libxslt Tutorial
John Fleck
      This is version 0.4 of the libxslt Tutorial
    
Copyright © 2001 John Fleck
Permission is granted to copy, distribute and/or modify this
	document under the terms of the 
GNU Free Documentation
	License
, 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 
http://www.gnu.org/copyleft/fdl.htmlhere .
Table of Contents
 #introductionIntroduction  #functionsPrimary Functions  #preparingPreparing to Parse  #parsethestylesheetParse the Stylesheet  #parseinputfileParse the Input File  #applyingstylesheetApplying the Stylesheet  #saveresultSaving the result  #parametersParameters  #cleanupCleanup A #thecodeThe Code Abstract
A tutorial on building a simple application using the
      libxslt library to perform
      XSLT transformations to convert an
      XML file into HTML.
Introduction
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.
    
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.
    
libxslt is a free C language library
      written by Daniel Veillard for the GNOME project
      allowing you to write programs that perform XSLT
      transformations. 
      
Note
	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.
	
    
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. 
    
The full code for xsltproc is in
      
xsltproc.c in the libxslt
      distribution. It also is available 
http://cvs.gnome.org/lxr/source/libxslt/libxslt/xsltproc.con the
      web
.
    
References:
      
http://www.w3.org/XML/W3C XML page 
http://www.w3.org/Style/XSL/W3C
	  XSL page.
http://xmlsoft.org/XSLT/libxslt 
    
Primary Functions
Table of Contents
 #preparingPreparing to Parse  #parsethestylesheetParse the Stylesheet  #parseinputfileParse the Input File  #applyingstylesheetApplying the Stylesheet  #saveresultSaving the result  #parametersParameters  #cleanupCleanup To transform an XML file, you must perform three
    functions:
      
parse the input file
parse the stylesheet
apply the stylesheet
    
Preparing to Parse
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. 
      
First, you need set up some libxml
	housekeeping. Pass the integer value 
1 to the
	
xmlSubstituteEntitiesDefault function, which tells
	the libxml2 parser to substitute entities as
	it parses your file. (Passing 
0 causes
	libxml2 to not perform entity substitution.)
      
Second, set xmlLoadExtDtdDefaultValue equal to
	
1. 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.
Parse the Stylesheet
Parsing the stylesheet takes a single function call, which takes a
	variable of type xmlChar:
	
	  
cur = xsltParseStylesheetFile((const xmlChar *)argv[i]);
	
	In this case, I cast the stylesheet file name, passed in as a
	command line argument, to 
xmlChar. The return value
	is of type 
xsltStylesheetPtr, 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.
      
Parse the Input File
Parsing the input file takes a single function call:
	
doc = xmlParseFile(argv[i]);
	
	It returns an 
xmlDocPtr, a struct in memory that
	contains the document tree. It can be manipulated directly, but for this
	example you will not need to.
      
Applying the Stylesheet
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 
xsltApplyStylesheet:
	
res = xsltApplyStylesheet(cur, doc, params);
	
	The function takes an xsltStylesheetPtr and an
	xmlDocPtr, the values returned by the previous two functions. The third
	variable, 
params can be used to pass
	XSLT parameters to the stylesheet. It is a
	NULL-terminated array of name/value pairs of const char's.
      
Saving the result
libxslt includes a family of functions to use in
	saving the resulting output. For this example,
      
xsltSaveResultToFile is used, and the results are
      saved to stdout:
	
xsltSaveResultToFile(stdout, res, cur);
	
	
Note
libxml also contains output
	    functions, such as 
xmlSaveFile, 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.
      
Parameters
	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
	
xsltApplyStylesheet.
      
	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 
params, then
	passes them to the function. The final element in the array is set to
	
NULL.
	
Note
	    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:
	    
tutorial]$ ./libxslt_tutorial --param rootid "'asect1'"
	    stylesheet.xsl filename.xml
	  
      
Cleanup
After you are finished, libxslt and
	libxml provide functions for deallocating
      memory.
      
      
	  
	  xsltFreeStylesheet(cur);
1	  xmlFreeDoc(res);
2	  xmlFreeDoc(doc);
3	  xsltCleanupGlobals();
4	  xmlCleanupParser();
5	  
	
	  
#cleanupstylesheet1  Free the memory used by your stylesheet.
#cleanupresults2  Free the memory used by the results document.
#cleanupdoc3  Free the memory used by your original document.
#cleanupglobals4  Free memory used by libxslt global
	    variables
#cleanupparser5  Free memory used by the XML parser
      
A. The Code
libxslt_tutorial.c 
/*
 * 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);
}
    
