查找从给定索引开始的字符串 [英] Find a string starting from given index

问题描述

如果我不需要从 0 开始，如何找到子字符串的正确方法是什么?

What is the correct way how to find a substring if I need to start not from 0?

我有这个代码:

fn SplitFile(reader: BufReader<File>) {
  for line in reader.lines() {
    let mut l = line.unwrap();
    // l contains "06:31:53.012   index0:2015-01-06 00:00:13.084
    ...

我需要找到第三个 : 并解析它后面的日期.仍然不知道该怎么做，因为 find 没有像 begin 这样的任何参数 - 请参阅 https://doc.rust-lang.org/std/string/struct.String.html#method.find.

I need to find third : and parse the date behind it. Still no idea how to do it, because find doesn't have any param like begin - see https://doc.rust-lang.org/std/string/struct.String.html#method.find.

(我知道我可以使用正则表达式.我已经完成了，但我想比较性能 - 手动解析是否比使用正则表达式更快.<​​/em>)

(I know I can use regex. I have it done, but I'd like to compare the performance - whether parsing by hand might the quicker than using regex.)

推荐答案

您说得对，在搜索字符串时似乎没有任何简单的方法可以跳过多个匹配项.不过，您可以手动完成.

You are right, there doesn't appear to be any trivial way of skipping several matches when searching a string. You can do it by hand though.

fn split_file(reader: BufReader<File>) {
    for line in reader.lines() {
        let mut l = &line.as_ref().unwrap()[..]; // get a slice
        for _ in 0..3 {
            if let Some(idx) = l.find(":") {
                l = &l[idx+1..]
            } else {
                panic!("the line didn't have enough colons"); // you probably shouldn't panic
            }
        }
        // l now contains the date
        ...

更新:

正如 faiface 指出的那样 下面，你可以用splitn()来更简洁:

As faiface points out below, you can do this a bit cleaner with splitn():

fn split_file(reader: BufReader<File>) {
    for line in reader.lines() {
        let l = line.unwrap();
        if let Some(datetime) = l.splitn(4, ':').last() {
            // datetime now contains the timestamp string
            ...
        } else {
            panic!("line doesn't contain a timestamp");
        }
    }
}

你应该给他的答案点赞.

You should go upvote his answer.

这篇关于查找从给定索引开始的字符串的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！