Introduction.

$LASTSAVEDBY indicates the name of the user who have saved the file for last time.
The user can be detect with the command "whoami" used on more Operating Systems, but for insert it in a C program is better to use:

/* whoami raplace program
Author: Copyright (C) 2014 by Paolo Caroni
License: GPLv2 or any later versions*/

#include <stdio.h>

int main(void)
{
   printf("%s\n", getenv("USER"));


   return 0;
}