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<?xml version="1.0"?>
<!DOCTYPE article PUBLIC "-//OASIS//DTD DocBook XML V4.1.2//EN"
"http://www.oasis-open.org/docbook/xml/4.1.2/docbookx.dtd" [
<!ENTITY CODE SYSTEM "libxslt_tutorial.c">
]>
<article>
<articleinfo>
<title>libxslt Tutorial</title>
<copyright>
<year>2001</year>
<holder>John Fleck</holder>
</copyright>
<legalnotice id="legalnotice">
<para>Permission is granted to copy, distribute and/or modify this
document under the terms of the <citetitle>GNU Free Documentation
License</citetitle>, Version 1.1 or any later version
published by the Free Software Foundation with no Invariant
Sections, no Front-Cover Texts, and no Back-Cover Texts. A copy of
the license can be found <ulink type="http"
url="http://www.gnu.org/copyleft/fdl.html">here</ulink>.</para>
</legalnotice>
<author>
<firstname>John</firstname>
<surname>Fleck</surname>
</author>
<releaseinfo>
This is version 0.1 of the libxslt Tutorial
</releaseinfo>
</articleinfo>
<abstract>
<para>A tutorial on building a simple application using the
<application>libxslt</application> library to perform
<acronym>XSLT</acronym> transformations to convert an
<acronym>XML</acronym> file into <acronym>HTML</acronym>.</para>
</abstract>
<sect1 id="introduction">
<title>Introduction</title>
<para>The Extensible Markup Language (<acronym>XML</acronym>) is a World
Wide Web Consortium standard for the exchange of structured data in text
form. Its popularity stems from its universality. Any computer can
read a text file. With the proper tools, any computer can read any other
computer's <acronym>XML</acronym> files.
</para>
<para>One of the most important of those tools is <acronym>XSLT</acronym>:
Extensible Stylesheet Language Transformations. <acronym>XSLT</acronym>
is a declarative language that allows you to
translate your <acronym>XML</acronym> into arbitrary text output
using a stylesheet. <application>libxslt</application> provides the
functions to perform the transformation.
</para>
<para><application>libxslt</application> is a free C language library
written by Daniel Veillard for the <acronym>GNOME</acronym> project
allowing you to write programs that perform <acronym>XSLT</acronym>
transformations.
<note>
<para>
While <application>libxslt</application> was written
under the auspices of the <acronym>GNOME</acronym> project, it does not
depend on any <acronym>GNOME</acronym> libraries. None are used in the
example in this tutorial.
</para>
</note>
</para>
<para>This tutorial illustrates a simple program that reads an
<acronym>XML</acronym> file, applies a stylesheet and saves the resulting
output. This is not a program you would want to create
yourself. <application>xsltproc</application>, which is included with the
<application>libxslt</application> package, does the same thing and is
more robust and full-featured. The program written for this tutorial is a
stripped-down version of <application>xsltproc</application> designed to
illustrate the functionality of <application>libxslt</application>.
</para>
<para>References:
<itemizedlist>
<listitem>
<para><ulink url="http://www.w3.org/XML/">W3C <acronym>XML</acronym> page</ulink></para>
</listitem>
<listitem>
<para><ulink url="http://www.w3.org/Style/XSL/">W3C
<acronym>XSL</acronym> page.</ulink></para>
</listitem>
<listitem>
<para><ulink url="http://xmlsoft.org/XSLT/">libxslt</ulink></para>
</listitem>
</itemizedlist>
</para>
</sect1>
<sect1 id="functions">
<title>Primary Functions</title>
<para>To transform an <acronym>XML</acronym> file, you must perform three
functions:
<orderedlist>
<listitem>
<para>parse the input file</para>
</listitem>
<listitem>
<para>parse the stylesheet</para>
</listitem>
<listitem>
<para>apply the stylesheet</para>
</listitem>
</orderedlist>
</para>
<sect2 id="preparing">
<title>Preparing to Parse</title>
<para>Before you can begin parsing input files or stylesheets, there are
several steps you need to take to set up entity handling. These steps are
not unique to <application>libxslt</application>. Any
<application>libxml2</application> program that parses
<acronym>XML</acronym> files would need to take similar steps.
</para>
<para>First, you need set up some <application>libxml</application>
housekeeping. Pass the integer value <parameter>1</parameter> to the
<function>xmlSubstituteEntitiesDefault</function> function, which tells
the <application>libxml2</application> parser to substitute entities as
it parses your file. (Passing <parameter>0</parameter> causes
<application>libxml2</application> to not perform entity substitution.)
</para>
<para>Second, set <varname>xmlLoadExtDtdDefaultValue</varname> equal to
<parameter>1</parameter>. This tells <application>libxml</application>
to load external entity subsets. If you do not do this and the file your
input file includes entities through external subsets, you will get
errors.</para>
</sect2>
<sect2 id="parsethestylesheet">
<title>Parse the Stylesheet</title>
<para>Parsing the stylesheet takes a single function call, which takes a
variable of type <type>xmlChar</type>:
<programlisting>
<varname>cur</varname> = xsltParseStylesheetFile((const xmlChar *)argv[1]);
</programlisting>
In this case, I cast the stylesheet file name, passed in as a
command line argument, to <emphasis>xmlChar</emphasis>. The return value
is of type <emphasis>xsltStylesheetPtr</emphasis>, a struct in memory
that contains the stylesheet tree and other information about the
stylesheet. It can be manipulated directly, but for this example you
will not need to.
</para>
</sect2>
<sect2 id="parseinputfile">
<title>Parse the Input File</title>
<para>Parsing the input file takes a single function call:
<programlisting>
doc = xmlParseFile(argv[2]);
</programlisting>
It returns an <emphasis>xmlDocPtr</emphasis>, a struct in memory that
contains the document tree. It can be manipulated directly, but for this
example you will not need to.
</para>
</sect2>
<sect2 id="applyingstylesheet">
<title>Applying the Stylesheet</title>
<para>Now that you have trees representing the document and the stylesheet
in memory, apply the stylesheet to the document. The
function that does this is <function>xsltApplyStylesheet</function>:
<programlisting>
res = xsltApplyStylesheet(cur, doc, NULL);
</programlisting>
For parameters, the function takes an xsltStylesheetPtr and an
xmlDocPtr, the values returned by the previous two functions. The third
parameter, NULL in this case, can be used to pass parameters to the
stylesheet. It is a NULL-terminated array of name/value pairs of const
char's.
</para>
</sect2>
<sect2 id="saveresult">
<title>Saving the result</title>
<para><application>libxslt</application> includes a function to use in
saving the resulting output: <function>xsltSaveResultToFile</function>. In
this case, we save the results to stdout:
<programlisting>
xsltSaveResultToFile(stdout, res, cur);
</programlisting>
</para>
</sect2>
</sect1>
<appendix id="thecode">
<title>The Code</title>
<para><filename>libxslt_tutorial.c</filename>
<programlisting>&CODE;</programlisting>
</para>
</appendix>
</article>
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