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| <h3 class="section">6.5 Generic Charset Conversion</h3> |
| |
| <p>The conversion functions mentioned so far in this chapter all had in |
| common that they operate on character sets that are not directly |
| specified by the functions. The multibyte encoding used is specified by |
| the currently selected locale for the <code>LC_CTYPE</code> category. The |
| wide character set is fixed by the implementation (in the case of GNU C |
| library it is always UCS-4 encoded ISO 10646<!-- /@w -->. |
| |
| <p>This has of course several problems when it comes to general character |
| conversion: |
| |
| <ul> |
| <li>For every conversion where neither the source nor the destination |
| character set is the character set of the locale for the <code>LC_CTYPE</code> |
| category, one has to change the <code>LC_CTYPE</code> locale using |
| <code>setlocale</code>. |
| |
| <p>Changing the <code>LC_TYPE</code> locale introduces major problems for the rest |
| of the programs since several more functions (e.g., the character |
| classification functions, see <a href="Classification-of-Characters.html#Classification-of-Characters">Classification of Characters</a>) use the |
| <code>LC_CTYPE</code> category. |
| |
| <li>Parallel conversions to and from different character sets are not |
| possible since the <code>LC_CTYPE</code> selection is global and shared by all |
| threads. |
| |
| <li>If neither the source nor the destination character set is the character |
| set used for <code>wchar_t</code> representation, there is at least a two-step |
| process necessary to convert a text using the functions above. One would |
| have to select the source character set as the multibyte encoding, |
| convert the text into a <code>wchar_t</code> text, select the destination |
| character set as the multibyte encoding, and convert the wide character |
| text to the multibyte (= destination) character set. |
| |
| <p>Even if this is possible (which is not guaranteed) it is a very tiring |
| work. Plus it suffers from the other two raised points even more due to |
| the steady changing of the locale. |
| </ul> |
| |
| <p>The XPG2 standard defines a completely new set of functions, which has |
| none of these limitations. They are not at all coupled to the selected |
| locales, and they have no constraints on the character sets selected for |
| source and destination. Only the set of available conversions limits |
| them. The standard does not specify that any conversion at all must be |
| available. Such availability is a measure of the quality of the |
| implementation. |
| |
| <p>In the following text first the interface to <code>iconv</code> and then the |
| conversion function, will be described. Comparisons with other |
| implementations will show what obstacles stand in the way of portable |
| applications. Finally, the implementation is described in so far as might |
| interest the advanced user who wants to extend conversion capabilities. |
| |
| <ul class="menu"> |
| <li><a accesskey="1" href="Generic-Conversion-Interface.html#Generic-Conversion-Interface">Generic Conversion Interface</a>: Generic Character Set Conversion Interface. |
| <li><a accesskey="2" href="iconv-Examples.html#iconv-Examples">iconv Examples</a>: A complete <code>iconv</code> example. |
| <li><a accesskey="3" href="Other-iconv-Implementations.html#Other-iconv-Implementations">Other iconv Implementations</a>: Some Details about other <code>iconv</code> |
| Implementations. |
| <li><a accesskey="4" href="glibc-iconv-Implementation.html#glibc-iconv-Implementation">glibc iconv Implementation</a>: The <code>iconv</code> Implementation in the GNU C |
| library. |
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