C++删除标点符号前的所有空格，如果标点符号后不存在则添加空格

Question

C++ problem - I need to :

• remove all the spaces that come before punctuation signs in a string
• add spaces if none exist after punctuation signs. I've found a partial solution using regex which solves the first part of the problem,

I would appreciate an explanation of how it works and any ideas on how I could modify it to cover the second part of the problem as well. There are no limitations except I'm not looking for any solutions based on hardcoded strings

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;
}

Input example : I would ,if at all possible , like to write this sentence properly .

Desired outcome : I would, if at all possible, like to write this sentence properly.

Answer 1

Your example matches "one or more spaces" that is followed by period or comma (without matching the period or comma), and replaced those spaces with nothing.

This modifies is so the regex matches "any number of spaces, dot or comma, any number of spaces", and replaces the entire match with the dot or comma ($1 refers to the part of the pattern in parens) followed by one space.

std::string fix_string(const std::string& str) {
    static const std::regex rgx_pattern("\\s*([.,])\\s*");
    std::string rtn;
    rtn.reserve(str.size());
    std::regex_replace(std::back_insert_iterator<std::string>(rtn), str.cbegin(), str.cend(), rgx_pattern, "$1 ");
    return rtn;
}