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Daniel Veillardb8cfbd12001-10-25 10:53:28 +0000[diff] [blame]13<title>The parser interfaces</title>
Daniel Veillardc9484202001-10-24 12:35:52 +0000[diff] [blame]14</head>
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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>
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21<h1>The XML C library for Gnome</h1>
Daniel Veillardb8cfbd12001-10-25 10:53:28 +0000[diff] [blame]22<h2>The parser interfaces</h2>
Daniel Veillardc9484202001-10-24 12:35:52 +0000[diff] [blame]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>
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27<table width="100%" border="0" cellspacing="1" cellpadding="3">
Daniel Veillardc9484202001-10-24 12:35:52 +0000[diff] [blame]28<tr><td colspan="1" bgcolor="#eecfa1" align="center"><center><b>Main Menu</b></center></td></tr>
Daniel Veillard8acca112002-01-21 09:52:27 +0000[diff] [blame]29<tr><td bgcolor="#fffacd"><ul>
Daniel Veillardc9484202001-10-24 12:35:52 +0000[diff] [blame]30<li><a href="index.html">Home</a></li>
Daniel Veillardc9484202001-10-24 12:35:52 +0000[diff] [blame]31<li><a href="intro.html">Introduction</a></li>
Daniel Veillardb8cfbd12001-10-25 10:53:28 +0000[diff] [blame]32<li><a href="FAQ.html">FAQ</a></li>
Daniel Veillardc9484202001-10-24 12:35:52 +0000[diff] [blame]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>
Daniel Veillard7b602b42002-01-08 13:26:00 +0000[diff] [blame]38<li><a href="XMLinfo.html">XML</a></li>
Daniel Veillardc9484202001-10-24 12:35:52 +0000[diff] [blame]39<li><a href="XSLT.html">XSLT</a></li>
Daniel Veillardb8cfbd12001-10-25 10:53:28 +0000[diff] [blame]40<li><a href="architecture.html">libxml architecture</a></li>
Daniel Veillardc9484202001-10-24 12:35:52 +0000[diff] [blame]41<li><a href="tree.html">The tree output</a></li>
42<li><a href="interface.html">The SAX interface</a></li>
Daniel Veillardb8cfbd12001-10-25 10:53:28 +0000[diff] [blame]43<li><a href="xmldtd.html">Validation &amp; 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>
Daniel Veillardc9484202001-10-24 12:35:52 +0000[diff] [blame]49<li><a href="entities.html">Entities or no entities</a></li>
50<li><a href="namespaces.html">Namespaces</a></li>
Daniel Veillardb8cfbd12001-10-25 10:53:28 +0000[diff] [blame]51<li><a href="upgrade.html">Upgrading 1.x code</a></li>
Daniel Veillard52dcab32001-10-30 12:51:17 +0000[diff] [blame]52<li><a href="threads.html">Thread safety</a></li>
Daniel Veillardc9484202001-10-24 12:35:52 +0000[diff] [blame]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>
Daniel Veillard594cf0b2001-10-25 08:09:12 +0000[diff] [blame]56<li>
57<a href="xml.html">flat page</a>, <a href="site.xsl">stylesheet</a>
58</li>
Daniel Veillardc9484202001-10-24 12:35:52 +0000[diff] [blame]59</ul></td></tr>
Daniel Veillard594cf0b2001-10-25 08:09:12 +0000[diff] [blame]60</table>
61<table width="100%" border="0" cellspacing="1" cellpadding="3">
Daniel Veillard3bf65be2002-01-23 12:36:34 +0000[diff] [blame^]62<tr><td colspan="1" bgcolor="#eecfa1" align="center"><center><b>API Indexes</b></center></td></tr>
63<tr><td bgcolor="#fffacd"><ul>
