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diff --git a/libstdc++-v3/doc/html/22_locale/howto.html b/libstdc++-v3/doc/html/22_locale/howto.html new file mode 100644 index 0000000..3709a6f --- /dev/null +++ b/libstdc++-v3/doc/html/22_locale/howto.html @@ -0,0 +1,240 @@ +<?xml version="1.0" encoding="ISO-8859-1"?> +<!DOCTYPE html + PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" + "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> + +<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en"> +<head> + <meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1" /> + <meta name="AUTHOR" content="pme@gcc.gnu.org (Phil Edwards)" /> + <meta name="KEYWORDS" content="HOWTO, libstdc++, GCC, g++, libg++, STL" /> + <meta name="DESCRIPTION" content="HOWTO for the libstdc++ chapter 22." /> + <meta name="GENERATOR" content="vi and eight fingers" /> + <title>libstdc++ HOWTO: Chapter 22: Localization</title> +<link rel="StyleSheet" href="../lib3styles.css" type="text/css" /> +<link rel="Start" href="../documentation.html" type="text/html" + title="GNU C++ Standard Library" /> +<link rel="Prev" href="../21_strings/howto.html" type="text/html" + title="Strings" /> +<link rel="Next" href="../23_containers/howto.html" type="text/html" + title="Containers" /> +<link rel="Bookmark" href="locale.html" type="text/html" title="class locale" /> +<link rel="Bookmark" href="codecvt.html" type="text/html" title="class codecvt" /> +<link rel="Bookmark" href="ctype.html" type="text/html" title="class ctype" /> +<link rel="Bookmark" href="messages.html" type="text/html" title="class messages" /> +<link rel="Bookmark" href="http://www.research.att.com/~bs/3rd_loc0.html" type="text/html" title="Bjarne Stroustrup on Locales" /> +<link rel="Bookmark" href="http://www.cantrip.org/locale.html" type="text/html" title="Nathan Myers on Locales" /> +<link rel="Copyright" href="../17_intro/license.html" type="text/html" /> +<link rel="Help" href="../faq/index.html" type="text/html" title="F.A.Q." /> +</head> +<body> + +<h1 class="centered"><a name="top">Chapter 22: Localization</a></h1> + +<p>Chapter 22 deals with the C++ localization facilities. +</p> +<!-- I wanted to write that sentence in something requiring an exotic font, + like Cyrllic or Kanji. Probably more work than such cuteness is worth, + but I still think it'd be funny. + --> + + +<!-- ####################################################### --> +<hr /> +<h1>Contents</h1> +<ul> + <li><a href="#1">class locale</a></li> + <li><a href="#2">class codecvt</a></li> + <li><a href="#3">class ctype</a></li> + <li><a href="#4">class messages</a></li> + <li><a href="#5">Bjarne Stroustrup on Locales</a></li> + <li><a href="#6">Nathan Myers on Locales</a></li> + <li><a href="#7">Correct Transformations</a></li> +</ul> + +<!-- ####################################################### --> + +<hr /> +<h2><a name="1">class locale</a></h2> + <p>Notes made during the implementation of locales can be found + <a href="locale.html">here</a>. + </p> + +<hr /> +<h2><a name="2">class codecvt</a></h2> + <p>Notes made during the implementation of codecvt can be found + <a href="codecvt.html">here</a>. + </p> + + <p>The following is the abstract from the implementation notes: + </p> + <blockquote> + The standard class codecvt attempts to address conversions between + different character encoding schemes. In particular, the standard + attempts to detail conversions between the implementation-defined + wide characters (hereafter referred to as wchar_t) and the standard + type char that is so beloved in classic "C" (which can + now be referred to as narrow characters.) This document attempts + to describe how the GNU libstdc++ implementation deals with the + conversion between wide and narrow characters, and also presents a + framework for dealing with the huge number of other encodings that + iconv can convert, including Unicode and UTF8. Design issues and + requirements are addressed, and examples of correct usage for both + the required specializations for wide and narrow characters and the + implementation-provided extended functionality are given. + </blockquote> + +<hr /> +<h2><a name="3">class ctype</a></h2> + <p>Notes made during the implementation of ctype can be found + <a href="ctype.html">here</a>. + </p> + +<hr /> +<h2><a name="4">class messages</a></h2> + <p>Notes made during the implementation of messages can be found + <a href="messages.html">here</a>. + </p> + +<hr /> +<h2><a name="5">Bjarne Stroustrup on Locales</a></h2> + <p>Dr. Bjarne Stroustrup has released a + <a href="http://www.research.att.com/~bs/3rd_loc0.html">pointer</a> + to Appendix D of his book, + <a href="http://www.research.att.com/~bs/3rd.html">The C++ + Programming Language (3rd Edition)</a>. It is a detailed + description of locales and how to use them. + </p> + <p>He also writes: + </p> + <blockquote><em> + Please note that I still consider this detailed description of + locales beyond the needs of most C++ programmers. It is written + with experienced programmers in mind and novices will do best to + avoid it. + </em></blockquote> + +<hr /> +<h2><a name="6">Nathan Myers on Locales</a></h2> + <p>An article entitled "The Standard C++ Locale" was + published in Dr. Dobb's Journal and can be found + <a href="http://www.cantrip.org/locale.html">here</a>. + </p> + +<hr /> +<h2><a name="7">Correct Transformations</a></h2> + <!