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c++ - 正则表达式替换字符串中是否有与 Perl 的 \L 等效的 C++？

问题描述

在 Perl 中，我可以将字符替换为小写版本，如下所示：

my $str = "HELLO WORLD HOW ARE YOU TODAY";
$str =~ s/([AEIOU])/\L\1/g;
print $str;  # HeLLo WoRLD HoW aRe You ToDaY";

我怎样才能用 C++ 做到这一点std::regex_replace？我可以将它转换成某种模式来激活诸如此类的魔法功能吗？

（真正的搜索模式更复杂，否则我只会在没有正则表达式的情况下手动完成！）

标签： c++regexc++11

解决方案

不，没有。

最后，我将 SO 中的各种代码修改为以下内容：

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

// Regex replacement with callback.
// f should be compatible with std::string(const std::smatch&).
// Adapted from code by John Martin (CC-by-SA 3.0).
//   (https://stackoverflow.com/a/37516316/560648)
template <typename UnaryFunction>
inline std::string RegexReplace(const std::string& source, const char* const re_str, UnaryFunction f, size_t* numMatches = nullptr)
{
    try
    {
        std::string s;

        std::smatch::difference_type positionOfLastMatch = 0;
        std::string::const_iterator first = std::begin(source), last = std::end(source);
        auto endOfLastMatch = first;

        if (numMatches)
            *numMatches = 0;

        auto callback = [&](const std::smatch& match)
        {
            auto positionOfThisMatch = match.position(0);
            auto diff = positionOfThisMatch - positionOfLastMatch;

            auto startOfThisMatch = endOfLastMatch;
            std::advance(startOfThisMatch, diff);

            s.append(endOfLastMatch, startOfThisMatch);
            s.append(f(match));

            auto lengthOfMatch = match.length(0);

            positionOfLastMatch = positionOfThisMatch + lengthOfMatch;

            endOfLastMatch = startOfThisMatch;
            std::advance(endOfLastMatch, lengthOfMatch);

            if (numMatches)
                (*numMatches)++;
        };

        std::regex re{re_str};
        std::sregex_iterator begin(first, last, re), end;
        std::for_each(begin, end, callback);

        s.append(endOfLastMatch, last);
        return s;
    }
    catch (const std::regex_error&)
    {
        return "";
    }
}

int main()
{
    // Change all letters but the first to lower case, but only in
    // words starting with a vowel

    const std::string str = "HELLO WORLD HOW ARE YOU TODAY";
    auto lowercaseSecondSubmatch = [](const std::smatch& match) -> std::string
    {
        if (match.size() != 3)
            return "WTF";

        std::string result = match.str(0);

        // Lowercase the second submatch
        const auto pos = match.position(2) - match.position(0);
        const auto len = match.length(2);
        const auto start = result.begin() + pos;
        const auto end   = result.begin() + pos + len;
        std::transform(start, end, start, ::tolower);

        return result;
    };

    size_t n = 0;
    std::cout << RegexReplace(str, R"REGEX(\b([AEIOUY])([A-Z]+))REGEX", lowercaseSecondSubmatch, &n) << '\n';
    std::cout << n << " matches\n";
}

（现场演示）

它当然不是完美的，但它在紧缩中起作用。

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