Implement Display for png_image

rust/coffi/src/main.rs

    message: [u8; 64],
}
impl std::fmt::Display for png_image {
    fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
        fn get_message(msg: [u8; 64]) -> String {
            let mut vec = Vec::new();
            for i in 0..64 {
                vec.push(msg[i]);
            }
            String::from_utf8(vec).unwrap()
        }
        write!(f, "{}x{} {} {} {} {} {} {}", self.width, self.height, self.version,
               self.format, self.flags, self.colormap_entries, self.warning_or_error,
               get_message(self.message))
    }
}
#[link(name = "png")]
extern {
    fn png_image_begin_read_from_file(img: *mut png_image, file_name: *const u8) -> libc::c_int;
    let x = unsafe { cos(3.1415) };
    println!("cos(3.1415) = {}", x);
    fn get_message(msg: [u8; 64]) -> String {
        let mut vec = Vec::new();
        for i in 0..64 {
            vec.push(msg[i]);
        }
        String::from_utf8(vec).unwrap()
    }
    fn print_img(img: &png_image) {
        println!("{}x{} {} {} {} {} {} {}", img.width, img.height, img.version, img.format, img.flags, img.colormap_entries, img.warning_or_error, get_message(img.message))
    }
    unsafe {
        let mut img: png_image = std::mem::zeroed();
        img.version = 1;
        print_img(&img);
        println!("{}", img);
        let res = png_image_begin_read_from_file(&mut img, "mei.png\0".as_ptr());
        println!("read_from_file: {}", res);
        print_img(&img);
        println!("{}", img);
    }
}