Debugging Memory Heaps
Memory Management Functions
Managing Memory with Multiple Memory Heaps
Format
#include <string.h>
void *_debug_memmove(void *dest, const void *src, size_t count,
const char *file, size_t line);
Language Level: Extension
_debug_memmove is the debug version of memmove. Like memmove, it copies count bytes of src to dest, and allows for copying between objects that may overlap.
_debug_memmove validates the heap after copying the bytes to the target location, and performs this check only when the target is within a heap. _debug_memmove makes an implicit call to _heap_check. If _debug_memmove detects a corrupted heap when it makes a call to _heap_check, _debug_memmove will report the file name file and line number line in a message.
Note: _debug_memmove checks only the current default heap. Therefore, this debug support will not check all heaps within applications that have multiple user heaps.
To use _debug_memmove, you must compile with the debug memory -qheapdebug compiler option. This option maps all memcpy calls to _debug_memmove. You do not have to change your source code, in order for _debug_memmove to verify the heap.
Note: The -qheapdebug option maps all calls to other string functions and all calls to memory management functions (including a heap-specific version), to their debug counterparts. To prevent a call from being mapped, parenthesize the function name.
Return Value
_debug_memmove returns a pointer to dest.
Example
This example contains a programming error. The count specified on
memmove is 15 instead of 5, and the memmove
operation copies bytes past the end of the allocated object.
#include <stdlib.h> #include <string.h> #include <stdio.h>
#define SIZE 21
int main(void)
{
char *target, *p, *source;
target = (char*)malloc(SIZE);
strcpy(target, "a shiny white sphere");
p = target+8; /* p points at the starting character
of the word we want to replace */
source = target+2; /* start of "shiny" */
printf("Before memmove, target is \"%s\"\n", target);
memmove(p, source, 15);
printf("After memmove, target becomes \"%s\"\n", target);
return 0;
/****************************************************************************
The output should be similar to:
Before memmove, target is "a shiny white sphere"
End of allocated object 0x00073c80 was overwritten at 0x00073c95.
The first eight bytes of the memory block (in hex) are: 61207368696E7920.
This memory block was (re)allocated at line number 11 in memmove.c.
Heap state was valid at line 12 of memmove.c.
Memory error detected at line 18 of memcpy.c.
****************************************************************************/
}
Debugging Memory Heaps
Memory Management Functions
Managing Memory with Multiple
Memory Heaps
Debugging Problems with Heap
Memory
-qheapdebug Compiler
Option
_debug_calloc - Allocate and Initialize
Memory
_debug_free - Free Allocated Memory
_debug_heapmin - Free Unused Memory in the
Default Heap
_debug_malloc - Allocate Memory
_debug_memcpy - 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
