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1<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN" "http://www.w3.org/TR/REC-html40/loose.dtd"> 2<html> 3<head> 4<meta content="text/html; charset=ISO-8859-1" http-equiv="Content-Type"> 5<style type="text/css"><!-- 6TD {font-size: 10pt; font-family: Verdana,Arial,Helvetica} 7BODY {font-size: 10pt; font-family: Verdana,Arial,Helvetica; margin-top: 5pt; margin-left: 0pt; margin-right: 0pt} 8H1 {font-size: 16pt; font-family: Verdana,Arial,Helvetica} 9H2 {font-size: 14pt; font-family: Verdana,Arial,Helvetica} 10H3 {font-size: 12pt; font-family: Verdana,Arial,Helvetica} 11A:link, A:visited, A:active { text-decoration: underline } 12--></style> 13<title>The parser interfaces</title> 14</head> 15<body bgcolor="#8b7765" text="#000000" link="#000000" vlink="#000000"> 16<table border="0" width="100%" cellpadding="5" cellspacing="0" align="center"><tr> 17<td width="180"> 18<a href="http://www.gnome.org/"><img src="smallfootonly.gif" alt="Gnome Logo"></a><a href="http://www.w3.org/Status"><img src="w3c.png" alt="W3C Logo"></a><a href="http://www.redhat.com/"><img src="redhat.gif" alt="Red Hat Logo"></a> 19</td> 20<td><table border="0" width="90%" cellpadding="2" cellspacing="0" align="center" bgcolor="#000000"><tr><td><table width="100%" border="0" cellspacing="1" cellpadding="3" bgcolor="#fffacd"><tr><td align="center"> 21<h1>The XML C library for Gnome</h1> 22<h2>The parser interfaces</h2> 23</td></tr></table></td></tr></table></td> 24</tr></table> 25<table border="0" cellpadding="4" cellspacing="0" width="100%" align="center"><tr><td bgcolor="#8b7765"><table border="0" cellspacing="0" cellpadding="2" width="100%"><tr> 26<td valign="top" width="200" bgcolor="#8b7765"><table border="0" cellspacing="0" cellpadding="1" width="100%" bgcolor="#000000"><tr><td> 27<table width="100%" border="0" cellspacing="1" cellpadding="3"> 28<tr><td colspan="1" bgcolor="#eecfa1" align="center"><center><b>Main Menu</b></center></td></tr> 29<tr><td bgcolor="#fffacd"><ul style="margin-left: -2pt"> 30<li><a href="index.html">Home</a></li> 31<li><a href="intro.html">Introduction</a></li> 32<li><a href="FAQ.html">FAQ</a></li> 33<li><a href="docs.html">Documentation</a></li> 34<li><a href="bugs.html">Reporting bugs and getting help</a></li> 35<li><a href="help.html">How to help</a></li> 36<li><a href="downloads.html">Downloads</a></li> 37<li><a href="news.html">News</a></li> 38<li><a href="XML.html">XML</a></li> 39<li><a href="XSLT.html">XSLT</a></li> 40<li><a href="architecture.html">libxml architecture</a></li> 41<li><a href="tree.html">The tree output</a></li> 42<li><a href="interface.html">The SAX interface</a></li> 43<li><a href="xmldtd.html">Validation & DTDs</a></li> 44<li><a href="xmlmem.html">Memory Management</a></li> 45<li><a href="encoding.html">Encodings support</a></li> 46<li><a href="xmlio.html">I/O Interfaces</a></li> 47<li><a href="catalog.html">Catalog support</a></li> 48<li><a href="library.html">The parser interfaces</a></li> 49<li><a href="entities.html">Entities or no entities</a></li> 50<li><a href="namespaces.html">Namespaces</a></li> 51<li><a href="upgrade.html">Upgrading 1.x code</a></li> 52<li><a href="threads.html">Thread safety</a></li> 53<li><a href="DOM.html">DOM Principles</a></li> 54<li><a href="example.html">A real example</a></li> 55<li><a href="contribs.html">Contributions</a></li> 56<li> 57<a href="xml.html">flat page</a>, <a href="site.xsl">stylesheet</a> 58</li> 59</ul></td></tr> 60</table> 61<table width="100%" border="0" cellspacing="1" cellpadding="3"> 62<tr><td colspan="1" bgcolor="#eecfa1" align="center"><center><b>Related links</b></center></td></tr> 63<tr><td bgcolor="#fffacd"><ul style="margin-left: -2pt"> 64<li><a href="http://mail.gnome.org/archives/xml/">Mail archive</a></li> 65<li><a href="http://xmlsoft.org/XSLT/">XSLT libxslt</a></li> 66<li><a href="http://www.cs.unibo.it/~casarini/gdome2/">DOM gdome2</a></li> 67<li><a href="ftp://xmlsoft.org/">FTP</a></li> 68<li><a href="http://www.fh-frankfurt.de/~igor/projects/libxml/">Windows binaries</a></li> 69<li><a href="http://pages.eidosnet.co.uk/~garypen/libxml/">Solaris binaries</a></li> 70<li><a href="http://bugzilla.gnome.org/buglist.cgi?product=libxml">Bug Tracker</a></li> 71</ul></td></tr> 72</table> 73</td></tr></table></td> 74<td valign="top" bgcolor="#8b7765"><table border="0" cellspacing="0" cellpadding="1" width="100%"><tr><td><table border="0" cellspacing="0" cellpadding="1" width="100%" bgcolor="#000000"><tr><td><table border="0" cellpadding="3" cellspacing="1" width="100%"><tr><td bgcolor="#fffacd"> 75<p>This section is directly intended to help programmers getting bootstrapped 76using the XML library from the C language. It is not intended to be 77extensive. I hope the automatically generated documents will provide the 78completeness required, but as a separate set of documents. The interfaces of 79the XML library are by principle low level, there is nearly zero abstraction. 