get_current_username.c

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

int main()
{
    register struct passwd *pw;
    register uid_t uid;

    uid = geteuid(); //Get userID
    pw = getpwuid(uid); //Get userID data

    if(pw)
    {
        //Print username
        printf("Executed as {%s}\n.", pw->pw_name);
        exit(EXIT_SUCCESS);
    }

    fprintf(stderr, "cannot find username for UID %u/n", (unsigned)uid);
    exit(EXIT_FAILURE);
}