| [/ |
| / Copyright (c) 2008 Eric Niebler |
| / |
| / 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 Dynamic Regexes] |
| |
| [h2 Overview] |
| |
| Static regexes are dandy, but sometimes you need something a bit more ... dynamic. Imagine you are developing |
| a text editor with a regex search/replace feature. You need to accept a regular expression from the end user |
| as input at run-time. There should be a way to parse a string into a regular expression. That's what xpressive's |
| dynamic regexes are for. They are built from the same core components as their static counterparts, but they |
| are late-bound so you can specify them at run-time. |
| |
| [h2 Construction and Assignment] |
| |
| There are two ways to create a dynamic regex: with the _regex_compile_ |
| function or with the _regex_compiler_ class template. Use _regex_compile_ |
| if you want the default locale. Use _regex_compiler_ if you need to |
| specify a different locale. In the section on |
| [link boost_xpressive.user_s_guide.grammars_and_nested_matches regex grammars], |
| we'll see another use for _regex_compiler_. |
| |
| Here is an example of using `basic_regex<>::compile()`: |
| |
| sregex re = sregex::compile( "this|that", regex_constants::icase ); |
| |
| Here is the same example using _regex_compiler_: |
| |
| sregex_compiler compiler; |
| sregex re = compiler.compile( "this|that", regex_constants::icase ); |
| |
| _regex_compile_ is implemented in terms of _regex_compiler_. |
| |
| [h2 Dynamic xpressive Syntax] |
| |
| Since the dynamic syntax is not constrained by the rules for valid C++ expressions, we are free to use familiar |
| syntax for dynamic regexes. For this reason, the syntax used by xpressive for dynamic regexes follows the |
| lead set by John Maddock's [@http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2003/n1429.htm proposal] |
| to add regular expressions to the Standard Library. It is essentially the syntax standardized by |
| [@http://www.ecma-international.org/publications/files/ECMA-ST/Ecma-262.pdf ECMAScript], with minor changes |
| in support of internationalization. |
| |
| Since the syntax is documented exhaustively elsewhere, I will simply refer you to the existing standards, rather |
| than duplicate the specification here. |
| |
| [h2 Internationalization] |
| |
| As with static regexes, dynamic regexes support internationalization by allowing you to specify a different |
| `std::locale`. To do this, you must use _regex_compiler_. The _regex_compiler_ class has an `imbue()` function. |
| After you have imbued a _regex_compiler_ object with a custom `std::locale`, all regex objects compiled by |
| that _regex_compiler_ will use that locale. For example: |
| |
| std::locale my_locale = /* initialize your locale object here */; |
| sregex_compiler compiler; |
| compiler.imbue( my_locale ); |
| sregex re = compiler.compile( "\\w+|\\d+" ); |
| |
| This regex will use `my_locale` when evaluating the intrinsic character sets `"\\w"` and `"\\d"`. |
| |
| [endsect] |