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diff --git a/libstdc++-v3/docs/html/22_locale/howto.html b/libstdc++-v3/docs/html/22_locale/howto.html new file mode 100644 index 00000000000..6c76a5cef22 --- /dev/null +++ b/libstdc++-v3/docs/html/22_locale/howto.html @@ -0,0 +1,235 @@ +<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0//EN"> +<HTML> +<HEAD> + <META HTTP-EQUIV="Content-Type" CONTENT="text/html; charset=iso-8859-1"> + <META NAME="AUTHOR" CONTENT="pme@sources.redhat.com (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++-v3 HOWTO: Chapter 22</TITLE> +<LINK REL=StyleSheet HREF="../lib3styles.css"> +<!-- $Id: howto.html,v 1.8 2000/12/03 23:47:47 jsm28 Exp $ --> +</HEAD> +<BODY> + +<H1 CLASS="centered"><A NAME="top">Chapter 22: Localization</A></H1> + +<P>Chapter 22 deals with the C++ localization facilities. +</P> + + +<!-- ####################################################### --> +<HR> +<H1>Contents</H1> +<UL> + <LI><A HREF="#1">Bjarne Stroustrup on Locales</A> + <LI><A HREF="#2">Nathan Myers on Locales</A> + <LI><A HREF="#3">class locale</A> + <LI><A HREF="#4">class codecvt</A> + <LI><A HREF="#5">class ctype</A> + <LI><A HREF="#6">Correct Transformations</A> +</UL> + +<HR> + +<!-- ####################################################### --> + +<H2><A NAME="1">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: + <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> + </P> + <P>Return <A HREF="#top">to top of page</A> or + <A HREF="../faq/index.html">to the FAQ</A>. + </P> + +<HR> +<H2><A NAME="2">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> + <P>Return <A HREF="#top">to top of page</A> or + <A HREF="../faq/index.html">to the FAQ</A>. + </P> + +<HR> +<H2><A NAME="5">class locale</A></H2> + <P> Notes made during the implementation of locales can be found + <A HREF="locale.html">here</A>. + </P> + <P>Return <A HREF="#top">to top of page</A> or + <A HREF="../faq/index.html">to the FAQ</A>. + </P> + +<HR> +<H2><A NAME="4">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: +<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++-v3 +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> + + <P>Return <A HREF="#top">to top of page</A> or + <A HREF="../faq/index.html">to the FAQ</A>. + </P> + +<HR> +<H2><A NAME="5">class ctype</A></H2> + <P> Notes made during the implementation of ctype can be found + <A HREF="ctype.html">here</A>. + </P> + <P>Return <A HREF="#top">to top of page</A> or + <A HREF="../faq/index.html">to the FAQ</A>. + </P> + +<HR> +<H2><A NAME="6">Correct Transformations</A></H2> + <!-- Jumping directly 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 + <TT> extern "Danish" int tolower (int); </TT>. + </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: + <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> + 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 <TT>toupper/tolower</TT> 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: + <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) { return std::toupper(c,loc); } + private: + std::locale const& loc; + }; + + struct Tolower + { + Tolower (std::locale const& l) : loc(l) {;} + char operator() (char c) { 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("C") ); + Tolower down ( std::locale("C") ); + + // 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> + <P>The final version of the code uses <TT>bind2nd</TT> 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> + <P>Return <A HREF="#top">to top of page</A> or + <A HREF="../faq/index.html">to the FAQ</A>. + </P> + + + + +<!-- ####################################################### --> + +<HR> +<P CLASS="fineprint"><EM> +Comments and suggestions are welcome, and may be sent to +<A HREF="mailto:pme@sources.redhat.com">Phil Edwards</A> or +<A HREF="mailto:gdr@gcc.gnu.org">Gabriel Dos Reis</A>. +<BR> $Id: howto.html,v 1.8 2000/12/03 23:47:47 jsm28 Exp $ +</EM></P> + + +</BODY> +</HTML> |