_debug_calloc - Allocate and Initialize Memory

Format

#include <stdlib.h>   /* also in <malloc.h> */
void *_debug_calloc(size_t num, size_t size,
                    const char *file, size_t line);

Language Level: Extension

_debug_calloc is the debug version of calloc. Like calloc, it allocates memory from the default heap for an array of num elements, each of length size bytes. It then initializes all bits of each element to 0.

In addition, _debug_calloc makes an implicit call to _heap_check, and stores the name of the file file and the line number line where the storage is allocated. This information can be used later by the _heap_check, _dump_allocated or _dump_allocated_delta functions.

To use _debug_calloc, you must compile with the debug memory -qheapdebug compiler option. This option maps all calloc calls to _debug_calloc.

Note: The -qheapdebug option maps all calls to memory management functions (including heap-specific versions) to their debug counterparts. To prevent a call from being mapped, parenthesize the function name.

To reallocate or free memory allocated by _debug_calloc, use _debug_realloc and _debug_free; you can also use realloc and free if you do not want debug information about the operation.

A heap-specific version (_debug_ucalloc) is available. _debug_calloc always allocates memory from the default heap.

Return Value
_debug_calloc returns a pointer to the reserved space. If not enough memory is available, or if num or size is 0, _debug_calloc returns NULL.

Example
This example reserves storage of 100 bytes. It then attempts to write to storage that was not allocated. When _debug_calloc is called again, _heap_check detects the error, generates several messages, and stops the program.

Note: You must compile this example with the -qheapdebug option to map the calloc calls to _debug_calloc.

#include <stdlib.h>
#include <stdio.h>
#include <string.h>

int main(void)
{
   char *ptr1, *ptr2;

   if (NULL == (ptr1 = (char*)calloc(1, 100))) {
      puts("Could not allocate memory block.");
      exit(EXIT_FAILURE);
   }
   memset(ptr1, 'a', 105);         /* overwrites storage that was not allocated */
   ptr2 = (char*)calloc(2, 20);      /* this call to calloc invokes _heap_check */
   puts("_debug_calloc did not detect that a memory block was overwritten.");
   return 0;

   /****************************************************************************
      The output should be similar to:

      End of allocated object 0x00073890 was overwritten at 0x000738f4.
      The first eight bytes of the memory block (in hex) are: 6161616161616161.
      This memory block was (re)allocated at line number 9 in _debug_callo.c.
      Heap state was valid at line 9 of _debug_callo.c.
      Memory error detected at line 14 of _debug_callo.c.
   ****************************************************************************/
}

Debugging Memory Heaps
Memory Management Functions
Managing Memory with Multiple Memory Heaps

Debugging Problems with Heap Memory

-qheapdebug Compiler Option
_debug_free - Free Allocated Memory
_debug_heapmin - Free Unused Memory in the Default Heap
_debug_malloc - Allocate Memory
_debug_memcpy - Copy Bytes
_debug_memmove - Copy Bytes
_debug_memset - Set Bytes to Value
_debug_realloc - Reallocate Memory Block
_debug_strcat - Concatenate Strings
_debug_strcpy - Copy Strings
_debug_strncat - Concatenate Strings
_debug_strncpy - Copy Strings
_debug_strnset - Set Characters in String
_debug_strset - Set Characters in String
_debug_ucalloc - Reserve and Initialize Memory from User Heap
_debug_uheapmin - Free Unused Memory in User Heap
_debug_umalloc - Reserve Memory Block from User Heap