ref: f90f03a2e03ae243a800e11d6e04a63781940b1f
dir: /sys/src/libc/fmt/vsnprint.c/
#include <u.h>
#include <libc.h>
int
vsnprint(char *buf, int len, char *fmt, va_list args)
{
Fmt f;
if(len <= 0)
return -1;
f.runes = 0;
f.start = buf;
f.to = buf;
f.stop = buf + len - 1;
f.flush = nil;
f.farg = nil;
f.nfmt = 0;
f.args = args;
dofmt(&f, fmt);
*(char*)f.to = '\0';
return (char*)f.to - buf;
}