path: root/libs/regex/doc/regex_replace.qbk

[/ 
  Copyright 2006-2007 John Maddock.
  Distributed under the Boost Software License, Version 1.0.
  (See accompanying file LICENSE_1_0.txt or copy at
  http://www.boost.org/LICENSE_1_0.txt).
]


[section:regex_replace 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 Formatter>
   OutputIterator regex_replace(OutputIterator out,
                                BidirectionalIterator first,
                                BidirectionalIterator last,
                                const basic_regex<charT, traits>& e,
                                Formatter fmt,
                                match_flag_type flags = match_default);

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


[h4 Description]

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

Enumerates all the occurrences of expression /e/ in the sequence \[first, last), 
replacing each occurrence with the string that results by merging the 
match found with the format string /fmt/, and copies the resulting string to /out/. 
In the case that /fmt/ is a unary, binary or ternary function object, then the
character sequence generated by that object is copied unchanged to the output when performing
a substitution.

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 
occurrence of /e/ is replaced. 

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

[*Requires]
The type `Formatter` must be either a pointer to a null-terminated string
of type `char_type[]`, or be a container of `char_type`'s (for example
`std::basic_string<char_type>`) or be a unary, binary or ternary functor
that computes the replacement string from a function call: either 
`fmt(what)` which must return a container of `char_type`'s to be used as the
replacement text, or either `fmt(what, out)` or `fmt(what, out, flags)`, both of
which write the replacement text to `*out`, and then return the new
OutputIterator position.  In each case `what` is the [match_results] object
that represents the match found.  Note that if the formatter is a functor, then it is
['passed by value]: users that want to pass function objects with internal state
might want to use [@../../../../doc/html/ref.html Boost.Ref] to wrap the object so 
that it's passed by reference.

[*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(N[super 2]), 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 Formatter>
   basic_string<charT> regex_replace(const basic_string<charT>& s,
                                     const basic_regex<charT, traits>& e,
                                     Formatter fmt,
                                     match_flag_type flags = match_default);

[*Requires]
The type `Formatter` must be either a pointer to a null-terminated string
of type `char_type[]`, or be a container of `char_type`'s (for example
`std::basic_string<char_type>`) or be a unary, binary or ternary functor
that computes the replacement string from a function call: either 
`fmt(what)` which must return a container of `char_type`'s to be used as the
replacement text, or either `fmt(what, out)` or `fmt(what, out, flags)`, both of
which write the replacement text to `*out`, and then return the new
OutputIterator position.  In each case `what` is the [match_results] object
that represents the match found.

[*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`.

[h4 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 formatted 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";
         

[endsect]