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Daniel Veillardb8cfbd12001-10-25 10:53:28 +0000[diff] [blame^]13<title>The parser interfaces</title>
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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>
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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>
29<tr><td bgcolor="#fffacd"><ul style="margin-left: -2pt">
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>
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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 Veillardc9484202001-10-24 12:35:52 +0000[diff] [blame]52<li><a href="DOM.html">DOM Principles</a></li>
53<li><a href="example.html">A real example</a></li>
54<li><a href="contribs.html">Contributions</a></li>
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Daniel Veillardc9484202001-10-24 12:35:52 +0000[diff] [blame]58</ul></td></tr>
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60<table width="100%" border="0" cellspacing="1" cellpadding="3">
61<tr><td colspan="1" bgcolor="#eecfa1" align="center"><center><b>Related links</b></center></td></tr>
62<tr><td bgcolor="#fffacd"><ul style="margin-left: -2pt">
63<li><a href="http://mail.gnome.org/archives/xml/">Mail archive</a></li>
64<li><a href="http://xmlsoft.org/XSLT/">XSLT libxslt</a></li>
65<li><a href="http://www.cs.unibo.it/~casarini/gdome2/">DOM gdome2</a></li>
66<li><a href="ftp://xmlsoft.org/">FTP</a></li>
67<li><a href="http://www.fh-frankfurt.de/~igor/projects/libxml/">Windows binaries</a></li>
68<li><a href="http://pages.eidosnet.co.uk/~garypen/libxml/">Solaris binaries</a></li>
69</ul></td></tr>
70</table>
71</td></tr></table></td>
Daniel Veillardc9484202001-10-24 12:35:52 +0000[diff] [blame]72<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">
73<p>This section is directly intended to help programmers getting bootstrapped
74using the XML library from the C language. It is not intended to be
75extensive. I hope the automatically generated documents will provide the
76completeness required, but as a separate set of documents. The interfaces of
77the XML library are by principle low level, there is nearly zero abstraction.
78Those interested in a higher level API should <a href="#DOM">look at
79DOM</a>.</p>
80<p>The <a href="html/libxml-parser.html">parser interfaces for XML</a> are
81separated from the <a href="html/libxml-htmlparser.html">HTML parser
82interfaces</a>. Let's have a look at how the XML parser can be called:</p>
83<h3><a name="Invoking">Invoking the parser : the pull method</a></h3>
84<p>Usually, the first thing to do is to read an XML input. The parser accepts
85documents either from in-memory strings or from files. The functions are
86defined in &quot;parser.h&quot;:</p>
87<dl>
88<dt><code>xmlDocPtr xmlParseMemory(char *buffer, int size);</code></dt>
89<dd><p>Parse a null-terminated string containing the document.</p></dd>
90</dl>
91<dl>
92<dt><code>xmlDocPtr xmlParseFile(const char *filename);</code></dt>
93<dd><p>Parse an XML document contained in a (possibly compressed)
94 file.</p></dd>
95</dl>
96<p>The parser returns a pointer to the document structure (or NULL in case of
97failure).</p>
98<h3 id="Invoking1">Invoking the parser: the push method</h3>
99<p>In order for the application to keep the control when the document is
100being fetched (which is common for GUI based programs) libxml provides a push
101interface, too, as of version 1.8.3. Here are the interface functions:</p>
102<pre>xmlParserCtxtPtr xmlCreatePushParserCtxt(xmlSAXHandlerPtr sax,
103 void *user_data,
104 const char *chunk,
105 int size,
106 const char *filename);
107int xmlParseChunk (xmlParserCtxtPtr ctxt,
108 const char *chunk,
109 int size,
110 int terminate);</pre>
111<p>and here is a simple example showing how to use the interface:</p>
112<pre> FILE *f;
113
114 f = fopen(filename, &quot;r&quot;);
115 if (f != NULL) {