64<li><a href="APIconstructors.html">Constructors</a></li>
65<li><a href="APIfunctions.html">Functions/Types</a></li>
66<li><a href="APIfiles.html">Modules</a></li>
67<li><a href="APIsymbols.html">Symbols</a></li>
68</ul></td></tr>
69</table>
70<table width="100%" border="0" cellspacing="1" cellpadding="3">
Daniel Veillard594cf0b2001-10-25 08:09:12 +0000[diff] [blame]71<tr><td colspan="1" bgcolor="#eecfa1" align="center"><center><b>Related links</b></center></td></tr>
Daniel Veillard8acca112002-01-21 09:52:27 +0000[diff] [blame]72<tr><td bgcolor="#fffacd"><ul>
Daniel Veillard594cf0b2001-10-25 08:09:12 +0000[diff] [blame]73<li><a href="http://mail.gnome.org/archives/xml/">Mail archive</a></li>
74<li><a href="http://xmlsoft.org/XSLT/">XSLT libxslt</a></li>
Daniel Veillard4a859202002-01-08 11:49:22 +0000[diff] [blame]75<li><a href="http://phd.cs.unibo.it/gdome2/">DOM gdome2</a></li>
Daniel Veillard594cf0b2001-10-25 08:09:12 +0000[diff] [blame]76<li><a href="ftp://xmlsoft.org/">FTP</a></li>
77<li><a href="http://www.fh-frankfurt.de/~igor/projects/libxml/">Windows binaries</a></li>
Daniel Veillarddb9dfd92001-11-26 17:25:02 +0000[diff] [blame]78<li><a href="http://garypennington.net/libxml2/">Solaris binaries</a></li>
Daniel Veillardc6271d22001-10-27 07:50:58 +0000[diff] [blame]79<li><a href="http://bugzilla.gnome.org/buglist.cgi?product=libxml">Bug Tracker</a></li>
Daniel Veillard594cf0b2001-10-25 08:09:12 +0000[diff] [blame]80</ul></td></tr>
81</table>
82</td></tr></table></td>
Daniel Veillardc9484202001-10-24 12:35:52 +0000[diff] [blame]83<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">
84<p>This section is directly intended to help programmers getting bootstrapped
85using the XML library from the C language. It is not intended to be
86extensive. I hope the automatically generated documents will provide the
87completeness required, but as a separate set of documents. The interfaces of
88the XML library are by principle low level, there is nearly zero abstraction.
89Those interested in a higher level API should <a href="#DOM">look at
90DOM</a>.</p>
91<p>The <a href="html/libxml-parser.html">parser interfaces for XML</a> are
92separated from the <a href="html/libxml-htmlparser.html">HTML parser
93interfaces</a>. Let's have a look at how the XML parser can be called:</p>
94<h3><a name="Invoking">Invoking the parser : the pull method</a></h3>
95<p>Usually, the first thing to do is to read an XML input. The parser accepts
96documents either from in-memory strings or from files. The functions are
97defined in &quot;parser.h&quot;:</p>
98<dl>
99<dt><code>xmlDocPtr xmlParseMemory(char *buffer, int size);</code></dt>
100<dd><p>Parse a null-terminated string containing the document.</p></dd>
101</dl>
102<dl>
103<dt><code>xmlDocPtr xmlParseFile(const char *filename);</code></dt>
104<dd><p>Parse an XML document contained in a (possibly compressed)
105 file.</p></dd>
106</dl>
107<p>The parser returns a pointer to the document structure (or NULL in case of
108failure).</p>
109<h3 id="Invoking1">Invoking the parser: the push method</h3>
110<p>In order for the application to keep the control when the document is
111being fetched (which is common for GUI based programs) libxml provides a push
