无法将文件内容读取到字符串 - 结果未在名为“read_to_string"的范围内实现任何方法 [英] Unable to read file contents to string - Result does not implement any method in scope named `read_to_string`

问题描述

我按照代码打开了来自 Rust by Example 的文件:

I followed the code to open a file from Rust by Example:

use std::{env, fs::File, path::Path};

fn main() {
    let args: Vec<_> = env::args().collect();
    let pattern = &args[1];

    if let Some(a) = env::args().nth(2) {
        let path = Path::new(&a);
        let mut file = File::open(&path);
        let mut s = String::new();
        file.read_to_string(&mut s);
        println!("{:?}", s);
    } else {
        //do something
    }
}

但是，我收到了这样的消息:

However, I got a message like this:

error[E0599]: no method named `read_to_string` found for type `std::result::Result<std::fs::File, std::io::Error>` in the current scope
  --> src/main.rs:11:14
   |
11 |         file.read_to_string(&mut s);
   |              ^^^^^^^^^^^^^^ method not found in `std::result::Result<std::fs::File, std::io::Error>`

我做错了什么?

推荐答案

让我们看看你的错误信息:

Let's look at your error message:

error[E0599]: no method named `read_to_string` found for type `std::result::Result<std::fs::File, std::io::Error>` in the current scope
  --> src/main.rs:11:14
   |
11 |         file.read_to_string(&mut s);
   |              ^^^^^^^^^^^^^^ method not found in `std::result::Result<std::fs::File, std::io::Error>`

错误消息几乎就是它在罐头上所说的 - 类型 Result 确实没有方法read_to_string.这实际上是 一个关于 trait Read.

The error message is pretty much what it says on the tin - the type Result does not have the method read_to_string. That's actually a method on the trait Read.

你有一个 Result 因为 File::open(&path) 可以失败.失败用 Result 类型表示.Result 可以是 Ok，这是成功案例，或者是 Err，失败案例.

You have a Result because File::open(&path) can fail. Failure is represented with the Result type. A Result may be either an Ok, which is the success case, or an Err, the failure case.

您需要以某种方式处理失败情况.最简单的方法是使用 expect:

You need to handle the failure case somehow. The easiest is to just die on failure, using expect:

let mut file = File::open(&path).expect("Unable to open");

您还需要将 Read 带入范围才能访问 read_to_string:

You'll also need to bring Read into scope to have access to read_to_string:

use std::io::Read;

我强烈推荐通读Rust 编程语言 并执行示例.带有Result的可恢复错误一章代码> 将是高度相关的.我认为这些文档是一流的！

I'd highly recommend reading through The Rust Programming Language and working the examples. The chapter Recoverable Errors with Result will be highly relevant. I think these docs are top-notch!

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