_CrtIsValidHeapPointer

Article
07/22/2011

Verifies that a specified pointer is in the local heap (debug version only).

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 local heap. Otherwise, the function returns FALSE.

Remarks

The _CrtIsValidHeapPointer 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 Using Macros for Verification and Reporting. For information about how memory blocks are allocated, initialized, and managed in the debug version of the base heap, see Memory Management and the Debug Heap.

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

// 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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