something weird with strerror_r

[CodeSun via Digitalmars-d]

Recently, I found something really weird when I use strerror_t 
function which is declared inside std.c.string.
The code snippet is listed below:
import std.c.string;
import core.stdc.errno;

void main() {
	import std.stdio;
	char[128] buf;
	strerror_r(errno, buf.ptr, buf.sizeof);
	writeln(cast(string)buf);
}

The terminal should print "Success" with errno=0, but in this 
example, the result is 
"��������������������������������������������������������������������������������������������������������������������������������".
I test this snippet both on Archlinux and Ubuntu 14.04.1, and the 
result is same. If there is someone can help me?
I wanna know if it is my mistake or it is just a bug.
Thx!