| <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> | |
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