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std::regex_replace

Defined in header <regex> 
template< class OutputIt, class BidirIt,
          class Traits, class CharT,
          class STraits, class SAlloc >
OutputIt regex_replace( OutputIt out, BidirIt first, BidirIt last,
                        const std::basic_regex<CharT,Traits>& re,
                        const std::basic_string<CharT,STraits,SAlloc>& fmt,
                        std::regex_constants::match_flag_type flags =
                            std::regex_constants::match_default );
 (1) (since C++11) 
template< class OutputIt, class BidirIt,
          class Traits, class CharT >
OutputIt regex_replace( OutputIt out, BidirIt first, BidirIt last,
                        const std::basic_regex<CharT,Traits>& re,
                        const CharT* fmt,
                        std::regex_constants::match_flag_type flags =
                            std::regex_constants::match_default );
 (2) (since C++11) 
template< class Traits, class CharT,
          class STraits, class SAlloc,
          class FTraits, class FAlloc >
std::basic_string<CharT,STraits,SAlloc>
    regex_replace( const std::basic_string<CharT,STraits,SAlloc>& s,
                   const std::basic_regex<CharT,Traits>& re,
                   const std::basic_string<CharT,FTraits,FAlloc>& fmt,
                   std::regex_constants::match_flag_type flags =
                       std::regex_constants::match_default );
 (3) (since C++11) 
template< class Traits, class CharT,
          class STraits, class SAlloc >
std::basic_string<CharT,STraits,SAlloc>
    regex_replace( const std::basic_string<CharT,STraits,SAlloc>& s,
                   const std::basic_regex<CharT,Traits>& re,
                   const CharT* fmt,
                   std::regex_constants::match_flag_type flags =
                       std::regex_constants::match_default );
 (4) (since C++11) 
template< class Traits, class CharT,
          class STraits, class SAlloc >
std::basic_string<CharT>
    regex_replace( const CharT* s,
                   const std::basic_regex<CharT,Traits>& re,
                   const std::basic_string<CharT,STraits,SAlloc>& fmt,
                   std::regex_constants::match_flag_type flags =
                       std::regex_constants::match_default );
 (5) (since C++11) 
template< class Traits, class CharT >
std::basic_string<CharT>
    regex_replace( const CharT* s,
                   const std::basic_regex<CharT,Traits>& re,
                   const CharT* fmt,
                   std::regex_constants::match_flag_type flags =
                       std::regex_constants::match_default );
 (6) (since C++11)

regex_replace uses a regular expression to perform substitution on a sequence of characters:

1) Copies characters in the range [first, last) to out, replacing any sequences that match re with characters formatted by fmt. In other words:
  • Constructs a std::regex_iterator object i as if by std::regex_iterator<BidirIt, CharT, traits> i(first, last, re, flags), and uses it to step through every match of re within the sequence [first,last).
  • For each such match m, copies the non-matched subsequence (m.prefix()) into out as if by out = std::copy(m.prefix().first, m.prefix().second, out) and then replaces the matched subsequence with the formatted replacement string as if by calling out = m.format(out, fmt, flags).
  • When no more matches are found, copies the remaining non-matched characters to out as if by out = std::copy(last_m.suffix().first, last_m.suffix().second, out) where last_m is a copy of the last match found.
  • If there are no matches, copies the entire sequence into out as-is, by out = std::copy(first, last, out)
  • If flags contains std::regex_constants::format_no_copy, the non-matched subsequences are not copied into out.
  • If flags contains std::regex_constants::format_first_only, only the first match is replaced.
2) same as 1), but the formatted replacement is performed as if by calling out = m.format(out, fmt, fmt + char_traits<CharT>::length(fmt), flags)
3-4) Constructs an empty string result of type std::basic_string<CharT, ST, SA> and calls std::regex_replace(std::back_inserter(result), s.begin(), s.end(), re, fmt, flags).
5-6) Constructs an empty string result of type std::basic_string<CharT> and calls std::regex_replace(std::back_inserter(result), s, s + std::char_traits<CharT>::length(s), re, fmt, flags).

Parameters

first, last - the input character sequence, represented as a pair of iterators
s - the input character sequence, represented as std::basic_string or character array
re - the std::basic_regex that will be matched against the input sequence
fmt - the regex replacement format string, exact syntax depends on the value of flags
flags - the match flags of type std::regex_constants::match_flag_type
out - output iterator to store the result of the replacement
Type requirements
-OutputIt must meet the requirements of LegacyOutputIterator.
-BidirIt must meet the requirements of LegacyBidirectionalIterator.

Return value

1-2) Returns a copy of the output iterator out after all the insertions.
3-6) Returns the string result which contains the output.

Exceptions

May throw std::regex_error to indicate an error condition.

Example

#include <iostream>
#include <iterator>
#include <regex>
#include <string>
 
int main()
{
   std::string text = "Quick brown fox";
   std::regex vowel_re("a|e|i|o|u");
 
   // write the results to an output iterator
   std::regex_replace(std::ostreambuf_iterator<char>(std::cout),
                      text.begin(), text.end(), vowel_re, "*");
 
   // construct a string holding the results
   std::cout << '\n' << std::regex_replace(text, vowel_re, "[$&]") << '\n';
}

Output:

Q**ck br*wn f*x
Q[u][i]ck br[o]wn f[o]x

See also

(C++11)
 attempts to match a regular expression to any part of a character sequence
(function template)
(C++11)
 options specific to matching
(typedef)
replaces specified portion of a string
(public member function of std::basic_string<CharT,Traits,Allocator>)

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https://en.cppreference.com/w/cpp/regex/regex_replace