Rust 循环
loop / while / for、循环标签、以及 `loop` 的返回值。
Key Points`loop` 是无限循环，可以用 `break 值` 把结果带出来。
三种循环
Rust
fn main() {
// for：遍历迭代器（最常用）
for i in 1..=3 {
print!("{} ", i);
}
println!();
// while：条件为真时循环
let mut n = 3;
while n > 0 {
print!("{} ", n);
n -= 1;
}
println!();
// loop：无限循环，靠 break 退出
let mut count = 0;
loop {
count += 1;
if count == 3 {
break;
}
}
println!("{}", count);
}Output
1 2 3
3 2 1
3loop 带返回值
Rust
fn main() {
let mut n = 1;
let result = loop {
n *= 2;
if n > 100 {
break n; // 把值带出来
}
};
println!("{}", result);
}Output
128loop is the only loop that yields a value: break n becomes the value of the whole expression. That removes the need for a pre-declared mut holder.
区间
Rust
fn main() {
for i in 0..3 { print!("{} ", i); } // 0 1 2
println!();
for i in 0..=3 { print!("{} ", i); } // 0 1 2 3
println!();
for i in (0..10).step_by(3) { print!("{} ", i); } // 0 3 6 9
println!();
for i in (1..=5).rev() { print!("{} ", i); } // 5 4 3 2 1
println!();
}Output
0 1 2
0 1 2 3
0 3 6 9
5 4 3 2 1 | Form | Meaning |
|---|---|
a..b | 左闭右开 |
a..=b | 左闭右闭 |
..b / a.. | 省略一端 |
.. | 整个范围（用于切片） |
标签
Rust
fn main() {
'outer: for i in 0..3 {
for j in 0..3 {
if i * j == 2 {
println!("找到 {} {}", i, j);
break 'outer;
}
}
}
// continue 也可以带标签
'a: for i in 0..3 {
for j in 0..3 {
if j == 1 {
continue 'a;
}
print!("({},{}) ", i, j);
}
}
println!();
}Output
找到 1 2
(0,0) (1,0) (2,0) Labels start with a quote and sit before the loop. break 'outer exits the outer loop directly — the idiomatic way out of nesting, cleaner than a flag variable.
遍历容器
Rust
fn main() {
let v = vec![10, 20, 30];
// 按值遍历（消费 v）
for x in v {
print!("{} ", x);
}
println!();
let v2 = vec![1, 2, 3];
// 按引用遍历（不消费）
for x in &v2 {
print!("{} ", x);
}
println!();
// 按可变引用（可改）
let mut v3 = vec![1, 2, 3];
for x in &mut v3 {
*x *= 2;
}
println!("{:?}", v3);
}Output
10 20 30
1 2 3
[2, 4, 6]for x in v **moves v** (unusable afterwards). Use for x in &v to keep it. This is the most common source of "value moved here" errors.三种循环
Rust
fn main() {
// for：遍历迭代器（最常用）
for i in 1..=3 {
print!("{} ", i);
}
println!();
// while：条件为真时循环
let mut n = 3;
while n > 0 {
print!("{} ", n);
n -= 1;
}
println!();
// loop：无限循环，靠 break 退出
let mut count = 0;
loop {
count += 1;
if count == 3 {
break;
}
}
println!("{}", count);
}Output
1 2 3
3 2 1
3loop 带返回值
Rust
fn main() {
let mut n = 1;
let result = loop {
n *= 2;
if n > 100 {
break n; // 把值带出来
}
};
println!("{}", result);
}Output
128loop 是唯一能返回值的循环。break n 的值成为整个 loop 表达式的值。这让「一直试到成功」的逻辑不用先声明一个 mut 变量再赋值。
区间
Rust
fn main() {
for i in 0..3 { print!("{} ", i); } // 0 1 2
println!();
for i in 0..=3 { print!("{} ", i); } // 0 1 2 3
println!();
for i in (0..10).step_by(3) { print!("{} ", i); } // 0 3 6 9
println!();
for i in (1..=5).rev() { print!("{} ", i); } // 5 4 3 2 1
println!();
}Output
0 1 2
0 1 2 3
0 3 6 9
5 4 3 2 1 | 写法 | 含义 |
|---|---|
a..b | 左闭右开 |
a..=b | 左闭右闭 |
..b / a.. | 省略一端 |
.. | 整个范围（用于切片） |
标签
Rust
fn main() {
'outer: for i in 0..3 {
for j in 0..3 {
if i * j == 2 {
println!("找到 {} {}", i, j);
break 'outer;
}
}
}
// continue 也可以带标签
'a: for i in 0..3 {
for j in 0..3 {
if j == 1 {
continue 'a;
}
print!("({},{}) ", i, j);
}
}
println!();
}Output
找到 1 2
(0,0) (1,0) (2,0) 标签以单引号开头，紧贴循环。break 'outer 直接跳出外层循环——这是 Rust 处理嵌套循环的标准做法，比用标志变量干净。
遍历容器
Rust
fn main() {
let v = vec![10, 20, 30];
// 按值遍历（消费 v）
for x in v {
print!("{} ", x);
}
println!();
let v2 = vec![1, 2, 3];
// 按引用遍历（不消费）
for x in &v2 {
print!("{} ", x);
}
println!();
// 按可变引用（可改）
let mut v3 = vec![1, 2, 3];
for x in &mut v3 {
*x *= 2;
}
println!("{:?}", v3);
}Output
10 20 30
1 2 3
[2, 4, 6]for x in v **会把 v 移走**（v 之后不能再用）。想保留就用 for x in &v。这是 Rust 新手最常见的「value moved here」报错来源。