-- Jumping directly to here from chapter 21. --> + <p>A very common question on newsgroups and mailing lists is, "How + do I do <foo> to a character string?" where <foo> is + a task such as changing all the letters to uppercase, to lowercase, + testing for digits, etc. A skilled and conscientious programmer + will follow the question with another, "And how do I make the + code portable?" + </p> + <p>(Poor innocent programmer, you have no idea the depths of trouble + you are getting yourself into. 'Twould be best for your sanity if + you dropped the whole idea and took up basket weaving instead. No? + Fine, you asked for it...) + </p> + <p>The task of changing the case of a letter or classifying a character + as numeric, graphical, etc., all depends on the cultural context of the + program at runtime. So, first you must take the portability question + into account. Once you have localized the program to a particular + natural language, only then can you perform the specific task. + Unfortunately, specializing a function for a human language is not + as simple as declaring + <code> extern "Danish" int tolower (int); </code>. + </p> + <p>The C++ code to do all this proceeds in the same way. First, a locale + is created. Then member functions of that locale are called to + perform minor tasks. Continuing the example from Chapter 21, we wish + to use the following convenience functions: + </p> + <pre> + namespace std { + template <class charT> + charT + toupper (charT c, const locale& loc) const; + template <class charT> + charT + tolower (charT c, const locale& loc) const; + }</pre> + <p> + This function extracts the appropriate "facet" from the + locale <em>loc</em> and calls the appropriate member function of that + facet, passing <em>c</em> as its argument. The resulting character + is returned. + </p> + <p>For the C/POSIX locale, the results are the same as calling the + classic C <code>toupper/tolower</code> function that was used in previous + examples. For other locales, the code should Do The Right Thing. + </p> + <p>Of course, these functions take a second argument, and the + transformation algorithm's operator argument can only take a single + parameter. So we write simple wrapper structs to handle that. + </p> + <p>The next-to-final version of the code started in Chapter 21 looks like: + </p> + <pre> + #include <iterator> // for back_inserter + #include <locale> + #include <string> + #include <algorithm> + #include <cctype> // old <ctype.h> + + struct ToUpper + { + ToUpper(std::locale const& l) : loc(l) {;} + char operator() (char c) const { return std::toupper(c,loc); } + private: + std::locale const& loc; + }; + + struct ToLower + { + ToLower(std::locale const& l) : loc(l) {;} + char operator() (char c) const { return std::tolower(c,loc); } + private: + std::locale const& loc; + }; + + int main () + { + std::string s("Some Kind Of Initial Input Goes Here"); + ToUpper up(std::locale::classic()); + ToLower down(std::locale::classic()); + + // Change everything into upper case. + std::transform(s.begin(), s.end(), s.begin(), up); + + // Change everything into lower case. + std::transform(s.begin(), s.end(), s.begin(), down); + + // Change everything back into upper case, but store the + // result in a different string. + std::string capital_s; + std::transform(s.begin(), s.end(), std::back_inserter(capital_s), up); + }</pre> + <p>The <code>ToUpper</code> and <code>ToLower</code> structs can be + generalized for other character types by making <code>operator()</code> + a member function template. + </p> + <p>The final version of the code uses <code>bind2nd</code> to eliminate + the wrapper structs, but the resulting code is tricky. I have not + shown it here because no compilers currently available to me will + handle it. + </p> + + +<!-- ####################################################### --> + +<hr /> +<p class="fineprint"><em> +See <a href="../17_intro/license.html">license.html</a> for copying conditions. +Comments and suggestions are welcome, and may be sent to +<a href="mailto:libstdc++@gcc.gnu.org">the libstdc++ mailing list</a>. +</em></p> + + +</body> +</html> |