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### regex_replace

    #include <boost/regex.hpp>

The algorithm `regex_replace` searches through a string finding all the matches to the regular expression: for each match it then calls `match_results<>::format` to format the string and sends the result to the output iterator. Sections of text that do not match are copied to the output unchanged only if the flags parameter does not have the flag `format_no_copy` set. If the flag `format_first_only` is set then only the first occurrence is replaced rather than all occurrences.

    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 basic_string<charT>& fmt,
                                 match_flag_type flags = match_default);

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

##### Description

    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 basic_string<charT>& fmt,
                                 match_flag_type flags = match_default);

Enumerates all the occurences of expression e in the sequence [first, last), replacing each occurence with the string that results by merging the match found with the format string fmt, and copies the resulting string to out.

If the flag `format_no_copy` is set in flags then unmatched sections of text are not copied to output.

If the flag `format_first_only` is set in flags then only the first occurence of e is replaced.

The manner in which the format string fmt is interpretted, along with the rules used for finding matches, are determined by the flags set in flags: see `match_flag_type`.

Effects: Constructs an `regex_iterator` object:

    regex_iterator<BidirectionalIterator, charT, traits, Allocator>
                                              i(first, last, e, flags),

and uses i to enumerate through all of the matches m of type `match_results` `<BidirectionalIterator>` that occur within the sequence [first, last).

If no such matches are found and

    !(flags & format_no_copy)

then calls

    std::copy(first, last, out).

Otherwise, for each match found, if

    !(flags & format_no_copy)

calls

    std::copy(m.prefix().first, m.prefix().last, out),

and then calls

    m.format(out, fmt, flags).

Finally if

    !(flags & format_no_copy)

calls

    std::copy(last_m.suffix().first, last_m,suffix().last, out)

where last_m is a copy of the last match found.

If `flags & format_first_only` is non-zero then only the first match found is replaced.

Throws: `std::runtime_error` if the complexity of matching the expression against an N character string begins to exceed O(N2), or if the program runs out of stack space while matching the expression (if Boost.Regex is configured in recursive mode), or if the matcher exhausts its permitted memory allocation (if Boost.Regex is configured in non-recursive mode).

Returns: out.

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

Effects: Constructs an object `basic_string<charT> result`, calls `regex_replace(back_inserter(result), s.begin(), s.end(), e, fmt, flags)`, and then returns `result`.

##### Examples

The following example takes C/C++ source code as input, and outputs syntax highlighted HTML code.

    #include <fstream>
    #include <sstream>
    #include <string>
    #include <iterator>
    #include <boost/regex.hpp>
    #include <fstream>
    #include <iostream>

    // purpose:
    // takes the contents of a file and transform to
    // syntax highlighted code in html format

    boost::regex e1, e2;
    extern const char* expression_text;
    extern const char* format_string;
    extern const char* pre_expression;
    extern const char* pre_format;
    extern const char* header_text;
    extern const char* footer_text;

    void load_file(std::string& s, std::istream& is)
    {
       s.erase();
       s.reserve(is.rdbuf()->in_avail());
       char c;
       while(is.get(c))
       {
          if(s.capacity() == s.size())
             s.reserve(s.capacity() * 3);
          s.append(1, c);
       }
    }

    int main(int argc, const char** argv)
    {
       try{
       e1.assign(expression_text);
       e2.assign(pre_expression);
       for(int i = 1; i < argc; ++i)
       {
          std::cout << "Processing file " << argv[i] << std::endl;
          std::ifstream fs(argv[i]);
          std::string in;
          load_file(in, fs);
          std::string out_name(std::string(argv[i]) + std::string(".htm"));
          std::ofstream os(out_name.c_str());
          os << header_text;
          // strip '<' and '>' first by outputting to a
          // temporary string stream
          std::ostringstream t(std::ios::out | std::ios::binary);
          std::ostream_iterator<char, char> oi(t);
          boost::regex_replace(oi, in.begin(), in.end(),
          e2, pre_format, boost::match_default | boost::format_all);
          // then output to final output stream
          // adding syntax highlighting:
          std::string s(t.str());
          std::ostream_iterator<char, char> out(os);
          boost::regex_replace(out, s.begin(), s.end(),
          e1, format_string, boost::match_default | boost::format_all);
          os << footer_text;
       }
       }
       catch(...)
       { return -1; }
       return 0;
    }

    extern const char* pre_expression = "(<)|(>)|(&)|\\r";
    extern const char* pre_format = "(?1&lt;)(?2&gt;)(?3&amp;)";

    const char* expression_text =
       // preprocessor directives: index 1
       "(^[[:blank:]]*#(?:[^\\\\\\n]|\\\\[^\\n[:punct:][:word:]]*[\\n[:punct:][:word:]])*)|"
       // comment: index 2
       "(//[^\\n]*|/\\*.*?\\*/)|"
       // literals: index 3
       "\\<([+-]?(?:(?:0x[[:xdigit:]]+)|(?:(?:[[:digit:]]*\\.)?[[:digit:]]+"
       "(?:[eE][+-]?[[:digit:]]+)?))u?(?:(?:int(?:8|16|32|64))|L)?)\\>|"
       // string literals: index 4
       "('(?:[^\\\\']|\\\\.)*'|\"(?:[^\\\\\"]|\\\\.)*\")|"
       // keywords: index 5
       "\\<(__asm|__cdecl|__declspec|__export|__far16|__fastcall|__fortran|__import"
       "|__pascal|__rtti|__stdcall|_asm|_cdecl|__except|_export|_far16|_fastcall"
       "|__finally|_fortran|_import|_pascal|_stdcall|__thread|__try|asm|auto|bool"
       "|break|case|catch|cdecl|char|class|const|const_cast|continue|default|delete"
       "|do|double|dynamic_cast|else|enum|explicit|extern|false|float|for|friend|goto"
       "|if|inline|int|long|mutable|namespace|new|operator|pascal|private|protected"
       "|public|register|reinterpret_cast|return|short|signed|sizeof|static|static_cast"
       "|struct|switch|template|this|throw|true|try|typedef|typeid|typename|union|unsigned"
       "|using|virtual|void|volatile|wchar_t|while)\\>"
       ;

    const char* format_string = "(?1<font color=\"#008040\">$&</font>)"
                               "(?2<I><font color=\"#000080\">$&</font></I>)"
                               "(?3<font color=\"#0000A0\">$&</font>)"
                               "(?4<font color=\"#0000FF\">$&</font>)"
                               "(?5<B>$&</B>)";

    const char* header_text =
       "<HTML>\n<HEAD>\n"
       "<TITLE>Auto-generated html formated source</TITLE>\n"
       "<META HTTP-EQUIV=\"Content-Type\" CONTENT=\"text/html; charset=windows-1252\">\n"
       "</HEAD>\n"
       "<BODY LINK=\"#0000ff\" VLINK=\"#800080\" BGCOLOR=\"#ffffff\">\n"
       "<P> </P>\n<PRE>";

    const char* footer_text = "</PRE>\n</BODY>\n\n";