从文件中读取行，遍历每一行和该行中的每个字符

Question

我需要读取一个文件，获取每一行，遍历每一行并检查该行是否包含来自“aeiuo”的任何字符，以及它是否包含至少 2 个字符“äüö”。

这段代码是 Rust 惯用的吗？如何检查 String 中的多个字符？

到目前为止，我尝试了一些 Google 和代码窃取：

use std::error::Error;
use std::fs::File;
use std::io::BufReader;
use std::io::prelude::*;
use std::path::Path;

fn main() {
    // Create a path to the desired file
    let path = Path::new("foo.txt");
    let display = path.display();

    // Open the path in read-only mode, returns `io::Result<File>`
    let file = match File::open(&path) {
        // The `description` method of `io::Error` returns a string that describes the error
        Err(why) => panic!("couldn't open {}: {}", display, Error::to_string(&why)),
        Ok(file) => file,
    };

    // Collect all lines into a vector
    let reader = BufReader::new(file);
    let lines: Vec<_> = reader.lines().collect();

    for l in lines {
        if (l.unwrap().contains("a")) {
            println!("here is a");
        }
    }
}

(Playground link)

Answer 1

1) "Is this code idiomatic Rust?"

总的来说是的，看起来不错。您可能想要改进一个小点：您不需要将线收集到向量中以对其进行迭代。这是不需要的，因为它会触发不需要的内存分配。直接读取 lines() 迭代器就可以了。（如果你来自 C++，你可以忘记将东西收集到中间向量中：想想功能，想想迭代器！）

let reader = BufReader::new(file);
let lines: Vec<_> = reader.lines().collect();

for l in lines {
    ...
}

变成

let reader = BufReader::new(file);
let lines = reader.lines(); 
// lines is a instance of some type which implements Iterator<Item=&str>

for l in lines {
    ...
}

2) "How do I check for several characters in a string?"

我建议基于 .any() 的简单方法：

fn is_aeiou(x: &char) -> bool {
    "aeiou".chars().any(|y| y == *x)
}

fn is_weird_auo(x: &char) -> bool {
    "äüö".chars().any(|y| y == *x)
}

fn valid(line: &str) -> bool {
    line.chars().any(|c| is_aeiou(&c)) &&
    line.chars().filter(is_weird_auo).fuse().nth(1).is_some()
}

然后你就可以一直使用迭代器并编写你的主要测试如下：

let reader = BufReader::new(file);
let lines = reader.lines();

let bad_line = lines.map(|l| l.unwrap()).filter(|line| !valid(line)).next();
match bad_line {
    Some(line_n) => println!("Line {} doesn't pass the test", line_n),
    None => println!("All lines are good!"),
}

// Alternate way if you don't need the line number. More readable
//let all_good = lines.map(|l| l.unwrap()).all(valid);

（playground 上的完整代码。）

Answer 2

这个有效：

use std::error::Error;
use std::fs::File;
use std::io::BufReader;
use std::io::prelude::*;
use std::path::Path;

fn is_vowel(x: &char) -> bool {
    "aAeEiIoOuU".chars().any(|y| y == *x)
}

fn is_umlaut(x: &char) -> bool {
    "äÄüÜöÖ".chars().any(|y| y == *x)
}

fn valid(line: &str) -> bool {
    line.chars().all(|c| !is_vowel(&c)) && line.chars().filter(is_umlaut).fuse().nth(1).is_some()
}

fn main() {
    // Create a path to the desired file
    let path = Path::new("c.txt");
    let display = path.display();
    // Open the path in read-only mode, returns `io::Result<File>`
    let file = match File::open(&path) {
        Err(why) => panic!("couldn't open {}: {}", display, Error::description(&why)),
        Ok(file) => file,
    };
    let reader = BufReader::new(file);
    for line in reader.lines() {
        match line {
            Ok(line) => {
                if valid(&line) {
                    println!("{}", line)
                }
            }
            Err(e) => println!("ERROR: {}", e),
        }
    }
}

从文件中读取行，遍历每一行和该行中的每个字符

Read lines from file, iterate over each line and each character in that line

loops

contains

character

line

rust

1) "Is this code idiomatic Rust?"

2) "How do I check for several characters in a string?"