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Showing content from https://cplusplus.github.io/LWG/issue727 below:

regex_replace() doesn't accept basic_strings with custom traits and allocators

This page is a snapshot from the LWG issues list, see the Library Active Issues List for more information and the meaning of C++11 status.

Section: 28.6.10.4 [re.alg.replace] Status: C++11 Submitter: Stephan T. Lavavej Opened: 2007-09-22 Last modified: 2016-01-28

regex_match() and regex_search() take const basic_string<charT, ST, SA>&. regex_replace() takes const basic_string<charT>&. This prevents regex_replace() from accepting basic_strings with custom traits and allocators.

Overloads of regex_replace() taking basic_string should be additionally templated on class ST, class SA and take const basic_string<charT, ST, SA>&. Consistency with regex_match() and regex_search() would place class ST, class SA as the first template arguments; compatibility with existing code using TR1 and giving explicit template arguments to regex_replace() would place class ST, class SA as the last template arguments.

[ 2009-07-17 Stephan provided wording. ]

One relevant part of the proposed resolution below suggests to add a new overload of the format member function in the match_results class template that accepts two character pointers defining the begin and end of a format range. A more general approach could have proposed a pair of iterators instead, but the used pair of char pointers reflects existing practice. If the committee strongly favors an iterator-based signature, this could be simply changed. I think that the minimum requirement should be a BidirectionalIterator, but current implementations take advantage (at least partially) of the RandomAccessIterator sub interface of the char pointers.

Suggested Resolution:

[Moved into the proposed resloution]

[ 2009-07-30 Stephan agrees with Daniel's wording. Howard places Daniel's wording in the Proposed Resolution. ]

[ 2010-01-27 Moved to Tentatively Ready after 5 positive votes on c++std-lib. ]

Change 28.6.3 [re.syn] as indicated:

// 28.11.4, function template regex_replace:
template <class OutputIterator, class BidirectionalIterator,
          class traits, class charT, class ST, class SA>
  OutputIterator
  regex_replace(OutputIterator out,
                BidirectionalIterator first, BidirectionalIterator last,
                const basic_regex<charT, traits>& e,
                const basic_string<charT, ST, SA>& fmt,
                regex_constants::match_flag_type flags =
                  regex_constants::match_default);


template <class OutputIterator, class BidirectionalIterator,
          class traits, class charT>
  OutputIterator
  regex_replace(OutputIterator out,
                BidirectionalIterator first, BidirectionalIterator last,
                const basic_regex<charT, traits>& e,
                const charT* fmt,
                regex_constants::match_flag_type flags =
                  regex_constants::match_default);


template <class traits, class charT, class ST, class SA,
          class FST, class FSA>
  basic_string<charT, ST, SA>
  regex_replace(const basic_string<charT, ST, SA>& s,
                const basic_regex<charT, traits>& e,
                const basic_string<charT, FST, FSA>& fmt,
                regex_constants::match_flag_type flags =
                  regex_constants::match_default);


template <class traits, class charT, class ST, class SA>
  basic_string<charT, ST, SA>
  regex_replace(const basic_string<charT, ST, SA>& s,
                const basic_regex<charT, traits>& e,
                const charT* fmt,
                regex_constants::match_flag_type flags =
                  regex_constants::match_default);



template <class traits, class charT, class ST, class SA>
  basic_string<charT>
  regex_replace(const charT* s,
                const basic_regex<charT, traits>& e,
                const basic_string<charT, ST, SA>& fmt,
                regex_constants::match_flag_type flags =
                  regex_constants::match_default);



template <class traits, class charT>
  basic_string<charT>
  regex_replace(const charT* s,
                const basic_regex<charT, traits>& e,
                const charT* fmt,
                regex_constants::match_flag_type flags =
                  regex_constants::match_default);

Change 28.6.9 [re.results]/3, class template match_results as indicated:

template <class OutputIter>
  OutputIter
  format(OutputIter out,
         const char_type* fmt_first, const char_type* fmt_last,
         regex_constants::match_flag_type flags =
           regex_constants::format_default) const;


template <class OutputIter, class ST, class SA>
  OutputIter
  format(OutputIter out,
         const string_typebasic_string<char_type, ST, SA>& fmt,
         regex_constants::match_flag_type flags =
           regex_constants::format_default) const;

template <class ST, class SA>
  string_typebasic_string<char_type, ST, SA>
  format(const string_typebasic_string<char_type, ST, SA>& fmt,
         regex_constants::match_flag_type flags =
           regex_constants::format_default) const;


string_type
format(const char_type* fmt,
       regex_constants::match_flag_type flags =
         regex_constants::format_default) const;

Insert at the very beginning of 28.6.9.6 [re.results.form] the following:

template <class OutputIter>
  OutputIter
  format(OutputIter out,
         const char_type* fmt_first, const char_type* fmt_last,
         regex_constants::match_flag_type flags =
           regex_constants::format_default) const;
1 Requires: The type OutputIter shall satisfy the requirements for an Output Iterator (24.3.5.4 [output.iterators]).

