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<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">
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Data encoding compatibility problems are one of the most common
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difficulties encountered by programmers new to XML in
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general and libxml in particular. Thinking
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through the design of your application in light of this issue will help
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avoid difficulties later. Internally, libxml
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stores and manipulates data in the UTF-8 format. Data used by your program
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in other formats, such as the commonly used ISO-8859-1 encoding, must be
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converted to UTF-8 before passing it to libxml
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functions. If you want your program's output in an encoding other than
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UTF-8, you also must convert it.Libxml uses
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iconv if it is available to convert
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data. Without iconv, only UTF-8, UTF-16 and
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ISO-8859-1 can be used as external formats. With
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iconv, any format can be used provided
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iconv is able to convert it to and from
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UTF-8. Currently iconv supports about 150
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different character formats with ability to convert from any to any. While
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the actual number of supported formats varies between implementations, every
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iconv implementation is almost guaranteed to
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support every format anyone has ever heard of.![[Warning]](images/warning.png) | Warning |
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A common mistake is to use different formats for the internal data |
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in different parts of one's code. The most common case is an application
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that assumes ISO-8859-1 to be the internal data format, combined with
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libxml, which assumes UTF-8 to be the
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internal data format. The result is an application that treats internal
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data differently, depending on which code section is executing. The one or
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the other part of code will then, naturally, misinterpret the data.
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This example constructs a simple document, then adds content provided
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at the command line to the document's root element and outputs the results
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to <tt class="filename">stdout</tt> in the proper encoding. For this example, we
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use ISO-8859-1 encoding. The encoding of the string input at the command
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line is converted from ISO-8859-1 to UTF-8. Full code: Appendix H, Code for Encoding Conversion ExampleThe conversion, encapsulated in the example code in the
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<tt class="function">convert</tt> function, uses
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libxml's
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<tt class="function">xmlFindCharEncodingHandler</tt> function:
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 xmlCharEncodingHandlerPtr handler;
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 size = (int)strlen(in)+1;
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out_size = size*2-1;
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out = malloc((size_t)out_size);
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…
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 handler = xmlFindCharEncodingHandler(encoding);
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…
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 handler->input(out, &out_size, in, &temp);
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…
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 xmlSaveFormatFileEnc("-", doc, encoding, 1);
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| | <tt class="varname">handler</tt> is declared as a pointer to an |
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<tt class="function">xmlCharEncodingHandler</tt> function. The <tt class="function">xmlCharEncodingHandler</tt> function needs
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to be given the size of the input and output strings, which are
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calculated here for strings <tt class="varname">in</tt> and
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<tt class="varname">out</tt>. <tt class="function">xmlFindCharEncodingHandler</tt> takes as its
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argument the data's initial encoding and searches
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libxml's built-in set of conversion
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handlers, returning a pointer to the function or NULL if none is
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found. The conversion function identified by <tt class="varname">handler</tt>
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requires as its arguments pointers to the input and output strings,
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along with the length of each. The lengths must be determined
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separately by the application. To output in a specified encoding rather than UTF-8, we use
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<tt class="function">xmlSaveFormatFileEnc</tt>, specifying the
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encoding.
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</body></html>
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