heapchecknode

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Header File

alloc.h

Prototype

int heapchecknode(void *node);

Description

Checks and verifies a single node on the heap.

If a node has been freed and heapchecknode is called with a pointer to the freed block, heapchecknode can return _BADNODE rather than the expected _FREEENTRY. This is because adjacent free blocks on the heap are merged, and the block in question no longer exists.

Return Value

One of the following values:

_BADNODE	Node could not be found
_FREEENTRY	Node is a free block
_HEAPCORRUPT	Heap has been corrupted
_HEAPEMPTY	No heap
_USEDENTRY	Node is a used block

Portability

	POSIX	ANSI C	ANSI C++	Win32	Win64	macOS
heapchecknode				+

Example

#include <stdio.h>
#include <alloc.h>
#define NUM_PTRS  10
#define NUM_BYTES 16

int main(void) {
    char *array[NUM_PTRS];
    int i;
    for (i = 0; i < NUM_PTRS; i++)
        array[i] = (char *) malloc(NUM_BYTES);
    for (i = 0; i < NUM_PTRS; i += 2)
        free(array[i]);
    for (i = 0; i < NUM_PTRS; i++) {
        printf("Node %2d ", i);
        switch (heapchecknode(array[i])) {
        case _HEAPEMPTY:
            printf("No heap.\n");
            break;
        case _HEAPCORRUPT:
            printf("Heap corrupt.\n");
            break;
        case _BADNODE:
            printf("Bad node.\n");
            break;
        case _FREEENTRY:
            printf("Free entry.\n");
            break;
        case _USEDENTRY:
            printf("Used entry.\n");
            break;
        default:
            printf("Unknown return code.\n");
            break;
        }
    }
    return 0;
}