#include <iostream>
#include <string>
#include <regex>
#include <iterator>
 
std::string fix_string(const std::string& str) {
  static const std::regex rgx_pattern("\\s+(?=[\\.,])");
  std::string rtn;
  rtn.reserve(str.size());
  std::regex_replace(std::back_insert_iterator<std::string>(rtn),
                     str.cbegin(),
                     str.cend(),
                     rgx_pattern,
                     "");
  return rtn;
}
 
int main(int argc, char *argv[]) {
  std::string str = "This  , is a string   . And another .";
  std::string new_str = fix_string(str);
 
  std::cout << "Old String: " << str << "\n";
  std::cout << "Fixed String: " << new_str << std::endl;
 
  return 0;
}
 

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