Rust系统编程之容器

1.vector

1.1 初始化

空数组

let v: Vec<i32> = Vec::new();

含有初始值的数组

let v = vec![1, 2, 3];

1.2 增加元素

末尾增加元素

let mut v = Vec::new();

v.push(5);
v.push(6);
v.push(7);
v.push(8);

1.3 访问元素

索引访问

let v = vec![1, 2, 3, 4, 5];
// 这里要使用引用
let third: &i32 = &v[2];
println!("The third element is {third}");

get方法，可以判断获取是否成功

let v = vec![1, 2, 3, 4, 5];

let third: Option<&i32> = v.get(2);
match third {
    Some(third) => println!("The third element is {third}"),
    None => println!("There is no third element."),
}

1.4 安全问题

let mut v = vec![1, 2, 3, 4, 5];
// get和index都会导致这个问题
let first = &v[0];
v.push(6);
println!("The first element is: {first}");

上述代码编译错误，因为push操作可能会因为内存不够重新申请内存，而这样的话会导致引用无效，编译器不允许。

1.5 遍历数组

let mut v = vec![100, 32, 57];
for i in &mut v {
	*i += 50;
}

1.6 使用枚举来支持多类型元素

enum SpreadsheetCell {
	Int(i32),
	Float(f64),
	Text(String),
}

let row = vec![
	SpreadsheetCell::Int(3),
	SpreadsheetCell::Text(String::from("blue")),
    SpreadsheetCell::Float(10.12),
];

2.string

2.1 初始化

空字符串

let s = String::new();

使用字符串字面值进行初始化

let s = "hello".to_string();

let s = String::from("hello");

2.2 拼接字符串

let mut s = String::from("foo");
s.push_str("bar");

2.3 格式化字符串

let s1 = String::from("tic");
let s2 = String::from("tac");
let s3 = String::from("toe");
let s = format!("{s1}-{s2}-{s3}");

2.4 转数字

let mut s1 = String::from("123");
let num:u32 = s1.parse().unwrap();
println!("s1 is {num}");

3.HashMap

3.1 初始化

use std::collections::HashMap;

let mut scores = HashMap::new();

scores.insert(String::from("Blue"), 10);
scores.insert(String::from("Yellow"), 50);

let team_name = String::from("Blue");
let score = scores.get(&team_name).copied().unwrap_or(0);

3.2 插入元素

hash table插入元素会夺取所有权。

a.覆盖插入

use std::collections::HashMap;

let mut scores = HashMap::new();

scores.insert(String::from("Blue"), 10);
scores.insert(String::from("Blue"), 25);

println!("{:?}", scores);

b.不重复插入

 use std::collections::HashMap;

let mut scores = HashMap::new();
scores.insert(String::from("Blue"), 10);

scores.entry(String::from("Yellow")).or_insert(50);
scores.entry(String::from("Blue")).or_insert(50);

println!("{:?}", scores);

3.2 遍历元素

use std::collections::HashMap;

let mut scores = HashMap::new();

scores.insert(String::from("Blue"), 10);
scores.insert(String::from("Yellow"), 50);

for (key, value) in &scores {
	println!("{key}: {value}");
}