accessibility  
        if (_CrtIsValidPointer((const void *)my_pointer,   
        sizeof(char) * 10, TRUE))  
                printf("my_pointer has read and write accessibility.\n");  
        else  
                printf("my_pointer only has read access.\n");  
  
        // Make sure my_pointer is within the local heap  
        if (_CrtIsValidHeapPointer((const void *)my_pointer))  
                printf("my_pointer is within the local heap.\n");  
        else  
                printf("my_pointer is not located within the local"  
                       " heap.\n");  
  
        free(my_pointer);  
}

Output

my_pointer has read and write accessibility.  
my_pointer is within the local heap.

.NET Framework Equivalent

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

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