c++ - 在 C++ 中有选择地替换 std::string 中的 (") 双引号

Question

我想有选择地替换 C++ std::string 中的 (") 双引号。即我想替换字符串中所有出现的 (") 双引号 (") 双引号在字符串中的第一次和最后一次出现。

示例 - 以下代码替换 ALL 出现的 (") 双引号

std::string str = "\"Hello people \" how are you doing \" what are \" you upto \"";
str = std::regex_replace(str, std::regex("\\\""), """);

但是，我不想替换字符串的第一次和最后一次出现。

i.e. in the string i don't want to replace (") just before "Hello" & the one at the end.

std::string str = "\"Hello people \" how are you doing \" what are \" you upto \"";

Answer 1

场景 1:前导空格之后/尾随空格之前的引号

您可以使用正则表达式将字符串开头/结尾的引号连同前导/尾随空格一起捕获到第 1 组中，并匹配所有其他上下文中的引号。然后您需要为每种可能性实现自定义替换:当第 1 组匹配时，您需要将整个匹配粘贴回去，如果没有，则用 " 替换:

#include <iostream>
#include <cstdlib>
#include <string>
#include <regex>
using namespace std;
 
template<class BidirIt, class Traits, class CharT, class UnaryFunction>
std::basic_string<CharT> regex_replace(BidirIt first, BidirIt last,
    const std::basic_regex<CharT,Traits>& re, UnaryFunction f)
{
    std::basic_string<CharT> s;
 
    typename std::match_results<BidirIt>::difference_type
        positionOfLastMatch = 0;
    auto endOfLastMatch = first;
 
    auto callback = [&](const std::match_results<BidirIt>& 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);
    };
 
    std::sregex_iterator begin(first, last, re), end;
    std::for_each(begin, end, callback);
 
    s.append(endOfLastMatch, last);
 
    return s;
}
 
template<class Traits, class CharT, class UnaryFunction>
std::string regex_replace(const std::string& s,
    const std::basic_regex<CharT,Traits>& re, UnaryFunction f)
{
    return regex_replace(s.cbegin(), s.cend(), re, f);
}
 
std::string my_callback(const std::smatch& m) {
  if (m.str(1).length() % 2 == 0) {
    return "&quot;";
  } else {
    return m.str(0);
  }
}
 
int main() {
    std::string str = "\"Hello people \" how are you doing \" what are \" you upto \"";
    cout << regex_replace(str, regex("(^\\s*\"|\"\\s*$)|\""), my_callback) << endl;
 
    return 0;
}

参见 C++ demo . John Martin 的回调实现.

场景 2:字符串开头/结尾的引号

你可以使用

std::regex("(?!^)\"(?!$)")

如果 " 在开头 (^) 和 处找到，则 (?!^) 否定先行匹配失败如果 (?!$) 位于字符串的 ($) 末尾，则失败。

参见 regex demo

C++ demo :

#include <iostream>
#include <regex>
using namespace std;
 
int main() {
    std::string str = "\"Hello people \" how are you doing \" what are \" you upto \"";
    str = std::regex_replace(str, std::regex("(?!^)\"(?!$)"), "&quot;");
    std::cout << str << std::endl;
    return 0;
}

输出:"Hello people " you are you doing " what are " you up to "