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<body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"><div class="article">
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<div><h1 class="title">
<a name="id2702654"></a>libxslt Tutorial</h1></div>
<div><h3 class="author">John Fleck</h3></div>
<div><p class="releaseinfo">
This is version 0.4 of the libxslt Tutorial
</p></div>
<div><p class="copyright">Copyright � 2001 John Fleck</p></div>
<div><div class="legalnotice"><p>Permission is granted to copy, distribute and/or modify this
document under the terms of the <i>GNU Free Documentation
License</i>, 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 <a href="http://www.gnu.org/copyleft/fdl.html" target="_top">here</a>.</p></div></div>
<hr>
</div>
<div class="toc">
<p><b>Table of Contents</b></p>
<dl>
<dt> <a href="#introduction">Introduction</a>
</dt>
<dt> <a href="#functions">Primary Functions</a>
</dt>
<dd><dl>
<dt> <a href="#preparing">Preparing to Parse</a>
</dt>
<dt> <a href="#parsethestylesheet">Parse the Stylesheet</a>
</dt>
<dt> <a href="#parseinputfile">Parse the Input File</a>
</dt>
<dt> <a href="#applyingstylesheet">Applying the Stylesheet</a>
</dt>
<dt> <a href="#saveresult">Saving the result</a>
</dt>
<dt> <a href="#parameters">Parameters</a>
</dt>
<dt> <a href="#cleanup">Cleanup</a>
</dt>
</dl></dd>
<dt>A <a href="#thecode">The Code</a>
</dt>
</dl>
</div>
<div class="abstract">
<p>
<a name="id2705766"></a><b>Abstract</b>
</p>
<p>A tutorial on building a simple application using the
libxslt library to perform
XSLT transformations to convert an
XML file into HTML.</p>
</div>
<div class="sect1">
<a name="introduction"></a><div class="titlepage"><div><h2 class="title" style="clear: both">
<a name="introduction"></a>Introduction</h2></div></div>
<p>The Extensible Markup Language (XML) 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 XML files.
</p>
<p>One of the most important of those tools is XSLT:
Extensible Stylesheet Language Transformations. XSLT
is a declarative language that allows you to
translate your XML into arbitrary text output
using a stylesheet. libxslt provides the
functions to perform the transformation.
</p>
<p>libxslt is a free C language library
written by Daniel Veillard for the GNOME project
allowing you to write programs that perform XSLT
transformations.
<div class="note" style="margin-left: 0.5in; margin-right: 0.5in;">
<h3 class="title">
<a name="id2754803"></a>Note</h3>
<p>
While libxslt was written
under the auspices of the GNOME project, it does not
depend on any GNOME libraries. None are used in the
example in this tutorial.
</p>
</div>
</p>
<p>This tutorial illustrates a simple program that reads an
XML file, applies a stylesheet and saves the resulting
output. This is not a program you would want to create
yourself. xsltproc, which is included with the
libxslt package, does the same thing and is
more robust and full-featured. The program written for this tutorial is a
stripped-down version of xsltproc designed to
illustrate the functionality of libxslt.
</p>
<p>The full code for xsltproc is in
<tt>xsltproc.c</tt> in the libxslt
distribution. It also is available <a href="http://cvs.gnome.org/lxr/source/libxslt/libxslt/xsltproc.c" target="_top">on the
web</a>.
</p>
<p>References:
<div class="itemizedlist"><ul>
<li><p>
<a name="id2708005"></a><a href="http://www.w3.org/XML/" target="_top">W3C XML page</a>
</p></li>
<li><p>
<a name="id2708026"></a><a href="http://www.w3.org/Style/XSL/" target="_top">W3C
XSL page.</a>
</p></li>
<li><p>
<a name="id2708047"></a><a href="http://xmlsoft.org/XSLT/" target="_top">libxslt</a>
</p></li>
</ul></div>
</p>
</div>
<div class="sect1">
<a name="functions"></a><div class="titlepage"><div><h2 class="title" style="clear: both">
<a name="functions"></a>Primary Functions</h2></div></div>
<div class="toc">
<p><b>Table of Contents</b></p>
<dl>
<dt> <a href="#preparing">Preparing to Parse</a>
</dt>
<dt> <a href="#parsethestylesheet">Parse the Stylesheet</a>
</dt>
<dt> <a href="#parseinputfile">Parse the Input File</a>
</dt>
<dt> <a href="#applyingstylesheet">Applying the Stylesheet</a>
</dt>
<dt> <a href="#saveresult">Saving the result</a>
</dt>
<dt> <a href="#parameters">Parameters</a>
</dt>
<dt> <a href="#cleanup">Cleanup</a>
</dt>
</dl>
</div>
<p>To transform an XML file, you must perform three
functions:
<div class="orderedlist"><ol type="1">
<li><p>
<a name="id2708093"></a>parse the input file</p></li>
<li><p>
<a name="id2708101"></a>parse the stylesheet</p></li>
<li><p>
<a name="id2708110"></a>apply the stylesheet</p></li>
</ol></div>
</p>
<div class="sect2">
<a name="preparing"></a><div class="titlepage"><div><h3 class="title">
<a name="preparing"></a>Preparing to Parse</h3></div></div>
<p>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 libxslt. Any
libxml2 program that parses
XML files would need to take similar steps.
