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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>
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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>
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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>
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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>
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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>
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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>
Daniel Veillardc6271d22001-10-27 07:50:58 +0000[diff] [blame]70<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]71</ul></td></tr>
72</table>
73</td></tr></table></td>
Daniel Veillardc9484202001-10-24 12:35:52 +0000[diff] [blame]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 &quot;parser.h&quot;:</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, &quot;r&quot;);
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 &gt; 0) {
124 ctxt = xmlCreatePushParserCtxt(NULL, NULL,
125 chars, res, filename);
126 while ((res = fread(chars, 1, size, f)) &gt; 0) {
127 xmlParseChunk(ctxt, chars, res, 0);
128 }
129 xmlParseChunk(ctxt, chars, 0, 1);
130 doc = ctxt-&gt;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 &quot;html&quot; rather than &quot;xml&quot;.</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 &lt;libxml/tree.h&gt;.) For example, here is a piece of
148code that produces the XML document used in the previous examples:</p>
149<pre> #include &lt;libxml/tree.h&gt;
150 xmlDocPtr doc;
151 xmlNodePtr tree, subtree;
152
153 doc = xmlNewDoc(&quot;1.0&quot;);
154 doc-&gt;children = xmlNewDocNode(doc, NULL, &quot;EXAMPLE&quot;, NULL);
155 xmlSetProp(doc-&gt;children, &quot;prop1&quot;, &quot;gnome is great&quot;);
156 xmlSetProp(doc-&gt;children, &quot;prop2&quot;, &quot;&amp; linux too&quot;);
157 tree = xmlNewChild(doc-&gt;children, NULL, &quot;head&quot;, NULL);
158 subtree = xmlNewChild(tree, NULL, &quot;title&quot;, &quot;Welcome to Gnome&quot;);
159 tree = xmlNewChild(doc-&gt;children, NULL, &quot;chapter&quot;, NULL);
160 subtree = xmlNewChild(tree, NULL, &quot;title&quot;, &quot;The Linux adventure&quot;);
161 subtree = xmlNewChild(tree, NULL, &quot;p&quot;, &quot;bla bla bla ...&quot;);
162 subtree = xmlNewChild(tree, NULL, &quot;image&quot;, NULL);
163 xmlSetProp(subtree, &quot;href&quot;, &quot;linus.gif&quot;);</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 &quot;tree.h&quot;</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-&gt;children-&gt;children-&gt;children</code></pre>
173<p>points to the title element,</p>
174<pre>doc-&gt;children-&gt;children-&gt;next-&gt;children-&gt;children</pre>
175<p>points to the text node containing the chapter title &quot;The Linux
176adventure&quot;.</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-&gt;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 &quot;external&quot; 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 &amp;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 &amp;Gnome;
216 XML encoding in the string, it will substitute it with its value (say,
217 &quot;GNU Network Object Model Environment&quot;).</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>
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