#define _GNU_SOURCE
#include <pwd.h>
#include <stdio.h>
#include <unistd.h>

char* cuserid(char* buf) {
    struct passwd pw, *ppw;
    long pwb[256];
    if (getpwuid_r(geteuid(), &pw, (void*)pwb, sizeof pwb, &ppw))
        return 0;
    snprintf(buf, L_cuserid, "%s", pw.pw_name);
    return buf;
}