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1 <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> 2 Data encoding compatibility problems are one of the most common 3 difficulties encountered by programmers new to <span class="acronym">XML</span> in 4 general and <span class="application">libxml</span> in particular. Thinking 5 through the design of your application in light of this issue will help 6 avoid difficulties later. Internally, <span class="application">libxml</span> 7 stores and manipulates data in the UTF-8 format. Data used by your program 8 in other formats, such as the commonly used ISO-8859-1 encoding, must be 9 converted to UTF-8 before passing it to <span class="application">libxml</span> 10 functions. If you want your program's output in an encoding other than 11 UTF-8, you also must convert it.</p><p><span class="application">Libxml</span> uses 12 <span class="application">iconv</span> if it is available to convert 13 data. Without <span class="application">iconv</span>, only UTF-8, UTF-16 and 14 ISO-8859-1 can be used as external formats. With 15 <span class="application">iconv</span>, any format can be used provided 16 <span class="application">iconv</span> is able to convert it to and from 17 UTF-8. Currently <span class="application">iconv</span> supports about 150 18 different character formats with ability to convert from any to any. While 19 the actual number of supported formats varies between implementations, every 20 <span class="application">iconv</span> implementation is almost guaranteed to 21 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 22 in different parts of one's code. The most common case is an application 23 that assumes ISO-8859-1 to be the internal data format, combined with 24 <span class="application">libxml</span>, which assumes UTF-8 to be the 25 internal data format. The result is an application that treats internal 26 data differently, depending on which code section is executing. The one or 27 the other part of code will then, naturally, misinterpret the data. 28 </p></td></tr></table></div><p>This example constructs a simple document, then adds content provided 29 at the command line to the document's root element and outputs the results 30 to <tt class="filename">stdout</tt> in the proper encoding. For this example, we 31 use ISO-8859-1 encoding. The encoding of the string input at the command 32 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 33 <tt class="function">convert</tt> function, uses 34 <span class="application">libxml's</span> 35 <tt class="function">xmlFindCharEncodingHandler</tt> function: 36 </p><pre class="programlisting"> 37 <a name="handlerdatatype"></a><img src="images/callouts/1.png" alt="1" border="0">xmlCharEncodingHandlerPtr handler; 38 <a name="calcsize"></a><img src="images/callouts/2.png" alt="2" border="0">size = (int)strlen(in)+1; 39 out_size = size*2-1; 40 out = malloc((size_t)out_size); 41 42 … 43 <a name="findhandlerfunction"></a><img src="images/callouts/3.png" alt="3" border="0">handler = xmlFindCharEncodingHandler(encoding); 44 … 45 <a name="callconversionfunction"></a><img src="images/callouts/4.png" alt="4" border="0">handler->input(out, &out_size, in, &temp); 46 … 47 <a name="outputencoding"></a><img src="images/callouts/5.png" alt="5" border="0">xmlSaveFormatFileEnc("-", doc, encoding, 1); 48 </pre><p> 49 </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 50 <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 51 to be given the size of the input and output strings, which are 52 calculated here for strings <tt class="varname">in</tt> and 53 <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 54 argument the data's initial encoding and searches 55 <span class="application">libxml's</span> built-in set of conversion 56 handlers, returning a pointer to the function or NULL if none is 57 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> 58 requires as its arguments pointers to the input and output strings, 59 along with the length of each. The lengths must be determined 60 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 61 <tt class="function">xmlSaveFormatFileEnc</tt>, specifying the 62 encoding.</p></td></tr></table></div><p> 63 </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>