80Those interested in a higher level API should <a href="#DOM">look at 81DOM</a>.</p> 82<p>The <a href="html/libxml-parser.html">parser interfaces for XML</a> are 83separated from the <a href="html/libxml-htmlparser.html">HTML parser 84interfaces</a>. Let's have a look at how the XML parser can be called:</p> 85<h3><a name="Invoking">Invoking the parser : the pull method</a></h3> 86<p>Usually, the first thing to do is to read an XML input. The parser accepts 87documents either from in-memory strings or from files. The functions are 88defined in "parser.h":</p> 89<dl> 90<dt><code>xmlDocPtr xmlParseMemory(char *buffer, int size);</code></dt> 91<dd><p>Parse a null-terminated string containing the document.</p></dd> 92</dl> 93<dl> 94<dt><code>xmlDocPtr xmlParseFile(const char *filename);</code></dt> 95<dd><p>Parse an XML document contained in a (possibly compressed) 96 file.</p></dd> 97</dl> 98<p>The parser returns a pointer to the document structure (or NULL in case of 99failure).</p> 100<h3 id="Invoking1">Invoking the parser: the push method</h3> 101<p>In order for the application to keep the control when the document is 102being fetched (which is common for GUI based programs) libxml provides a push 103interface, too, as of version 1.8.3. Here are the interface functions:</p> 104<pre>xmlParserCtxtPtr xmlCreatePushParserCtxt(xmlSAXHandlerPtr sax, 105 void *user_data, 106 const char *chunk, 107 int size, 108 const char *filename); 109int xmlParseChunk (xmlParserCtxtPtr ctxt, 110 const char *chunk, 111 int size, 112 int terminate);</pre> 113<p>and here is a simple example showing how to use the interface:</p> 114<pre> FILE *f; 115 116 f = fopen(filename, "r"); 117 if (f != NULL) { 118 int res, size = 1024; 119 char chars[1024]; 120 xmlParserCtxtPtr ctxt; 121 122 res = fread(chars, 1, 4, f); 123 if (res > 0) { 124 ctxt = xmlCreatePushParserCtxt(NULL, NULL, 125 chars, res, filename); 126 while ((res = fread(chars, 1, size, f)) > 0) { 127 xmlParseChunk(ctxt, chars, res, 0); 128 } 129 xmlParseChunk(ctxt, chars, 0, 1); 130 doc = ctxt->myDoc; 131 xmlFreeParserCtxt(ctxt); 132 } 133 }</pre> 134<p>The HTML parser embedded into libxml also has a push interface; the 135functions are just prefixed by "html" rather than "xml".</p> 136<h3 id="Invoking2">Invoking the parser: the SAX interface</h3> 137<p>The tree-building interface makes the parser memory-hungry, first loading 138the document in memory and then building the tree itself. Reading a document 139without building the tree is possible using the SAX interfaces (see SAX.h and 140<a href="http://www.daa.com.au/~james/gnome/xml-sax/xml-sax.html">James 141Henstridge's documentation</a>). Note also that the push interface can be 142limited to SAX: just use the two first arguments of 143<code>xmlCreatePushParserCtxt()</code>.</p> 144<h3><a name="Building">Building a tree from scratch</a></h3> 145<p>The other way to get an XML tree in memory is by building it. Basically 146there is a set of functions dedicated to building new elements. (These are 147also described in <libxml/tree.h>.) For example, here is a piece of 148code that produces the XML document used in the previous examples:</p> 149<pre> #include <libxml/tree.h> 150 xmlDocPtr doc; 151 xmlNodePtr tree, subtree; 152 153 doc = xmlNewDoc("1.0"); 154 doc->children = xmlNewDocNode(doc, NULL, "EXAMPLE", NULL); 155 xmlSetProp(doc->children, "prop1", "gnome is great"); 156 xmlSetProp(doc->children, "prop2", "& linux too"); 157 tree = xmlNewChild(doc->children, NULL, "head", NULL); 158 subtree = xmlNewChild(tree, NULL, "title", "Welcome to Gnome"); 159 tree = xmlNewChild(doc->children, NULL, "chapter", NULL); 160 subtree = xmlNewChild(tree, NULL, "title", "The Linux adventure"); 161 subtree = xmlNewChild(tree, NULL, "p", "bla bla bla ..."); 162 subtree = xmlNewChild(tree, NULL, "image", NULL); 163 xmlSetProp(subtree, "href", "linus.gif");</pre> 164<p>Not really rocket science ...