問題描述

我正在嘗試用不同的替換模式替換字符串中的某些模式.

I am trying to replace certain patterns in a string with different replacement patters.

示例:

string test = "test replacing "these characters"";

我想要做的是將所有的 ' ' 替換為 '_'，并將所有其他非字母或數(shù)字字符替換為空字符串.我創(chuàng)建了以下正則表達(dá)式，它似乎正確標(biāo)記化，但我不確定如何(如果可能)使用 regex_replace 執(zhí)行條件替換.

What I want to do is replace all ' ' with '_' and all other non letter or number characters with an empty string. I have the following regex created and it seems to tokenize correctly, but I am not sure how to (if possible) perform a conditional replace using regex_replace.

string test = "test replacing "these characters"";
regex reg("(\s+)|(\W+)");

替換后的預(yù)期結(jié)果是:

string result = "test_replacing_these_characters";

我不能使用 boost，這就是為什么我把它排除在標(biāo)簽之外.所以請(qǐng)不要回答包括提升.我必須用標(biāo)準(zhǔn)庫來做到這一點(diǎn).可能是不同的正則表達(dá)式可以實(shí)現(xiàn)目標(biāo)，或者我只是堅(jiān)持做兩次.

I cannot use boost, which is why I left it out of the tags. So please no answer that includes boost. I have to do this with the standard library. It may be that a different regex would accomplish the goal or that I am just stuck doing two passes.

我不記得在我原來的正則表達(dá)式時(shí) w 中包含了哪些字符，在查找之后我進(jìn)一步簡化了表達(dá)式.同樣，目標(biāo)是任何匹配 s+ 的內(nèi)容都應(yīng)替換為 '_'，任何匹配的 W+ 均應(yīng)替換為空字符串.

I did not remember what characters were included in w at the time of my original regex, after looking it up I have further simplified the expression. Again the goal is anything matching s+ should be replaced with '_' and anything matching W+ should be replaced with empty string.

推薦答案

C++ (0x, 11, tr1) 正則表達(dá)式 不要在每種情況下都確實(shí)有效(stackoverflow)(查找 此頁面 上的短語 regex 用于 gcc)，因此最好使用 boost 一段時(shí)間.

The c++ (0x, 11, tr1) regular expressions do not really work (stackoverflow) in every case (look up the phrase regex on this page for gcc), so it is better to use boost for a while.

你可以試試你的編譯器是否支持所需的正則表達(dá)式:

You may try if your compiler supports the regular expressions needed:

#include <string>
#include <iostream>
#include <regex>

using namespace std;

int main(int argc, char * argv[]) {
    string test = "test replacing "these characters"";
    regex reg("[^\w]+");
    test = regex_replace(test, reg, "_");
    cout << test << endl;
}

以上適用于 Visual Studio 2012Rc.

The above works in Visual Studio 2012Rc.

編輯 1:要在一次傳遞中替換兩個(gè)不同的字符串(取決于匹配)，我認(rèn)為這在這里不起作用.在 Perl 中，這可以在計(jì)算的替換表達(dá)式(/e 開關(guān))中輕松完成.

Edit 1: To replace by two different strings in one pass (depending on the match), I'd think this won't work here. In Perl, this could easily be done within evaluated replacement expressions (/e switch).

因此，正如您已經(jīng)懷疑的那樣，您需要兩次通過:

Therefore, you'll need two passes, as you already suspected:

 ...
 string test = "test replacing "these characters"";
 test = regex_replace(test, regex("\s+"), "_");
 test = regex_replace(test, regex("\W+"), "");
 ...

編輯 2:

如果可以在 regex_replace 中使用 回調(diào)函數(shù) tr()，那么您可以修改那里的替換，例如:

If it would be possible to use a callback function tr() in regex_replace, then you could modify the substitution there, like:

 string output = regex_replace(test, regex("\s+|\W+"), tr);

用 tr() 做替換工作:

 string tr(const smatch &m) { return m[0].str()[0] == ' ' ? "_" : ""; }

問題就解決了.不幸的是，在某些 C++11 正則表達(dá)式實(shí)現(xiàn)中沒有這樣的重載，但是 Boost 有一個(gè).以下將與 boost 一起使用并使用一次傳遞:

the problem would have been solved. Unfortunately, there's no such overload in some C++11 regex implementations, but Boost has one. The following would work with boost and use one pass:

...
#include <boost/regex.hpp>
using namespace boost;
...
string tr(const smatch &m) { return m[0].str()[0] == ' ' ? "_" : ""; }
...

string test = "test replacing "these characters"";
test = regex_replace(test, regex("\s+|\W+"), tr);   // <= works in Boost
...

也許有一天這將適用于 C++11 或接下來的任何數(shù)字.

Maybe some day this will work with C++11 or whatever number comes next.

問候

rbo

這篇關(guān)于有條件地替換字符串中的正則表達(dá)式匹配項(xiàng)的文章就介紹到這了，希望我們推薦的答案對(duì)大家有所幫助，也希望大家多多支持html5模板網(wǎng)！