《The Rust Programming Language》的Rust 学习 1

最近开始学Rust了，主要看《The Rust Programming Language》，个人感觉《Rust by example》不适合小白，到结构体哪里的题就已经不会做了。慢慢更新这个帖子。

2.Programming a Guessing Game

作者给的代码

   let mut guess = String::new();

    io::stdin()
        .read_line(&mut guess)
        .expect("Failed to read line");

    let guess: u32 = guess.trim().parse().expect("Please type a number!");

    println!("You guessed: {}", guess);

    match guess.cmp(&secret_number) {
        Ordering::Less => println!("Too small!"),
1
2
3
4
5
6
7
8
9
10
11
12

我的想法是把secret_number转成String和guess比较

    println!("{}",&(&secret_number).to_string());
    let mut guess = String::new();
    io::stdin()
        .read_line(&mut guess)
        .expect("input error");
    //let guess : u32 = guess.trim().parse().expect("");
    println!("You guessed: {}", guess);

    match guess.cmp(&(&secret_number).to_string()) {
        Ordering::Less => println!("Too small!"),
1
2
3
4
5
6
7
8
9
10

虽然可以编译过，但是运行结果不对

用 gdb调试了一下
display 发现 两个string缺一个/n

最终改写为

        let secret_number = rand::thread_rng().gen_range(1, 101);
        let mut secret_number : String = secret_number.to_string();
        secret_number.push_str("\n");
    ........
        match guess.cmp(&secret_number) {
                  Ordering::Less => println!("Too small!"),
1
2
3
4
5
6

成功了

之前没有注意这个

 println!("You guessed: {}", guess);
1

这一行输出有空格。。。

文章中也说了输入带空格的问题

We bind guess to the expression guess.trim().parse(). The guess in the expression refers to the original guess that was a String with the input in it. The trim method on a String instance will eliminate any whitespace at the beginning and end. Although u32 can contain only numerical characters, the user must press enter to satisfy read_line. When the user presses enter, a newline character is added to the string. For example, if the user types 5 and presses enter, guess looks like this: 5\n. The \n represents “newline,” the result of pressing enter. The trim method eliminates \n, resulting in just 5.
所以在作者的代码

  let guess: u32 = guess.trim().parse().expect("Please type a number!");
1

trim()删除 \n
parse()将 String类型的变量转化为指定类型

因此简单点就行

match guess.trim().cmp(&(&secret_number).to_string()) {
     Ordering::Less => println!("Too small!"),
1
2