</p> 165<h3><a name="Traversing">Traversing the tree</a></h3> 166<p>Basically by <a href="html/libxml-tree.html">including "tree.h"</a> your 167code has access to the internal structure of all the elements of the tree. 168The names should be somewhat simple like <strong>parent</strong>, 169<strong>children</strong>, <strong>next</strong>, <strong>prev</strong>, 170<strong>properties</strong>, etc... For example, still with the previous 171example:</p> 172<pre><code>doc->children->children->children</code></pre> 173<p>points to the title element,</p> 174<pre>doc->children->children->next->children->children</pre> 175<p>points to the text node containing the chapter title "The Linux 176adventure".</p> 177<p> 178<strong>NOTE</strong>: XML allows <em>PI</em>s and <em>comments</em> to be 179present before the document root, so <code>doc->children</code> may point 180to an element which is not the document Root Element; a function 181<code>xmlDocGetRootElement()</code> was added for this purpose.</p> 182<h3><a name="Modifying">Modifying the tree</a></h3> 183<p>Functions are provided for reading and writing the document content. Here 184is an excerpt from the <a href="html/libxml-tree.html">tree API</a>:</p> 185<dl> 186<dt><code>xmlAttrPtr xmlSetProp(xmlNodePtr node, const xmlChar *name, const 187 xmlChar *value);</code></dt> 188<dd><p>This sets (or changes) an attribute carried by an ELEMENT node. 189 The value can be NULL.</p></dd> 190</dl> 191<dl> 192<dt><code>const xmlChar *xmlGetProp(xmlNodePtr node, const xmlChar 193 *name);</code></dt> 194<dd><p>This function returns a pointer to new copy of the property 195 content. Note that the user must deallocate the result.</p></dd> 196</dl> 197<p>Two functions are provided for reading and writing the text associated 198with elements:</p> 199<dl> 200<dt><code>xmlNodePtr xmlStringGetNodeList(xmlDocPtr doc, const xmlChar 201 *value);</code></dt> 202<dd><p>This function takes an "external" string and converts it to one 203 text node or possibly to a list of entity and text nodes. All 204 non-predefined entity references like &Gnome; will be stored 205 internally as entity nodes, hence the result of the function may not be 206 a single node.</p></dd> 207</dl> 208<dl> 209<dt><code>xmlChar *xmlNodeListGetString(xmlDocPtr doc, xmlNodePtr list, int 210 inLine);</code></dt> 211<dd><p>This function is the inverse of 212 <code>xmlStringGetNodeList()</code>. It generates a new string 213 containing the content of the text and entity nodes. Note the extra 214 argument inLine. If this argument is set to 1, the function will expand 215 entity references. For example, instead of returning the &Gnome; 216 XML encoding in the string, it will substitute it with its value (say, 217 "GNU Network Object Model Environment").</p></dd> 218</dl> 219<h3><a name="Saving">Saving a tree</a></h3> 220<p>Basically 3 options are possible:</p> 221<dl> 222<dt><code>void xmlDocDumpMemory(xmlDocPtr cur, xmlChar**mem, int 223 *size);</code></dt> 224<dd><p>Returns a buffer into which the document has been saved.</p></dd> 225</dl> 226<dl> 227<dt><code>extern void xmlDocDump(FILE *f, xmlDocPtr doc);</code></dt> 228<dd><p>Dumps a document to an open file descriptor.</p></dd> 229</dl> 230<dl> 231<dt><code>int xmlSaveFile(const char *filename, xmlDocPtr cur);</code></dt> 232<dd><p>Saves the document to a file. In this case, the compression 233 interface is triggered if it has been turned on.</p></dd> 234</dl> 235<h3><a name="Compressio">Compression</a></h3> 236<p>The library transparently handles compression when doing file-based 237accesses. The level of compression on saves can be turned on either globally 238or individually for one file:</p> 239<dl> 240<dt><code>int xmlGetDocCompressMode (xmlDocPtr doc);</code></dt> 241<dd><p>Gets the document compression ratio (0-9).</p></dd> 242</dl> 243<dl> 244<dt><code>void xmlSetDocCompressMode (xmlDocPtr doc, int mode);</code></dt> 245<dd><p>Sets the document compression ratio.</p></dd> 246</dl> 247<dl> 248<dt><code>int xmlGetCompressMode(void);</code></dt> 249<dd><p>Gets the default compression ratio.</p></dd> 250</dl> 251<dl> 252<dt><code>void xmlSetCompressMode(int mode);</code></dt> 253<dd><p>Sets the default compression ratio.</p></dd> 254</dl> 255<p><a href="mailto:daniel@veillard.com">Daniel Veillard</a></p> 256</td></tr></table></td></tr></table></td></tr></table></td> 257</tr></table></td></tr></table> 258</body> 259</html> 260
