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;
}

What do you mean, 'how do you do it'?

Code:

void *fmalloc( size_t s )
{
    return malloc( s );
}

I don't understand what you aren't knowing how to do.

"Bob, I can 'do that code' in one line!"
"Quzah, do that code!"

#define fmalloc malloc

[edit]
I misunderstoold what you had intended. You shouldn't try and override standard functions. I mean I guess you can try, but it's bad practice. Especially if you're going to try and have reusable code at all.
[/edit]



Quzah.

Maybe something like the following would work.

Code:

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

void *fmalloc(size_t size)
{
   void *start = malloc(size);
   if(start)
   {
      char *end = start;
      end += size;
      printf("fmalloc:%p-%p\n", start, end);
   }
   else
   {
      puts("fmalloc failed");
   }
   return(start);
}

#define malloc fmalloc

int main()
{
   char *ptr = malloc(64);
   free(ptr);
   return 0;
}

/* my output
fmalloc:007A305C-007A309C
*/

I don't see anything too wrong with writing your own malloc. However, of the standard library functions malloc is probably the most frustrating to write.

>I don't see anything too wrong with writing your own malloc.
I do. Without very careful planning and use of a standard memory allocation routine you lose any vestige of portability. Writing a wrapper is far better:

Code:

void *fmalloc ( size_t size )
{
  void *new_block;

  new_block = malloc ( size );
  if ( new_block == NULL ) {
    fputs ( "Error allocating memory\n", stderr );
    exit ( EXIT_FAILURE ); /* Or your favorite recovery routinte */
  }

  return new_block;
}

-Prelude