This example creates a fixed-size heap myheap and uses _udefault to make it the default heap. The call to malloc then allocates memory from myheap. The second call to _udefault restores the original default heap.
#include <windows.h> #include <stdlib.h> #include <stdio.h> #include <umalloc.h>
int main(void)
{
void *initial_block;
Heap_t myheap, old_heap;
char *p;
/* Call VirtualAlloc to get the initial block of memory */
if (NULL == (initial_block =
VirtualAlloc(NULL, 65536, MEM_COMMIT|MEM_RESERVE, PAGE_READWRITE)))
{
printf("VirtualAlloc error: %d\n.", GetLastError());
exit(EXIT_FAILURE);
}
/* Create a fixed size heap starting with the block declared earlier */
if (NULL == (myheap = _ucreate(initial_block, 65536, _BLOCK_CLEAN,
_HEAP_REGULAR, NULL, NULL))) {
puts("_ucreate failed.");
exit(EXIT_FAILURE);
}
if (0 != _uopen(myheap)) {
puts("_uopen failed.");
exit(EXIT_FAILURE);
}
/* myheap is used as default heap */ old_heap = _udefault(myheap);
/* malloc will allocate memory from myheap */ p = (char *)malloc(100); memset(p, 'x', 10);
/* Restore original default heap */ _udefault(old_heap);
free(p);
if (0 != _uclose(myheap)) {
puts("_uclose failed");
exit(EXIT_FAILURE);
}
if (FALSE == VirtualFree(initial_block, 0, MEM_RELEASE)) {
printf("VirtualFree error: %d\n.", GetLastError());
exit(EXIT_FAILURE);
}
return 0;
}