The following code ought to work on my (Linux) system, except that it's thinking the characters given in the example aren't printable - and are hence given a length of -1. My manual says "The behaviour of wcwidth depends on the LC_CTYPE category of the current locale", but gives no hint on what to set it to.

$ cat ./uu
#!/usr/bin/perl

use 5.010;

use strict;
use warnings;

use Inline 'C';

my $s0 = "Hello, world";
my $s1 = "\x{5fcd}\x{65e0}\x{53ef}\x{5fcd}";
my $s2 = "($s1)";

my $l0 = w_length ($s0);
my $l1 = w_length ($s1);
my $l2 = w_length ($s2);

say "$l0: $s0";
say "$l1: $s1";
say "$l2: $s2";

__END__
__C__
#include <wchar.h>
int w_length(char* str) {
    int i;
    int length;
    char c;
    i = 0;
    length = 0;
    while(c = str[i++]) {
        int l;
        l = wcwidth(c);
        length += l > 0 ? l : 0;
    }
    return length;
}
$ LC_CTYPE=en_US.UTF-8 perl -CO ./uu
12: Hello, world
[download]

So, there's something missing in my solution, but I'm far from a Unicode expert, let alone the provided library on my system, but it maybe something you can use as a start.