116 int res, size = 1024;
117 char chars[1024];
118 xmlParserCtxtPtr ctxt;
119
120 res = fread(chars, 1, 4, f);
121 if (res &gt; 0) {
122 ctxt = xmlCreatePushParserCtxt(NULL, NULL,
123 chars, res, filename);
124 while ((res = fread(chars, 1, size, f)) &gt; 0) {
125 xmlParseChunk(ctxt, chars, res, 0);
126 }
127 xmlParseChunk(ctxt, chars, 0, 1);
128 doc = ctxt-&gt;myDoc;
129 xmlFreeParserCtxt(ctxt);
130 }
131 }</pre>
132<p>The HTML parser embedded into libxml also has a push interface; the
133functions are just prefixed by &quot;html&quot; rather than &quot;xml&quot;.</p>
134<h3 id="Invoking2">Invoking the parser: the SAX interface</h3>
135<p>The tree-building interface makes the parser memory-hungry, first loading
136the document in memory and then building the tree itself. Reading a document
137without building the tree is possible using the SAX interfaces (see SAX.h and
138<a href="http://www.daa.com.au/~james/gnome/xml-sax/xml-sax.html">James
139Henstridge's documentation</a>). Note also that the push interface can be
140limited to SAX: just use the two first arguments of
141<code>xmlCreatePushParserCtxt()</code>.</p>
142<h3><a name="Building">Building a tree from scratch</a></h3>
143<p>The other way to get an XML tree in memory is by building it. Basically
144there is a set of functions dedicated to building new elements. (These are
145also described in &lt;libxml/tree.h&gt;.) For example, here is a piece of
146code that produces the XML document used in the previous examples:</p>
147<pre> #include &lt;libxml/tree.h&gt;
148 xmlDocPtr doc;
149 xmlNodePtr tree, subtree;
150
151 doc = xmlNewDoc(&quot;1.0&quot;);
152 doc-&gt;children = xmlNewDocNode(doc, NULL, &quot;EXAMPLE&quot;, NULL);
153 xmlSetProp(doc-&gt;children, &quot;prop1&quot;, &quot;gnome is great&quot;);
154 xmlSetProp(doc-&gt;children, &quot;prop2&quot;, &quot;&amp; linux too&quot;);
155 tree = xmlNewChild(doc-&gt;children, NULL, &quot;head&quot;, NULL);
156 subtree = xmlNewChild(tree, NULL, &quot;title&quot;, &quot;Welcome to Gnome&quot;);
157 tree = xmlNewChild(doc-&gt;children, NULL, &quot;chapter&quot;, NULL);
158 subtree = xmlNewChild(tree, NULL, &quot;title&quot;, &quot;The Linux adventure&quot;);
159 subtree = xmlNewChild(tree, NULL, &quot;p&quot;, &quot;bla bla bla ...&quot;);
160 subtree = xmlNewChild(tree, NULL, &quot;image&quot;, NULL);
161 xmlSetProp(subtree, &quot;href&quot;, &quot;linus.gif&quot;);</pre>
162<p>Not really rocket science ...</p>
163<h3><a name="Traversing">Traversing the tree</a></h3>
164<p>Basically by <a href="html/libxml-tree.html">including &quot;tree.h&quot;</a> your
165code has access to the internal structure of all the elements of the tree.
166The names should be somewhat simple like <strong>parent</strong>,
167<strong>children</strong>, <strong>next</strong>, <strong>prev</strong>,
168<strong>properties</strong>, etc... For example, still with the previous
169example:</p>
170<pre><code>doc-&gt;children-&gt;children-&gt;children</code></pre>
171<p>points to the title element,</p>
172<pre>doc-&gt;children-&gt;children-&gt;next-&gt;children-&gt;children</pre>
173<p>points to the text node containing the chapter title &quot;The Linux
174adventure&quot;.</p>
175<p>
176<strong>NOTE</strong>: XML allows <em>PI</em>s and <em>comments</em> to be
177present before the document root, so <code>doc-&gt;children</code> may point
178to an element which is not the document Root Element; a function
179<code>xmlDocGetRootElement()</code> was added for this purpose.</p>
180<h3><a name="Modifying">Modifying the tree</a></h3>
181<p>Functions are provided for reading and writing the document content. Here
182is an excerpt from the <a href="html/libxml-tree.html">tree API</a>:</p>
183<dl>
184<dt><code>xmlAttrPtr xmlSetProp(xmlNodePtr node, const xmlChar *name, const
185 xmlChar *value);</code></dt>
186<dd><p>This sets (or changes) an attribute carried by an ELEMENT node.
