Expected encoding of wcwidth() argument - c

Question

I'm trying to find out what the expected encoding of wcwidth() argument is.
The man page says absolutely nothing about this, and I wasted hours trying to
find out what it is. Here's an example, in C:
#include <stdio.h>
#include <wchar.h>
void main()
{
wchar_t c = L'ｈ';
printf("%d\n", wcwidth(c));
}
I want to know how should I encode this character literal so that this program
prints 2 instead of -1.
Here's a Rust example:
extern "C" {
fn wcwidth(c: libc::wchar_t) -> libc::c_int;
}
fn main() {
let c = 'ｈ';
println!("{}", unsafe { wcwidth(c as libc::wchar_t) });
}
Similarly I want to convert this character constant to wchar_t (i32) so that
this program prints 2.
Thanks.
UPDATE: Sorry for my wording, I made this sound specific to C's long char literals. I want to encode character literals in any language as a 32-bit int so that when I pass it to wcwidth I get a right answer. So my question is not specific to C or C's long char literals.
UPDATE 2: I'd also be happy with another function like wcwidth that is better specified (and maybe even platform independent). E.g. one that takes UTF-8 encoded character and returns number of cols needed to render it in a monospace terminal.

Answer 1

You need to add support for _XOPEN_SOURCE and also you need to set your locales.
Try this:
#define _XOPEN_SOURCE 700
#include <stdio.h>
#include <locale.h>
#include <wchar.h>
int main(void)
{
setlocale(LC_CTYPE, "");
wchar_t c = L'ｈ';
printf("%d\n", wcwidth(c));
return 0;
}