1#define _GNU_SOURCE
 2#include <pwd.h>
 3#include <stdio.h>
 4#include <unistd.h>
 5#include <string.h>
 6
 7char *cuserid(char *buf)
 8{
 9	static char usridbuf[L_cuserid];
10	struct passwd pw, *ppw;
11	long pwb[256];
12	if (buf) *buf = 0;
13	getpwuid_r(geteuid(), &pw, (void *)pwb, sizeof pwb, &ppw);
14	if (!ppw)
15		return buf;
16	size_t len = strnlen(pw.pw_name, L_cuserid);
17	if (len == L_cuserid)
18		return buf;
19	if (!buf) buf = usridbuf;
20	memcpy(buf, pw.pw_name, len+1);
21	return buf;
22}