std::regex_replace

 

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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>& str, 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>& str, 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 the regular expression re to perform substitution on the target character sequence:

1,2) Copies characters in the range [first, last) to out, replacing any sequences that match re with characters formatted by fmt. Equivalent to:

using iter_type = std::regex_iterator<BidirIt, CharT, Traits>;
iter_type seq_begin(first, last, re, flags), seq_end;

using result_type = std::match_results<BidirIt>;
result_type m;

bool need_to_copy = (flags & std::regex_constants::format_no_copy) == 0;
bool format_all = (flags & std::regex_constants::format_first_only) != 0;

for (iter_type i = seq_begin; i != seq.end(); ++i)
{
    m = *i;
    if (need_to_copy)
        out = std::copy(m.prefix().first, m.prefix().second, out);
    if (format_all || i == seq_begin)
        out = /* replace-expr */
}

if (need_to_copy)
    out = m.ready()
              ? std::copy(m.suffix().first, m.suffix().second, out)
              : std::copy(first, last, out);

return out;

1) The expression /* replace-expr */ is m.format(out, fmt, flags).

2) The expression /* replace-expr */ is m.format(out, fmt, fmt + std::char_traits<CharT>::length(fmt), flags).

3,4) Equivalent to std::basic_string<CharT, STraits, SAlloc> result;
regex_replace(std::back_inserter(result),
str.begin(), str.end(), re, fmt, flags);
return result;.

5,6) Equivalent to std::basic_string<CharT, STraits, SAlloc> result;
regex_replace(std::back_inserter(result),
s, s + std::char_traits<CharT>::length(s), re, fmt, flags);
return result;.

Parameters

first, last	-	the target character range
str	-	the target std::string
s	-	the target null-terminated C-style string
re	-	the regular expression
fmt	-	the regex replacement format string, exact syntax depends on the value of flags
flags	-	flags used to determine how the match will be performed
out	-	output iterator to store the result of the replacement

Return value

As described above.

Exceptions

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

Example

Run this code

#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

Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

DR	Applied to	Behavior as published	Correct behavior
LWG 2213	C++11	out was not updated by the replacements	out is updated

See also

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