regex_replace

template<class OutIt, class BidIt, class RXtraits, class Alloc, class Elem>
    OutIt regex_replace(OutIt out,
        BidIt first, BidIt last,
        const basic_regex<Elem, RXtraits, Alloc>& re,
        const basic_string<Elem>& fmt,
        match_flag_type flags = match_default);
template<class RXtraits, class Alloc, class Elem>
    basic_string<Elem> regex_replace(const basic_string<Elem>& str,
        const basic_regex<Elem, RXtraits, Alloc>& re,
        const basic_string<Elem>& fmt,
        match_flag_type flags = match_default);

The first function constructs a regex_iterator object iter(first, last, re, flags) and uses it to split its input range [first, last) into a series of subsequences T₀M₀T₁M₁...T_N-1M_N-1T_N, where M_n is the n^th match detected by the iterator. If no matches are found, T₀ is the entire input range and N is 0. If (flags & format_first_only) != 0 only the first match is used, T₁ is all of the input text that follows the match, and N is 1. For each i in the range [0, N), if (flags & format_no_copy) == 0 it copies the text in the range T_i to the iterator out. It then calls m.format(out, fmt, flags), where m is the match_results object returned by the iterator object iter for the subsequence M_i. Finally, if (flags & format_no_copy) == 0 it copies the text in the range T_N to the iterator out. The function returns out.

The second function constructs a local variable result of type basic_string<charT> and calls regex_replace(back_inserter(result), str.begin(), str.end(), re, fmt, flags). It returns result.