C ++正则表达式转义标点字符，例如“。”。 [英] C++ regex escaping punctional characters like "."

问题描述

匹配。在带有 std :: tr1 :: regex 类的字符串中，我使用了一种怪异的解决方法。

Matching a "." in a string with the std::tr1::regex class makes me use a weird workaround.

为什么我需要检查 \。

Why do I need to check for "\\\\." instead of "\\."?

regex(".") // Matches everything (but "\n") as expected.
regex("\\.") // Matches everything (but "\n").
regex("\\\\.") // Matches only ".".

有人可以解释我为什么吗？这真的让我感到困扰，因为我的代码是使用 boost :: regex 类编写的，不需要这种语法。

Can someone explain me why? It's really bothering me since I had my code written using boost::regex classes, which didn't need this syntax.

编辑：抱歉， regex（ \。）似乎不匹配。

Edit2：一些代码

void parser::lex(regex& token)
{
    // Skipping whitespaces
    {
        regex ws("\\s*");
        sregex_token_iterator wit(source.begin() + pos, source.end(), ws, regex_constants::match_default), wend;
        if(wit != wend)
            pos += (*wit).length();
    }

    sregex_token_iterator it(source.begin() + pos, source.end(), token, regex_constants::match_default), end;
    if (it != end)
        temp = *it;
    else
        temp = "";
}

推荐答案

事实证明，实际问题是由于使用 sregex_token_iterator 的方式引起的。使用 match_default 意味着即使字符串之间存在不匹配项，它始终会在字符串中查找下一个匹配项（如果有）。也就是说，

As it turns out, the actual problem was due to the way sregex_token_iterator was used. Using match_default meant it was always finding the next match in the string, if any, even if there is a non-match in-between. That is,

string source = "AAA.BBB";
regex dot("\\.");
sregex_token_iterator wit(source.begin(), source.end(), dot, regex_constants::match_default);

会在点上给出匹配，而不是报告没有匹配。

would give a match at the dot, rather than reporting that there was no match.

解决方案是改用 match_continuous 。

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