_CrtIsValidHeapPointer

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

int _CrtIsValidHeapPointer( const void *userData );

For additional compatibility information, see Compatibility in the Introduction.

Libraries

Return Value

_CrtIsValidHeapPointer returns TRUE if the specified pointer is in the local heap; otherwise, the function returns FALSE.

Parameter

userData

Pointer to the beginning of an allocated memory block

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 dynamically linked library (DLL) contains a static link to the run-time library, then 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 will cause 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.

Example

/*
 * 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

void 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.

Debug Functions