std::regex_replace to replace multiple combinations

I am trying to utilize the std::regex_replace to replace a few combinations of characters with other characters. However, each set of characters has a different set of characters I would like to replace it with (it depends on the character).

I thought about using a map , but that will not work as I do not have access to the character being replaced (as seen in the code). Any idea how to cover all replacement cases in one regex_replace statement (or perhaps a better approach) ?

Current Code:

std::regex r(" c|ph|th|ea|c|w");
    map<string, string> comb{
        {" c", "k"},
        { "ph", "f" },  
        { "th", "z" },
        { "ea", "e" },
        { "c", "s" },
        { "w", "v" }
    };
line = std::regex_replace(line, r, comb[r]);

We can hack together our own custom regex_replace using a regex_iterator and your map:

Live Demo

First, let's write function that accepts a std::map<string, string> and returns a regex that is just an alternation | between the keys. This will let us keep a strong association between the map and the resulting regex.

std::regex regex_from_map(const std::map<std::string, std::string>& map)
{
    std::string pattern_str = "(";
    auto it = map.begin();
    if (it != map.end())
    {
        pattern_str += it->first;
        for(++it; it != map.end(); ++it)
            pattern_str += "|" + it->first;
    }
    pattern_str += ")";
    return std::regex(pattern_str);
}

Next, let's write a function that accepts the text to be matched and your replacement map, then iterates over each match and finds the appropriate replacement to build the result string:

std::string custom_regex_replace(const std::string& text,
    const std::map<std::string, std::string>& replacement_map)
{
    auto regex = regex_from_map(replacement_map);
    std::string result;
    std::sregex_iterator it(text.begin(), text.end(), regex);
    std::sregex_iterator end;

    size_t last_pos = 0;
    for (; it != end; ++it) {
        result += text.substr(last_pos, it->position() - last_pos);
        result += replacement_map.at(it->str());
        last_pos = it->position() + it->length();
    }
    result += text.substr(last_pos, text.size() - last_pos);

    return result;
}

Finally, calling our custom replacement function:

int main() {
    std::map<std::string, std::string> replacement_map = 
    {   {" c", "k"},
        { "ph", "f" },  
        { "th", "z" },
        { "ea", "e" },
        { "c", "s" },
        { "w", "v" }
    };

    std::string text = "each word pheels new, cnow?";
    std::string new_text = custom_regex_replace(text, replacement_map);
    std::cout << new_text << std::endl;

    return 0;
}

Input:

"each word pheels new, cnow?"

Output:

"esh vord feels nev,knov?"

(Note that " c" is replace with "k", so the space after the comma was deleted)