为什么在将大于i32的数字存储到变量中时，我没有得到文字超出范围错误？

Posted 2021-05-05

Rust文档说默认的整数类型是i32，这意味着变量默认保存的最大数字是2147483647，即2e31 - 1。结果也是如此：如果我试图在2e31 - 1变量中保存比x更多的数字，我得到错误literal out of range。

码

fn main() {
    let x = 2147483647;
    println!("Maximum signed integer: {}", x);
    let x = 2e100;
    println!("x evalues to: {}", x);
}

但如果我在2e100变量中保存值x，为什么我不会得到错误？它肯定会评估大于2e31 - 1。

产量

Maximum signed integer: 2147483647
x evalues to: 20000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000

码

fn main() {
    let x = 2147483648;
    println!("Maximum signed integer: {}", x);
}

产量

error: literal out of range for i32
 --> src/main.rs:2:11
  |
2 |     let x=2147483648;
  |           ^^^^^^^^^^
  |
  = note: #[deny(overflowing_literals)] on by default

答案

像2e100这样的常量文字不是整数文字，而是浮点文字。这可以显示

fn main() {
    let () = 2e100;
}

哪个产生

error[E0308]: mismatched types
 --> src/main.rs:2:9
  |
2 |     let () = 2e100;
  |         ^^ expected floating-point number, found ()
  |
  = note: expected type `{float}`
             found type `()`

也可以看看：

• How do I print the type of a variable in Rust?