fn main() -> std::io::Result<()> {

    let filename="D:\\text.txt";
    

    let mut filecontent= String::new();
    println!("请输入向文件中写入的内容");
    stdin().read_line(&mut filecontent)
    .expect("Failed to read line.");

    let mut file = OpenOptions::new()
            .append(true).open(&filename)?;

    file.write(filecontent.as_bytes()).expect("write failed");

    Ok(())
}