文章目录
一、错误处理之：Result、Option以及panic!宏
Rust中的错误可以分为两种
-
Recoverable error：有返回类型
（1）返回Result类型
（2）返回Option类型
-
Unrecoverable type：没有返回类型，直接崩溃
panicmacro将终止当前线程
1.Result
Result是一个枚举类型，有两个变体：0k和Err。它通常用于表示函数的执行结果，其中ok表示成功的结果，Err表示出现了错误
rust
pub enum Result<T，E>{
Ok(T)，
Err (E),
}2.Option
·Option也是一个枚举类型，有两个变体：Some和None。它通常用于表示一个可能为空的值。
rust
pub enum Option<T>{
None,
Some (T),
}3.panic!
当程序遇到无法继续执行的错误时，可以使用panic！宏来引发恐慌。恐慌会导致程序立即终止，并显示一条错误消息。
Example：
rust
fn divide(a: i32, b: i32) -> Result<f64, String> {
if b == 0 {
return Err(String::from("cannot be zero"));
}
let a = a as f64;
let b = b as f64;
Ok(a / b)
}
fn find_element(array: &[i32], target: i32) -> Option<usize> {
for (index, element) in array.iter().enumerate() {
if (*element) == target {
return Some(index);
}
}
None
}
fn main() {
// 处理result结果只能使用match
match divide(1, 2) {
Ok(number) => println!("{}", number),
Err(err) => println!("{}", err),
}
match divide(1, 0) {
Ok(number) => println!("{}", number),
Err(err) => println!("{}", err),
}
// option
let arr = [1, 2, 3, 4, 5];
match find_element(&arr, 4) {
Some(index) => println!("found in {}", index),
None => println!("None"),
}
match find_element(&arr, 7) {
Some(index) => println!("found in {}", index),
None => println!("None"),
}
// panic
let vec = vec![1, 2, 3, 4, 5];
vec[43]; //数组越界
}编译及运行：
bash
cargo run
Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.00s
Running `target/debug/ch17_error`
0.5
cannot be zero
found in 3
None
thread 'main' panicked at src/main.rs:43:8:
index out of bounds: the len is 5 but the index is 43
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
~/installer/rust/project/ch17_error master x101
bash
RUST_BACKTRACE=1 cargo run
Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.00s
Running `target/debug/ch17_error`
0.5
cannot be zero
found in 3
None
thread 'main' panicked at src/main.rs:43:8:
index out of bounds: the len is 5 but the index is 43
stack backtrace:
0: rust_begin_unwind
at /rustc/1e4f10ba6476e48a42a79b9f846a2d9366525b9e/library/std/src/panicking.rs:665:5
1: core::panicking::panic_fmt
at /rustc/1e4f10ba6476e48a42a79b9f846a2d9366525b9e/library/core/src/panicking.rs:75:14
2: core::panicking::panic_bounds_check
at /rustc/1e4f10ba6476e48a42a79b9f846a2d9366525b9e/library/core/src/panicking.rs:285:5
3: <usize as core::slice::index::SliceIndex<[T]>>::index
at /home/wangji/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/core/src/slice/index.rs:304:10
4: core::slice::index::<impl core::ops::index::Index<I> for [T]>::index
at /home/wangji/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/core/src/slice/index.rs:16:9
5: <alloc::vec::Vec<T,A> as core::ops::index::Index<I>>::index
at /home/wangji/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/alloc/src/vec/mod.rs:3344:9
6: ch17_error::main
at ./src/main.rs:43:8
7: core::ops::function::FnOnce::call_once
at /home/wangji/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/core/src/ops/function.rs:250:5
note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.二、错误处理之：unwrap()与'?'
1.unwrap()
注意：该方法并不安全
unwrap（）是 Result 和 Option 类型提供的方法之一。它是一个简便的方法，用于获取 Ok 或 Some 的值，如果是 Err 或 None 则会引发 panic
2.？运算符
？用于简化 Result 或 Option 类型的错误传播。它只能用于返回 Result 或Option 的函数中，并且在函数内部可以像使用unwrap（）一样访问 Ok 或 Some的值，但是如果是 Err 或 None 则会提前返回。
Example：
rust
use std::num::ParseIntError;
fn find_first_even(numbers: Vec<i32>) -> Option<i32> {
let first_even = numbers.iter().find(|&num| num % 2 == 0)?;
print!("Option");
Some(*first_even)
}
// 传递错误
fn parse_numbers(input: &str) -> Result<i32, ParseIntError> {
let val = input.parse::<i32>()?;
Ok(val)
}
fn main() -> Result<(), Box<dyn std::error::Error>> {
// Result<i32, &str>
let result_ok: Result<i32, &str> = Ok(32);
let value = result_ok.unwrap();
println!("{}", value);
// Result<i32, &str> 直接panic
// let result_ok: Result<i32, &str> = Err("ff");
// let value = result_ok.unwrap();
// println!("{}", value);
// 使用?
let result_ok: Result<i32, &str> = Ok(100);
let value = result_ok?;
println!("{}", value);
// 找到第一个偶数
let numbers = vec![1, 3, 5];
match find_first_even(numbers) {
Some(_) => println!("first even 1"),
None => println!("no such number"),
}
match parse_numbers("d") {
Ok(i) => println!("parsed {}", i),
Err(err) => println!("failed to parse: {}", err),
}
Ok(())
}编译及运行：
bash
cargo run
Compiling ch18_question_unwrap v0.1.0 (/home/wangji/installer/rust/project/ch18_question_unwrap)
Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.23s
Running `target/debug/ch18_question_unwrap`
32
100
no such number
failed to parse: invalid digit found in string三、自定义一个Error类型
1.定义错误类型结构体：创建一个结构体来表示你的错误类型，通常包含一些字段来描述错误的详细信息。
2.实现 std::fmt::Display trait：实现这个 trait以定义如何展示错误信息。这是为了使错误能够以人类可读的方式打印出来。
3.实现 std::error::Error trait：实现这个 trait以满足Rust的错误处理机制的要求。
rust
#[derive(Debug)]
struct MyError {
detail: String,
}
impl std::fmt::Display for MyError {
fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
write!(f, "Custom Error: {}", self.detail)
}
}
impl std::error::Error for MyError {
fn description(&self) -> &str {
&self.detail
}
// &String String&自动转=> &str 字符串字面量
}
fn func() -> Result<(), MyError> {
Err(MyError {
detail: "CustomError".to_owned(),
})
// Ok(())
}
// 等价于fn main()->Result<(), MyError>
// 所有实现std::error::Error 的东西，都可以使用Box<dyn std::error::Error>进行返回
fn main() -> Result<(), Box<dyn std::error::Error>> {
match func() {
Ok(_) => println!("func ok"),
Err(err) => println!("Error: {}", err),
}
func()?;
println!("oo"); //以前前面?的原因，且返回的是Err，这里则不会输出
Ok(())
}编译及运行
bash
cargo run
Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.05s
Running `target/debug/ch19_custom_err`
Error: Custom Error: CustomError
Error: MyError { detail: "CustomError" }