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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>
Daniel Veillard594cf0b2001-10-25 08:09:12 +0000[diff] [blame]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">
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 Veillard6dbcaf82002-02-20 14:37:47 +0000[diff] [blame]40<li><a href="python.html">Python and bindings</a></li>
Daniel Veillardb8cfbd12001-10-25 10:53:28 +0000[diff] [blame]41<li><a href="architecture.html">libxml architecture</a></li>
Daniel Veillardc9484202001-10-24 12:35:52 +0000[diff] [blame]42<li><a href="tree.html">The tree output</a></li>
43<li><a href="interface.html">The SAX interface</a></li>
Daniel Veillardb8cfbd12001-10-25 10:53:28 +0000[diff] [blame]44<li><a href="xmldtd.html">Validation &amp; DTDs</a></li>
45<li><a href="xmlmem.html">Memory Management</a></li>
46<li><a href="encoding.html">Encodings support</a></li>
47<li><a href="xmlio.html">I/O Interfaces</a></li>
48<li><a href="catalog.html">Catalog support</a></li>
49<li><a href="library.html">The parser interfaces</a></li>
Daniel Veillardc9484202001-10-24 12:35:52 +0000[diff] [blame]50<li><a href="entities.html">Entities or no entities</a></li>
51<li><a href="namespaces.html">Namespaces</a></li>
Daniel Veillardb8cfbd12001-10-25 10:53:28 +0000[diff] [blame]52<li><a href="upgrade.html">Upgrading 1.x code</a></li>
Daniel Veillard52dcab32001-10-30 12:51:17 +0000[diff] [blame]53<li><a href="threads.html">Thread safety</a></li>
Daniel Veillardc9484202001-10-24 12:35:52 +0000[diff] [blame]54<li><a href="DOM.html">DOM Principles</a></li>
55<li><a href="example.html">A real example</a></li>
56<li><a href="contribs.html">Contributions</a></li>
Daniel Veillard594cf0b2001-10-25 08:09:12 +0000[diff] [blame]57<li>
58<a href="xml.html">flat page</a>, <a href="site.xsl">stylesheet</a>
59</li>
Daniel Veillardc9484202001-10-24 12:35:52 +0000[diff] [blame]60</ul></td></tr>
Daniel Veillard594cf0b2001-10-25 08:09:12 +0000[diff] [blame]61</table>
62<table width="100%" border="0" cellspacing="1" cellpadding="3">
Daniel Veillard3bf65be2002-01-23 12:36:34 +0000[diff] [blame]63<tr><td colspan="1" bgcolor="#eecfa1" align="center"><center><b>API Indexes</b></center></td></tr>
64<tr><td bgcolor="#fffacd"><ul>
Daniel Veillardf8592562002-01-23 17:58:17 +0000[diff] [blame]65<li><a href="APIchunk0.html">Alphabetic</a></li>
Daniel Veillard3bf65be2002-01-23 12:36:34 +0000[diff] [blame]66<li><a href="APIconstructors.html">Constructors</a></li>
67<li><a href="APIfunctions.html">Functions/Types</a></li>
68<li><a href="APIfiles.html">Modules</a></li>
69<li><a href="APIsymbols.html">Symbols</a></li>
70</ul></td></tr>
71</table>
72<table width="100%" border="0" cellspacing="1" cellpadding="3">
Daniel Veillard594cf0b2001-10-25 08:09:12 +0000[diff] [blame]73<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]74<tr><td bgcolor="#fffacd"><ul>
Daniel Veillard594cf0b2001-10-25 08:09:12 +0000[diff] [blame]75<li><a href="http://mail.gnome.org/archives/xml/">Mail archive</a></li>
76<li><a href="http://xmlsoft.org/XSLT/">XSLT libxslt</a></li>
Daniel Veillard4a859202002-01-08 11:49:22 +0000[diff] [blame]77<li><a href="http://phd.cs.unibo.it/gdome2/">DOM gdome2</a></li>
Daniel Veillard594cf0b2001-10-25 08:09:12 +0000[diff] [blame]78<li><a href="ftp://xmlsoft.org/">FTP</a></li>
79<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]80<li><a href="http://garypennington.net/libxml2/">Solaris binaries</a></li>
Daniel Veillardc6271d22001-10-27 07:50:58 +0000[diff] [blame]81<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]82</ul></td></tr>
83</table>
84</td></tr></table></td>
Daniel Veillardc9484202001-10-24 12:35:52 +0000[diff] [blame]85<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">
86<p>This section is directly intended to help programmers getting bootstrapped
87using the XML library from the C language. It is not intended to be
88extensive. I hope the automatically generated documents will provide the
89completeness required, but as a separate set of documents. The interfaces of
90the XML library are by principle low level, there is nearly zero abstraction.
