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- [/
- / 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]
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