2 Effects: Copies the character sequence [fmt_first,fmt_last) to OutputIter out. Replaces each format specifier or escape sequence in the copied range with either the character(s) it represents or the sequence of characters within *this to which it refers. The bitmasks specified in flags determine which format specifiers and escape sequences are recognized.

3 Returns: out.

Change 28.6.9.6 [re.results.form], before p. 1 until p. 3 as indicated:

template <class OutputIter, class ST, class SA>
  OutputIter
  format(OutputIter out,
         const string_typebasic_string<char_type, ST, SA>& fmt,
         regex_constants::match_flag_type flags =
           regex_constants::format_default) const;
1 Requires: The type OutputIter shall satisfy the requirements for an Output Iterator (24.2.3).

2 Effects: Copies the character sequence [fmt.begin(),fmt.end()) to OutputIter out. Replaces each format specifier or escape sequence in fmt with either the character(s) it represents or the sequence of characters within *this to which it refers. The bitmasks specified in flags determines what format specifiers and escape sequences are recognized Equivalent to return format(out, fmt.data(), fmt.data() + fmt.size(), flags).

3 Returns: out.

Change 28.6.9.6 [re.results.form], before p. 4 until p. 4 as indicated:

template <class ST, class SA>
  string_typebasic_string<char_type, ST, SA>
  format(const string_typebasic_string<char_type, ST, SA>& fmt,
         regex_constants::match_flag_type flags =
           regex_constants::format_default) const;
Effects: Returns a copy of the string fmt. Replaces each format specifier or escape sequence in fmt with either the character(s) it represents or the sequence of characters within *this to which it refers. The bitmasks specified in flags determines what format specifiers and escape sequences are recognized. Constructs an empty string result of type basic_string<char_type, ST, SA>, and calls format(back_inserter(result), fmt, flags).

Returns: result

At the end of 28.6.9.6 [re.results.form] insert as indicated:

string_type
  format(const char_type* fmt,
         regex_constants::match_flag_type flags =
           regex_constants::format_default) const;
Effects: Constructs an empty string result of type string_type, and calls format(back_inserter(result), fmt, fmt + char_traits<char_type>::length(fmt), flags).

Returns: result

Change 28.6.10.4 [re.alg.replace] before p. 1 as indicated:

template <class OutputIterator, class BidirectionalIterator,
          class traits, class charT, class ST, class SA>
  OutputIterator
  regex_replace(OutputIterator out,
                BidirectionalIterator first, BidirectionalIterator last,
                const basic_regex<charT, traits>& e,
                const basic_string<charT, ST, SA>& fmt,
                regex_constants::match_flag_type flags =
                  regex_constants::match_default);


template <class OutputIterator, class BidirectionalIterator,
          class traits, class charT>
  OutputIterator
  regex_replace(OutputIterator out,
                BidirectionalIterator first, BidirectionalIterator last,
                const basic_regex<charT, traits>& e,
                const charT* fmt,
                regex_constants::match_flag_type flags =
                  regex_constants::match_default);

Effects: [..]. If any matches are found then, for each such match, if !(flags & regex_constants::format_no_copy) calls std::copy(m.prefix().first, m.prefix().second, out), and then calls m.format(out, fmt, flags) for the first form of the function and m.format(out, fmt, fmt + char_traits<charT>::length(fmt), flags) for the second form. [..].

Change 28.6.10.4 [re.alg.replace] before p. 3 as indicated:

template <class traits, class charT, class ST, class SA,
          class FST, class FSA>
  basic_string<charT, ST, SA>
  regex_replace(const basic_string<charT, ST, SA>& s,
                const basic_regex<charT, traits>& e,
                const basic_string<charT, FST, FSA>& fmt,
                regex_constants::match_flag_type flags =
                  regex_constants::match_default);


template <class traits, class charT, class ST, class SA>
  basic_string<charT, ST, SA>
  regex_replace(const basic_string<charT, ST, SA>& s,
                const basic_regex<charT, traits>& e,
                const charT* fmt,
                regex_constants::match_flag_type flags =
                  regex_constants::match_default);

Effects: Constructs an empty string result of type basic_string<charT , ST, SA>, calls regex_replace(back_inserter(result), s.begin(), s.end(), e, fmt, flags), and then returns result.

At the end of 28.6.10.4 [re.alg.replace] add the following new prototype description:

template <class traits, class charT, class ST, class SA>
  basic_string<charT>
  regex_replace(const charT* s,
                const basic_regex<charT, traits>& e,
                const basic_string<charT, ST, SA>& fmt,
                regex_constants::match_flag_type flags =
                  regex_constants::match_default);



template <class traits, class charT>
  basic_string<charT>
  regex_replace(const charT* s,
                const basic_regex<charT, traits>& e,
                const charT* fmt,
                regex_constants::match_flag_type flags =
                  regex_constants::match_default);

Effects: Constructs an empty string result of type basic_string<charT>, calls regex_replace(back_inserter(result), s, s + char_traits<charT>::length(s), e, fmt, flags), and then returns result.

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