How to convert Rust strings to UTF-16?

Question

Editor's note: This code example is from a version of Rust prior to 1.0 and is not valid Rust 1.0 code, but the answers still contain valuable information.

I want to pass a string literal to a Windows API. Many Windows functions use UTF-16 as the string encoding while Rust's native strings are UTF-8.

I know Rust has utf16_units() to produce a UTF-16 character iterator, but I don't know how to use that function to produce a UTF-16 string with zero as last character.

I'm producing the UTF-16 string like this, but I am sure there is a better method to produce it:

extern "system" {
    pub fn MessageBoxW(hWnd: int, lpText: *const u16, lpCaption: *const u16, uType: uint) -> int;
}

pub fn main() {
    let s1 = [
        'H' as u16, 'e' as u16, 'l' as u16, 'l' as u16, 'o' as u16, 0 as u16,
    ];
    unsafe {
        MessageBoxW(0, s1.as_ptr(), 0 as *const u16, 0);
    }
}

Answer 1

Rust 1.46+

For static UTF-16 strings, the utf16_lit crate provides an easy to use macro to do this at compile time:

use utf16_lit::utf16_null;

fn main() {
    let s = &utf16_null!("Hello");
    println!("{:?}", s);
}