rust16.字符串string

{% note info %}
实际上rust核心中一般使用str类型，很少出现string，这种是在编译库中实现的
{% endnote%}
//1.创建一个空string
//2.通过字面值创建一个string
//2.1 使用string::from()
//2.2 使用str的方式
//3. 更新string
//3.1 push_str
//3.2 push
//3.3 使用"+"合并字符串
//3.4 使用format
//4. string索引
//5. str索引
//6. 遍历
//6.1 chars
//6.2 bytes
fn main() {
    //1.
    let mut s0 = String::new();
    s0.push_str("hello");
    println!("s0 = {}",s0);

    //2.
    //2.1
    let s1 = String::from("init some thing");
    println!("s1 = {}",s1);
    //2.2
    let s1 = "init som thing".to_string();
    println!("s1 = {}",s1);
    //3.
    //3.1
    let mut s2 = String::from("hello");
    s2.push_str(",world");
    println!("s2 = {}",s2);

    let ss = "!".to_string();
    s2.push_str(&ss);//使用ss的引用值
    println!("s2 = {}",s2);
    println!("ss = {}",ss);//并没有拿走字符串ss的所有权
    //3.2
    //push只能添加一个字符
    let mut s2 = String::from("tea");
    s2.push('m');
    //仍然报错，因为双引号代表引用
    //s2.push("mx");
    println!("s2 = {}",s2);
    
    //3.3合并字符串
    let s1 = "hello".to_string;
    let s2 = String::from(",world");
    let s3 = s1 + &s2;
    println!("s3 = {}",s3);
    //s1已经不能够使用，因为s1所有权给了s3
    //println!("s1 = {}",s1);
    println!("s2 = {}",s2);
    //3.4
    let s341 = String::from("tic");
    let s342 = String::from("tac");
    let s343 = String::from("toe");
    let s344 = format!("{}-{}-{}",s341,s342,s343);//format宏和println宏类似，
    //但是format是给到变量，而println!是给到std::out。
    println!("s344 = {}",s344);
    //4.
    let s4 = String::from("hello");
    let s41 = s4[0];//string不能被索引
    println!("s4.len = {}",s4.len());
    
    //使用utf-8编码，所以汉字长度为3个字符
    //没法对齐，所以不能获取索引
    let s4 = String::from("你好");
    println!("s4.len = {}",s4);
    //5.
    //但是使用str(slice)可以
    let hello = "你好";
    let h5 = &hello[0..3];
    println!("h5 = {}",h5);
    //但是不能够取到非边界。
    //let h6 = &hello[0..2];
    //println!("h6 = {}",h6);
    
    //6.
    //chars
    for c in s4.chars() {
        println!("c  = {}",c);
      }
    //bytes
    //按照字节打印
    for b in s4.bytes() {
      println!("b = {}",b);
    }
  }