</p>
<p>First, you need set up some libxml
housekeeping. Pass the integer value <i><tt>1</tt></i> to the
<tt>xmlSubstituteEntitiesDefault</tt> function, which tells
the libxml2 parser to substitute entities as
it parses your file. (Passing <i><tt>0</tt></i> causes
libxml2 to not perform entity substitution.)
</p>
<p>Second, set <tt>xmlLoadExtDtdDefaultValue</tt> equal to
<i><tt>1</tt></i>. This tells libxml
to load external entity subsets. If you do not do this and your
input file includes entities through external subsets, you will get
errors.</p>
</div>
<div class="sect2">
<a name="parsethestylesheet"></a><div class="titlepage"><div><h3 class="title">
<a name="parsethestylesheet"></a>Parse the Stylesheet</h3></div></div>
<p>Parsing the stylesheet takes a single function call, which takes a
variable of type xmlChar:
<pre class="programlisting">
<tt>cur</tt> = xsltParseStylesheetFile((const xmlChar *)argv[i]);
</pre>
In this case, I cast the stylesheet file name, passed in as a
command line argument, to <i>xmlChar</i>. The return value
is of type <i>xsltStylesheetPtr</i>, 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.
</p>
</div>
<div class="sect2">
<a name="parseinputfile"></a><div class="titlepage"><div><h3 class="title">
<a name="parseinputfile"></a>Parse the Input File</h3></div></div>
<p>Parsing the input file takes a single function call:
<pre class="programlisting">
doc = xmlParseFile(argv[i]);
</pre>
It returns an <i>xmlDocPtr</i>, a struct in memory that
contains the document tree. It can be manipulated directly, but for this
example you will not need to.
</p>
</div>
<div class="sect2">
<a name="applyingstylesheet"></a><div class="titlepage"><div><h3 class="title">
<a name="applyingstylesheet"></a>Applying the Stylesheet</h3></div></div>
<p>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 <tt>xsltApplyStylesheet</tt>:
<pre class="programlisting">
res = xsltApplyStylesheet(cur, doc, params);
</pre>
The function takes an xsltStylesheetPtr and an
xmlDocPtr, the values returned by the previous two functions. The third
variable, <tt>params</tt> can be used to pass
XSLT parameters to the stylesheet. It is a
NULL-terminated array of name/value pairs of const char's.
</p>
</div>
<div class="sect2">
<a name="saveresult"></a><div class="titlepage"><div><h3 class="title">
<a name="saveresult"></a>Saving the result</h3></div></div>
<p>libxslt includes a family of functions to use in
saving the resulting output. For this example,
<tt>xsltSaveResultToFile</tt> is used, and the results are
saved to stdout:
<pre class="programlisting">
xsltSaveResultToFile(stdout, res, cur);
</pre>
<div class="note" style="margin-left: 0.5in; margin-right: 0.5in;">
<h3 class="title">
<a name="id2708587"></a>Note</h3>
<p>libxml also contains output
functions, such as <tt>xmlSaveFile</tt>, which can be
used here. However, output-related information contained in the
stylesheet, such as a declaration of the encoding to be used, will
be lost if one of the libxslt save
functions is not used.</p>
</div>
</p>
</div>
<div class="sect2">
<a name="parameters"></a><div class="titlepage"><div><h3 class="title">
<a name="parameters"></a>Parameters</h3></div></div>
<p>
In XSLT, parameters may be used as a way to pass
additional information to a
stylesheet. libxslt accepts
XSLT parameters as one of the values passed to
<tt>xsltApplyStylesheet</tt>.
</p>
<p>
In the tutorial example and in xsltproc,
on which the tutorial example is based, parameters to be passed take the
form of key-value pairs. The program collects them from command line
arguments, inserting them in the array <tt>params</tt>, then
passes them to the function. The final element in the array is set to
<i><tt>NULL</tt></i>.
<div class="note" style="margin-left: 0.5in; margin-right: 0.5in;">
<h3 class="title">
<a name="id2708668"></a>Note</h3>
<p>
If a parameter being passed is a string rather than an
XSLT node, it must be escaped. For the tutorial
program, that would be done as follows:
<b>tutorial]$ ./libxslt_tutorial --param rootid "'asect1'"
stylesheet.xsl filename.xml</b>
</p>
</div>
</p>
</div>
<div class="sect2">
<a name="cleanup"></a><div class="titlepage"><div><h3 class="title">
<a name="cleanup"></a>Cleanup</h3></div></div>
<p>After you are finished, libxslt and
libxml provide functions for deallocating
memory.
