逐行读取文件时“借来的值不够长”

Question

当逐行读取文件时，我有一些借用问题。 如何在此代码中将借用值（ line_ok ）转换为拥有？

运行以下代码时：

use std::fs::{File};
use std::io::{BufRead, BufReader,Lines,Error};

fn read_lines(filename: &str) -> Result<Lines<BufReader<File>>, Error>{
    let file = File::open(filename)?;
    Ok(BufReader::new(file).lines())
}

fn main() {
    let values1=vec!["a","asd"];
    let values2=vec!["b","csd"];
    let file_path="file.txt";

    if let Ok(reader)=read_lines(file_path){
        let mut previous : Option<&str>= None;
        for line in reader {//["a","ab","b","cb","asd","csd"]
            if let Ok(line_ok)=line{
                if values1.contains(&line_ok.as_str()){
                    previous=Some(&line_ok);
                }
                else if values2.contains(&line_ok.as_str()){
                    if previous.is_some(){
                        println!("{} is {}",previous.unwrap(),line_ok);
                    }
                    previous=None;
                }
            }
        }
    }

}

我收到以下错误：

    error[E0597]: `line_ok` does not live long enough
  --> src\main.rs:19:35
   |
19 |                     previous=Some(&line_ok);
   |                                   ^^^^^^^^ borrowed value does not live long enough
...
22 |                     if previous.is_some(){
   |                        -------- borrow later used here
...
27 |             }
   |             - `line_ok` dropped here while still borrowed

Answer 1

Lines是io::Result<String>的迭代器。 您不能存储对此迭代器生成的字符串的引用，因为它将在下一次迭代中从 scope 中取出 go。 您可以将previous的类型更改为Option<String>以使其工作。

use std::fs::File;
use std::io::{BufRead, BufReader, Error, Lines};

fn read_lines(filename: &str) -> Result<Lines<BufReader<File>>, Error> {
    let file = File::open(filename)?;
    Ok(BufReader::new(file).lines())
}

fn main() {
    let values1 = vec!["a", "asd"];
    let values2 = vec!["b", "csd"];
    let file_path = "file.txt";

    if let Ok(reader) = read_lines(file_path) {
        let mut previous: Option<String> = None;
        for line in reader {
            //["a","ab","b","cb","asd","csd"]
            if let Ok(line_ok) = line {
                if values1.contains(&line_ok.as_str()) {
                    previous = Some(line_ok);
                } else if values2.contains(&line_ok.as_str()) {
                    if let Some(prev) = previous {
                        println!("{} is {}", prev, line_ok);
                    }
                    previous = None;
                }
            }
        }
    }
}