187 The value can be NULL.</p></dd>
188</dl>
189<dl>
190<dt><code>const xmlChar *xmlGetProp(xmlNodePtr node, const xmlChar
191 *name);</code></dt>
192<dd><p>This function returns a pointer to new copy of the property
193 content. Note that the user must deallocate the result.</p></dd>
194</dl>
195<p>Two functions are provided for reading and writing the text associated
196with elements:</p>
197<dl>
198<dt><code>xmlNodePtr xmlStringGetNodeList(xmlDocPtr doc, const xmlChar
199 *value);</code></dt>
200<dd><p>This function takes an &quot;external&quot; string and converts it to one
201 text node or possibly to a list of entity and text nodes. All
202 non-predefined entity references like &amp;Gnome; will be stored
203 internally as entity nodes, hence the result of the function may not be
204 a single node.</p></dd>
205</dl>
206<dl>
207<dt><code>xmlChar *xmlNodeListGetString(xmlDocPtr doc, xmlNodePtr list, int
208 inLine);</code></dt>
209<dd><p>This function is the inverse of
210 <code>xmlStringGetNodeList()</code>. It generates a new string
211 containing the content of the text and entity nodes. Note the extra
212 argument inLine. If this argument is set to 1, the function will expand
213 entity references. For example, instead of returning the &amp;Gnome;
214 XML encoding in the string, it will substitute it with its value (say,
215 &quot;GNU Network Object Model Environment&quot;).</p></dd>
216</dl>
217<h3><a name="Saving">Saving a tree</a></h3>
218<p>Basically 3 options are possible:</p>
219<dl>
220<dt><code>void xmlDocDumpMemory(xmlDocPtr cur, xmlChar**mem, int
221 *size);</code></dt>
222<dd><p>Returns a buffer into which the document has been saved.</p></dd>
223</dl>
224<dl>
225<dt><code>extern void xmlDocDump(FILE *f, xmlDocPtr doc);</code></dt>
226<dd><p>Dumps a document to an open file descriptor.</p></dd>
227</dl>
228<dl>
229<dt><code>int xmlSaveFile(const char *filename, xmlDocPtr cur);</code></dt>
230<dd><p>Saves the document to a file. In this case, the compression
231 interface is triggered if it has been turned on.</p></dd>
232</dl>
233<h3><a name="Compressio">Compression</a></h3>
234<p>The library transparently handles compression when doing file-based
235accesses. The level of compression on saves can be turned on either globally
236or individually for one file:</p>
237<dl>
238<dt><code>int xmlGetDocCompressMode (xmlDocPtr doc);</code></dt>
239<dd><p>Gets the document compression ratio (0-9).</p></dd>
240</dl>
241<dl>
242<dt><code>void xmlSetDocCompressMode (xmlDocPtr doc, int mode);</code></dt>
243<dd><p>Sets the document compression ratio.</p></dd>
244</dl>
245<dl>
246<dt><code>int xmlGetCompressMode(void);</code></dt>
247<dd><p>Gets the default compression ratio.</p></dd>
248</dl>
249<dl>
250<dt><code>void xmlSetCompressMode(int mode);</code></dt>
251<dd><p>Sets the default compression ratio.</p></dd>
252</dl>
253<p><a href="mailto:daniel@veillard.com">Daniel Veillard</a></p>
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