In order to search for occurrences of a regular expression through a string you should perform the following:

1. Include headers <regex> and <string> and the namespace std::string_literals for C++14 standard user-defined literals for strings:

        #include <regex> 
        #include <string> 
        using namespace std::string_literals;

2. Use raw string literals to specify the regular expression to avoid escaping backslashes (that can occur frequently). The following regular expression validates the file format proposed earlier:

        auto pattern {R"(^(?!#)(w+)s*=s*([wd]+[wd._,-:]*)$)"s};

3. Create an std::regex/std::wregex object (depending on the character set that is used) to encapsulate the regular expression:

        auto rx = std::regex{pattern};

4. To search for the first occurrence of a regular expression in a given text, use the general purpose algorithm std::regex_search() (example 1):

        auto match = std::smatch{}; 
        if (std::regex_search(text, match, rx)) 
        { 
          std::cout << match[1] << '=' << match[2] << std::endl; 
        }

5. To find all the occurrences of a regular expression in a given text, use the iterator std::regex_iterator (example 2):

        auto end = std::sregex_iterator{}; 
        for (auto it=std::sregex_iterator{ std::begin(text),  
                                           std::end(text), rx }; 
             it != end; ++it) 
        { 
          std::cout << ''' << (*it)[1] << "'='"  
                    << (*it)[2] << ''' << std::endl; 
        }

6. To iterate through all the subexpressions of a match, use the iterator std::regex_token_iterator (example 3):

        auto end = std::sregex_token_iterator{}; 
        for (auto it = std::sregex_token_iterator{ 
                          std::begin(text),  std::end(text), rx }; 
             it != end; ++it) 
        { 
          std::cout << *it << std::endl; 
        }