112interface, too, as of version 1.8.3. Here are the interface functions:</p>
113<pre>xmlParserCtxtPtr xmlCreatePushParserCtxt(xmlSAXHandlerPtr sax,
114 void *user_data,
115 const char *chunk,
116 int size,
117 const char *filename);
118int xmlParseChunk (xmlParserCtxtPtr ctxt,
119 const char *chunk,
120 int size,
121 int terminate);</pre>
122<p>and here is a simple example showing how to use the interface:</p>
123<pre> FILE *f;
124
125 f = fopen(filename, &quot;r&quot;);
126 if (f != NULL) {
127 int res, size = 1024;
128 char chars[1024];
129 xmlParserCtxtPtr ctxt;
130
131 res = fread(chars, 1, 4, f);
132 if (res &gt; 0) {
133 ctxt = xmlCreatePushParserCtxt(NULL, NULL,
134 chars, res, filename);
135 while ((res = fread(chars, 1, size, f)) &gt; 0) {
136 xmlParseChunk(ctxt, chars, res, 0);
137 }
138 xmlParseChunk(ctxt, chars, 0, 1);
139 doc = ctxt-&gt;myDoc;
140 xmlFreeParserCtxt(ctxt);
141 }
142 }</pre>
143<p>The HTML parser embedded into libxml also has a push interface; the
144functions are just prefixed by &quot;html&quot; rather than &quot;xml&quot;.</p>
145<h3 id="Invoking2">Invoking the parser: the SAX interface</h3>
146<p>The tree-building interface makes the parser memory-hungry, first loading
147the document in memory and then building the tree itself. Reading a document
148without building the tree is possible using the SAX interfaces (see SAX.h and
149<a href="http://www.daa.com.au/~james/gnome/xml-sax/xml-sax.html">James
150Henstridge's documentation</a>). Note also that the push interface can be
151limited to SAX: just use the two first arguments of
152<code>xmlCreatePushParserCtxt()</code>.</p>
153<h3><a name="Building">Building a tree from scratch</a></h3>
154<p>The other way to get an XML tree in memory is by building it. Basically
155there is a set of functions dedicated to building new elements. (These are
156also described in &lt;libxml/tree.h&gt;.) For example, here is a piece of
157code that produces the XML document used in the previous examples:</p>
158<pre> #include &lt;libxml/tree.h&gt;
159 xmlDocPtr doc;
160 xmlNodePtr tree, subtree;
161
162 doc = xmlNewDoc(&quot;1.0&quot;);
163 doc-&gt;children = xmlNewDocNode(doc, NULL, &quot;EXAMPLE&quot;, NULL);
164 xmlSetProp(doc-&gt;children, &quot;prop1&quot;, &quot;gnome is great&quot;);
165 xmlSetProp(doc-&gt;children, &quot;prop2&quot;, &quot;&amp; linux too&quot;);
166 tree = xmlNewChild(doc-&gt;children, NULL, &quot;head&quot;, NULL);
167 subtree = xmlNewChild(tree, NULL, &quot;title&quot;, &quot;Welcome to Gnome&quot;);
168 tree = xmlNewChild(doc-&gt;children, NULL, &quot;chapter&quot;, NULL);
169 subtree = xmlNewChild(tree, NULL, &quot;title&quot;, &quot;The Linux adventure&quot;);
170 subtree = xmlNewChild(tree, NULL, &quot;p&quot;, &quot;bla bla bla ...&quot;);
171 subtree = xmlNewChild(tree, NULL, &quot;image&quot;, NULL);
172 xmlSetProp(subtree, &quot;href&quot;, &quot;linus.gif&quot;);</pre>
173<p>Not really rocket science ...</p>
174<h3><a name="Traversing">Traversing the tree</a></h3>
175<p>Basically by <a href="html/libxml-tree.html">including &quot;tree.h&quot;</a> your
176code has access to the internal structure of all the elements of the tree.
