Mine

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


int mprintf (char ** p, const char *format, ...)
{
    va_list arg;
    int done=0;
  
    int len = 0;
    int add_len = 0;
    printf("mprintf: %s\n", format);
    
    /* count old chars */
    if(*p)
        len = strlen(*p);

    /* count leng to add + 1 extra for the '\0' */
    add_len = strlen(format) + 1;
    
    printf("Changing size to %i\n", len + add_len);
    *p=realloc(*p, ((len + add_len) * sizeof(char)));

    while(1)
    {
	va_start (arg, format);
	done = vsnprintf ((*p)+len, add_len, format, arg);
	va_end (arg);
	
	/* check if that was enouth */
	if(done > -1 && done < add_len)
	{
	    printf("GOOD: done : %i, len: %i\n", done, add_len);
	    return(done);
	}
	printf("BAD: done : %i, len: %i\n", done, add_len);

	/* try increase it a bit. */
	add_len = ( done < 0 ? add_len * 2 : done + 1);
	printf("Changing size to %i\n", len + add_len);
	*p=realloc(*p, ((len + add_len) * sizeof(char)));
	
    }
    return(-1);
}


int main(int argc, char **argv)
{
    char *test=NULL;

    mprintf(&test, "Hello world\n");
    mprintf(&test, "This is a funny test\n");
    mprintf(&test, "Of an self reallocating function\n");
    mprintf(&test, "that shud work with %s\n", "variables");


    printf("This is test (%i): \n\"%s\"\n", strlen(test), test);

    free(test);
    exit(0);
}