Debugging Memory Heaps
Memory Management Functions
Managing Memory with Multiple Memory Heaps
Format
#include <stdlib.h> /* also in <malloc.h> */ int _debug_heapmin(const char *file, size_t line);
Language Level: Extension
_debug_heapmin is the debug version of _heapmin. Like _heapmin, it returns all unused memory from the default runtime heap to the operating system.
In addition, _debug_heapmin makes an implicit call to _heap_check, and stores the file name file and the line number line where the memory is returned. This information can be used later by the _heap_check function.
To use _debug_heapmin, you must compile with the debug memory -qheapdebug compiler option. This option maps all _heapmin calls to _debug_heapmin.
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.
A heap-specific version of this function (_debug_uheapmin) is also available. _debug_heapmin always operates on the default heap.
Return Value
If successful, _debug_heapmin returns
0; otherwise, it returns -1.
Example
This example allocates 10000 bytes of storage, changes
the storage size to 10 bytes, and then uses _debug_heapmin
to return the unused memory to the operating system. The program
then attempts to overwrite memory that was not allocated. When _debug_heapmin
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 _heapmin calls to _debug_heapmin.
#include <stdlib.h> #include <stdio.h>
int main(void)
{
char *ptr;
/* Allocate a large object from the system */
if (NULL == (ptr = (char*)malloc(100000))) {
puts("Could not allocate memory block.");
exit(EXIT_FAILURE);
}
ptr = (char*)realloc(ptr, 10);
_heapmin(); /* No allocation problems to detect */
*(ptr - 1) = 'a'; /* Overwrite memory that was not allocated */ _heapmin(); /* This call to _heapmin invokes _heap_check */
puts("_debug_heapmin did not detect that a non-allocated memory block"
"was overwritten.");
return 0;
/****************************************************************************
Possible output is:
Header information of object 0x000738b0 was overwritten at 0x000738ac.
The first eight bytes of the memory block (in hex) are: AAAAAAAAAAAAAAAA.
This memory block was (re)allocated at line number 13 in _debug_heapm.c.
Heap state was valid at line 14 of _debug_heapm.c.
Memory error detected at line 17 of _debug_heapm.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_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
