How to work with WINAPI string types.

winapi-conversion.rs

pub fn to_u16s<S: AsRef<OsStr>>(s: S) -> io::Result<Vec<u16>> {
    fn inner(s: &OsStr) -> io::Result<Vec<u16>> {
        let mut maybe_result: Vec<u16> = s.encode_wide().collect();
        if maybe_result.iter().any(|&u| u == 0) {
            return Err(io::Error::new(
                io::ErrorKind::InvalidInput,
                "strings passed to WinAPI cannot contain NULs",
            )
            .into());
        }
        maybe_result.push(0);
        Ok(maybe_result)
    }
    inner(s.as_ref())
}

fn play_sound<S: AsRef<OsStr>>(file_name: S) -> io::Result<WhateverNonErrorTypeYouReturn> {
    //Converts your &str into a Vec<u16>
    let file_name = to_u16s(file_names)?;
    
    //The .as_ptr() call provides a pointer to the Vec<u16>. The pointer is recognized as a LPCWSTR.
    PlaySoundW(file_name.as_mut_ptr(), <other variables>);
    
}