无法将文件内容读取为字符串-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

我按照代码从 Rust by Example 打开文件：

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>`

我在做什么错了？

推荐答案

让我们看看您的错误消息：

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>`

错误消息几乎是它在罐子上所说的-类型 结果 不具有方法 read_to_string 。这实际上是关于特征的方法阅读 。

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.

您有一个结果，因为 File :: open（& path）可能失败。失败用 Result 类型表示。 结果可以是 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案例。最简单的方法就是使用 expect 死于失败：

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");

您还需要携带 Read 可以访问 read_to_string ：

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

use std::io::Read;

我会强烈推荐通读 Rust编程语言 并处理示例。 具有的可恢复错误结果 将非常相关。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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