Edit File: ar01s09.html
<html><head><meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1"><title>Encoding Conversion</title><meta name="generator" content="DocBook XSL Stylesheets V1.61.2"><link rel="home" href="index.html" title="Libxml Tutorial"><link rel="up" href="index.html" title="Libxml Tutorial"><link rel="previous" href="ar01s08.html" title="Retrieving Attributes"><link rel="next" href="apa.html" title="A.�Compilation"></head><body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center">Encoding Conversion</th></tr><tr><td width="20%" align="left"><a accesskey="p" href="ar01s08.html">Prev</a>�</td><th width="60%" align="center">�</th><td width="20%" align="right">�<a accesskey="n" href="apa.html">Next</a></td></tr></table><hr></div><div class="sect1" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="xmltutorialconvert"></a>Encoding Conversion</h2></div></div><div></div></div><p><a class="indexterm" name="id2587348"></a> Data encoding compatibility problems are one of the most common difficulties encountered by programmers new to <span class="acronym">XML</span> in general and <span class="application">libxml</span> in particular. Thinking through the design of your application in light of this issue will help avoid difficulties later. Internally, <span class="application">libxml</span> stores and manipulates data in the UTF-8 format. Data used by your program in other formats, such as the commonly used ISO-8859-1 encoding, must be converted to UTF-8 before passing it to <span class="application">libxml</span> functions. If you want your program's output in an encoding other than UTF-8, you also must convert it.</p><p><span class="application">Libxml</span> uses <span class="application">iconv</span> if it is available to convert data. Without <span class="application">iconv</span>, only UTF-8, UTF-16 and ISO-8859-1 can be used as external formats. With <span class="application">iconv</span>, any format can be used provided <span class="application">iconv</span> is able to convert it to and from UTF-8. Currently <span class="application">iconv</span> supports about 150 different character formats with ability to convert from any to any. While the actual number of supported formats varies between implementations, every <span class="application">iconv</span> implementation is almost guaranteed to support every format anyone has ever heard of.</p><div class="warning" style="margin-left: 0.5in; margin-right: 0.5in;"><table border="0" summary="Warning"><tr><td rowspan="2" align="center" valign="top" width="25"><img alt="[Warning]" src="images/warning.png"></td><th align="left">Warning</th></tr><tr><td colspan="2" align="left" valign="top"><p>A common mistake is to use different formats for the internal data in different parts of one's code. The most common case is an application that assumes ISO-8859-1 to be the internal data format, combined with <span class="application">libxml</span>, which assumes UTF-8 to be the internal data format. The result is an application that treats internal data differently, depending on which code section is executing. The one or the other part of code will then, naturally, misinterpret the data. </p></td></tr></table></div><p>This example constructs a simple document, then adds content provided at the command line to the document's root element and outputs the results to <tt class="filename">stdout</tt> in the proper encoding. For this example, we use ISO-8859-1 encoding. The encoding of the string input at the command line is converted from ISO-8859-1 to UTF-8. Full code: <a href="aph.html" title="H.�Code for Encoding Conversion Example">Appendix�H, <i>Code for Encoding Conversion Example</i></a></p><p>The conversion, encapsulated in the example code in the <tt class="function">convert</tt> function, uses <span class="application">libxml's</span> <tt class="function">xmlFindCharEncodingHandler</tt> function: </p><pre class="programlisting"> <a name="handlerdatatype"></a><img src="images/callouts/1.png" alt="1" border="0">xmlCharEncodingHandlerPtr handler; <a name="calcsize"></a><img src="images/callouts/2.png" alt="2" border="0">size = (int)strlen(in)+1; out_size = size*2-1; out = malloc((size_t)out_size); … <a name="findhandlerfunction"></a><img src="images/callouts/3.png" alt="3" border="0">handler = xmlFindCharEncodingHandler(encoding); … <a name="callconversionfunction"></a><img src="images/callouts/4.png" alt="4" border="0">handler->input(out, &out_size, in, &temp); … <a name="outputencoding"></a><img src="images/callouts/5.png" alt="5" border="0">xmlSaveFormatFileEnc("-", doc, encoding, 1); </pre><p> </p><div class="calloutlist"><table border="0" summary="Callout list"><tr><td width="5%" valign="top" align="left"><a href="#handlerdatatype"><img src="images/callouts/1.png" alt="1" border="0"></a> </td><td valign="top" align="left"><p><tt class="varname">handler</tt> is declared as a pointer to an <tt class="function">xmlCharEncodingHandler</tt> function.</p></td></tr><tr><td width="5%" valign="top" align="left"><a href="#calcsize"><img src="images/callouts/2.png" alt="2" border="0"></a> </td><td valign="top" align="left"><p>The <tt class="function">xmlCharEncodingHandler</tt> function needs to be given the size of the input and output strings, which are calculated here for strings <tt class="varname">in</tt> and <tt class="varname">out</tt>.</p></td></tr><tr><td width="5%" valign="top" align="left"><a href="#findhandlerfunction"><img src="images/callouts/3.png" alt="3" border="0"></a> </td><td valign="top" align="left"><p><tt class="function">xmlFindCharEncodingHandler</tt> takes as its argument the data's initial encoding and searches <span class="application">libxml's</span> built-in set of conversion handlers, returning a pointer to the function or NULL if none is found.</p></td></tr><tr><td width="5%" valign="top" align="left"><a href="#callconversionfunction"><img src="images/callouts/4.png" alt="4" border="0"></a> </td><td valign="top" align="left"><p>The conversion function identified by <tt class="varname">handler</tt> requires as its arguments pointers to the input and output strings, along with the length of each. The lengths must be determined separately by the application.</p></td></tr><tr><td width="5%" valign="top" align="left"><a href="#outputencoding"><img src="images/callouts/5.png" alt="5" border="0"></a> </td><td valign="top" align="left"><p>To output in a specified encoding rather than UTF-8, we use <tt class="function">xmlSaveFormatFileEnc</tt>, specifying the encoding.</p></td></tr></table></div><p> </p></div><div class="navfooter"><hr><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="ar01s08.html">Prev</a>�</td><td width="20%" align="center"><a accesskey="u" href="index.html">Up</a></td><td width="40%" align="right">�<a accesskey="n" href="apa.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">Retrieving Attributes�</td><td width="20%" align="center"><a accesskey="h" href="index.html">Home</a></td><td width="40%" align="right" valign="top">�A.�Compilation</td></tr></table></div></body></html>