</p>
<p>
<pre class="programlisting">
xsltFreeStylesheet(cur);<a name="cleanupstylesheet"></a><img src="../images/callouts/1.png" alt="1" border="0">
xmlFreeDoc(res);<a name="cleanupresults"></a><img src="../images/callouts/2.png" alt="2" border="0">
xmlFreeDoc(doc);<a name="cleanupdoc"></a><img src="../images/callouts/3.png" alt="3" border="0">
xsltCleanupGlobals();<a name="cleanupglobals"></a><img src="../images/callouts/4.png" alt="4" border="0">
xmlCleanupParser();<a name="cleanupparser"></a><img src="../images/callouts/5.png" alt="5" border="0">
</pre>
<div class="calloutlist">
<a name="id2708994"></a><table border="0" summary="Callout list">
<tr>
<td width="5%" valign="top" align="left">
<a name="id2709000"></a><a href="#cleanupstylesheet"><img src="../images/callouts/1.png" alt="1" border="0"></a> </td>
<td valign="top" align="left"><p>Free the memory used by your stylesheet.</p></td>
</tr>
<tr>
<td width="5%" valign="top" align="left">
<a name="id2709117"></a><a href="#cleanupresults"><img src="../images/callouts/2.png" alt="2" border="0"></a> </td>
<td valign="top" align="left"><p>Free the memory used by the results document.</p></td>
</tr>
<tr>
<td width="5%" valign="top" align="left">
<a name="id2709136"></a><a href="#cleanupdoc"><img src="../images/callouts/3.png" alt="3" border="0"></a> </td>
<td valign="top" align="left"><p>Free the memory used by your original document.</p></td>
</tr>
<tr>
<td width="5%" valign="top" align="left">
<a name="id2709155"></a><a href="#cleanupglobals"><img src="../images/callouts/4.png" alt="4" border="0"></a> </td>
<td valign="top" align="left"><p>Free memory used by libxslt global
variables</p></td>
</tr>
<tr>
<td width="5%" valign="top" align="left">
<a name="id2709176"></a><a href="#cleanupparser"><img src="../images/callouts/5.png" alt="5" border="0"></a> </td>
<td valign="top" align="left"><p>Free memory used by the XML parser</p></td>
</tr>
</table>
</div>
</p>
</div>
</div>
<div class="appendix">
<h2 class="title" style="clear: both">
<a name="thecode"></a>A. The Code</h2>
<p>
<tt>libxslt_tutorial.c</tt>
<pre class="programlisting">
/*
* libxslt_tutorial.c: demo program for the XSL Transformation 1.0 engine
*
* based on xsltproc.c, by Daniel.Veillard@imag.fr
* by John Fleck
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; either version 2 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, write to the Free Software
* Foundation, Inc., 59 Temple Place - Suite 330, Cambridge, MA 02139, USA.
*
*/
#include <string.h>
#include <libxml/xmlmemory.h>
#include <libxml/debugXML.h>
#include <libxml/HTMLtree.h>
#include <libxml/xmlIO.h>
#include <libxml/DOCBparser.h>
#include <libxml/xinclude.h>
#include <libxml/catalog.h>
#include <libxslt/xslt.h>
#include <libxslt/xsltInternals.h>
#include <libxslt/transform.h>
#include <libxslt/xsltutils.h>
extern int xmlLoadExtDtdDefaultValue;
static void usage(const char *name) {
printf("Usage: %s [options] stylesheet file [file ...]\n", name);
printf(" --param name value : pass a (parameter,value) pair\n");
}
int
main(int argc, char **argv) {
int i;
const char *params[16 + 1];
int nbparams = 0;
xsltStylesheetPtr cur = NULL;
xmlDocPtr doc, res;
if (argc <= 1) {
usage(argv[0]);
return(1);
}
for (i = 1; i < argc; i++) {
if (argv[i][0] != '-')
break;
if ((!strcmp(argv[i], "-param")) ||
(!strcmp(argv[i], "--param"))) {
i++;
params[nbparams++] = argv[i++];
params[nbparams++] = argv[i];
if (nbparams >= 16) {
fprintf(stderr, "too many params\n");
return (1);
}
} else {
fprintf(stderr, "Unknown option %s\n", argv[i]);
usage(argv[0]);
return (1);
}
}
params[nbparams] = NULL;
xmlSubstituteEntitiesDefault(1);
xmlLoadExtDtdDefaultValue = 1;
cur = xsltParseStylesheetFile((const xmlChar *)argv[i]);
i++;
doc = xmlParseFile(argv[i]);
res = xsltApplyStylesheet(cur, doc, params);
xsltSaveResultToFile(stdout, res, cur);
xsltFreeStylesheet(cur);
xmlFreeDoc(res);
xmlFreeDoc(doc);
xsltCleanupGlobals();
xmlCleanupParser();
return(0);
}
</pre>
</p>
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