Thread: malloc & cover function

I want to write a cover function for malloc, so that each time malloc() is invoked, the program execute fmalloc() instead. In fmalloc() I will execute the real malloc(). How do I do that??

Code:

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

int main (void)
{
	char *pt,*lt,*gt;
	
	pt=(char*)malloc(40);
	if (pt==NULL)
		{
		perror("fmalloc");
		exit(1);
		}
	
	lt=(char*)malloc(40);
	if (lt==NULL)
		{
		perror("fmalloc");
		exit(1);
		}

	gt=(char*)malloc(40);
	if (gt==NULL)
		{
		perror("fmalloc");
		exit(1);
		}

	strcpy(pt, "abcdefghijklmnopqrstuvxyz");
	strcpy(lt, "abcdefghijklmnopqrstuvxyz");
	strcpy(gt, "abcdefghijklmnopqrstuvxyz");


	printf("Address allocated is %p\n",pt);
	printf("Address allocated is %p\n",lt);
	printf("Address allocated is %p\n",gt);

	free(pt);
	free(lt);
	free(gt);

	printf("Address freed is %p\n",pt);
	printf("Address freed is %p\n",lt);
	printf("Address freed is %p\n",gt);
	
	return 0;
}