177The names should be somewhat simple like <strong>parent</strong>,
178<strong>children</strong>, <strong>next</strong>, <strong>prev</strong>,
179<strong>properties</strong>, etc... For example, still with the previous
180example:</p>
181<pre><code>doc-&gt;children-&gt;children-&gt;children</code></pre>
182<p>points to the title element,</p>
183<pre>doc-&gt;children-&gt;children-&gt;next-&gt;children-&gt;children</pre>
184<p>points to the text node containing the chapter title &quot;The Linux
185adventure&quot;.</p>
186<p>
187<strong>NOTE</strong>: XML allows <em>PI</em>s and <em>comments</em> to be
188present before the document root, so <code>doc-&gt;children</code> may point
189to an element which is not the document Root Element; a function
190<code>xmlDocGetRootElement()</code> was added for this purpose.</p>
191<h3><a name="Modifying">Modifying the tree</a></h3>
192<p>Functions are provided for reading and writing the document content. Here
193is an excerpt from the <a href="html/libxml-tree.html">tree API</a>:</p>
194<dl>
195<dt><code>xmlAttrPtr xmlSetProp(xmlNodePtr node, const xmlChar *name, const
196 xmlChar *value);</code></dt>
197<dd><p>This sets (or changes) an attribute carried by an ELEMENT node.
198 The value can be NULL.</p></dd>
199</dl>
200<dl>
201<dt><code>const xmlChar *xmlGetProp(xmlNodePtr node, const xmlChar
202 *name);</code></dt>
203<dd><p>This function returns a pointer to new copy of the property
204 content. Note that the user must deallocate the result.</p></dd>
205</dl>
206<p>Two functions are provided for reading and writing the text associated
207with elements:</p>
208<dl>
209<dt><code>xmlNodePtr xmlStringGetNodeList(xmlDocPtr doc, const xmlChar
210 *value);</code></dt>
211<dd><p>This function takes an &quot;external&quot; string and converts it to one
212 text node or possibly to a list of entity and text nodes. All
213 non-predefined entity references like &amp;Gnome; will be stored
214 internally as entity nodes, hence the result of the function may not be
215 a single node.</p></dd>
216</dl>
217<dl>
218<dt><code>xmlChar *xmlNodeListGetString(xmlDocPtr doc, xmlNodePtr list, int
219 inLine);</code></dt>
220<dd><p>This function is the inverse of
221 <code>xmlStringGetNodeList()</code>. It generates a new string
222 containing the content of the text and entity nodes. Note the extra
223 argument inLine. If this argument is set to 1, the function will expand
224 entity references. For example, instead of returning the &amp;Gnome;
225 XML encoding in the string, it will substitute it with its value (say,
226 &quot;GNU Network Object Model Environment&quot;).</p></dd>
227</dl>
228<h3><a name="Saving">Saving a tree</a></h3>
229<p>Basically 3 options are possible:</p>
230<dl>
231<dt><code>void xmlDocDumpMemory(xmlDocPtr cur, xmlChar**mem, int
232 *size);</code></dt>
233<dd><p>Returns a buffer into which the document has been saved.</p></dd>
234</dl>
235<dl>
236<dt><code>extern void xmlDocDump(FILE *f, xmlDocPtr doc);</code></dt>
237<dd><p>Dumps a document to an open file descriptor.</p></dd>
238</dl>
239<dl>
240<dt><code>int xmlSaveFile(const char *filename, xmlDocPtr cur);</code></dt>
241<dd><p>Saves the document to a file. In this case, the compression
242 interface is triggered if it has been turned on.</p></dd>
243</dl>
244<h3><a name="Compressio">Compression</a></h3>
245<p>The library transparently handles compression when doing file-based
246accesses. The level of compression on saves can be turned on either globally
247or individually for one file:</p>
248<dl>
249<dt><code>int xmlGetDocCompressMode (xmlDocPtr doc);</code></dt>
250<dd><p>Gets the document compression ratio (0-9).</p></dd>
251</dl>
252<dl>
253<dt><code>void xmlSetDocCompressMode (xmlDocPtr doc, int mode);</code></dt>
254<dd><p>Sets the document compression ratio.</p></dd>
255</dl>
256<dl>
257<dt><code>int xmlGetCompressMode(void);</code></dt>
258<dd><p>Gets the default compression ratio.</p></dd>
259</dl>
260<dl>
261<dt><code>void xmlSetCompressMode(int mode);</code></dt>
262<dd><p>Sets the default compression ratio.</p></dd>
263</dl>
264<p><a href="mailto:daniel@veillard.com">Daniel Veillard</a></p>
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