91Those interested in a higher level API should <a href="#DOM">look at
92DOM</a>.</p>
93<p>The <a href="html/libxml-parser.html">parser interfaces for XML</a> are
94separated from the <a href="html/libxml-htmlparser.html">HTML parser
95interfaces</a>. Let's have a look at how the XML parser can be called:</p>
96<h3><a name="Invoking">Invoking the parser : the pull method</a></h3>
97<p>Usually, the first thing to do is to read an XML input. The parser accepts
98documents either from in-memory strings or from files. The functions are
99defined in &quot;parser.h&quot;:</p>
100<dl>
101<dt><code>xmlDocPtr xmlParseMemory(char *buffer, int size);</code></dt>
102<dd><p>Parse a null-terminated string containing the document.</p></dd>
103</dl>
104<dl>
105<dt><code>xmlDocPtr xmlParseFile(const char *filename);</code></dt>
106<dd><p>Parse an XML document contained in a (possibly compressed)
107 file.</p></dd>
108</dl>
109<p>The parser returns a pointer to the document structure (or NULL in case of
110failure).</p>
111<h3 id="Invoking1">Invoking the parser: the push method</h3>
112<p>In order for the application to keep the control when the document is
113being fetched (which is common for GUI based programs) libxml provides a push
114interface, too, as of version 1.8.3. Here are the interface functions:</p>
115<pre>xmlParserCtxtPtr xmlCreatePushParserCtxt(xmlSAXHandlerPtr sax,
116 void *user_data,
117 const char *chunk,
118 int size,
119 const char *filename);
120int xmlParseChunk (xmlParserCtxtPtr ctxt,
121 const char *chunk,
122 int size,
123 int terminate);</pre>
124<p>and here is a simple example showing how to use the interface:</p>
125<pre> FILE *f;
126
127 f = fopen(filename, &quot;r&quot;);
128 if (f != NULL) {
129 int res, size = 1024;
130 char chars[1024];
131 xmlParserCtxtPtr ctxt;
132
133 res = fread(chars, 1, 4, f);
134 if (res &gt; 0) {
135 ctxt = xmlCreatePushParserCtxt(NULL, NULL,
136 chars, res, filename);
137 while ((res = fread(chars, 1, size, f)) &gt; 0) {
138 xmlParseChunk(ctxt, chars, res, 0);
139 }
140 xmlParseChunk(ctxt, chars, 0, 1);
141 doc = ctxt-&gt;myDoc;
142 xmlFreeParserCtxt(ctxt);
143 }
144 }</pre>
145<p>The HTML parser embedded into libxml also has a push interface; the
146functions are just prefixed by &quot;html&quot; rather than &quot;xml&quot;.</p>
147<h3 id="Invoking2">Invoking the parser: the SAX interface</h3>
148<p>The tree-building interface makes the parser memory-hungry, first loading
149the document in memory and then building the tree itself. Reading a document
150without building the tree is possible using the SAX interfaces (see SAX.h and
151<a href="http://www.daa.com.au/~james/gnome/xml-sax/xml-sax.html">James
152Henstridge's documentation</a>). Note also that the push interface can be
153limited to SAX: just use the two first arguments of
154<code>xmlCreatePushParserCtxt()</code>.</p>
155<h3><a name="Building">Building a tree from scratch</a></h3>
156<p>The other way to get an XML tree in memory is by building it. Basically
157there is a set of functions dedicated to building new elements. (These are
158also described in &lt;libxml/tree.h&gt;.) For example, here is a piece of
159code that produces the XML document used in the previous examples:</p>
160<pre> #include &lt;libxml/tree.h&gt;
161 xmlDocPtr doc;
162 xmlNodePtr tree, subtree;
163
164 doc = xmlNewDoc(&quot;1.0&quot;);
165 doc-&gt;children = xmlNewDocNode(doc, NULL, &quot;EXAMPLE&quot;, NULL);
166 xmlSetProp(doc-&gt;children, &quot;prop1&quot;, &quot;gnome is great&quot;);
167 xmlSetProp(doc-&gt;children, &quot;prop2&quot;, &quot;&amp; linux too&quot;);
168 tree = xmlNewChild(doc-&gt;children, NULL, &quot;head&quot;, NULL);
169 subtree = xmlNewChild(tree, NULL, &quot;title&quot;, &quot;Welcome to Gnome&quot;);
170 tree = xmlNewChild(doc-&gt;children, NULL, &quot;chapter&quot;, NULL);
171 subtree = xmlNewChild(tree, NULL, &quot;title&quot;, &quot;The Linux adventure&quot;);
172 subtree = xmlNewChild(tree, NULL, &quot;p&quot;, &quot;bla bla bla ...&quot;);
173 subtree = xmlNewChild(tree, NULL, &quot;image&quot;, NULL);
174 xmlSetProp(subtree, &quot;href&quot;, &quot;linus.gif&quot;);</pre>
175<p>Not really rocket science ...</p>
176<h3><a name="Traversing">Traversing the tree</a></h3>
177<p>Basically by <a href="html/libxml-tree.html">including &quot;tree.h&quot;</a> your
178code has access to the internal structure of all the elements of the tree.
179The names should be somewhat simple like <strong>parent</strong>,
180<strong>children</strong>, <strong>next</strong>, <strong>prev</strong>,
181<strong>properties</strong>, etc... For example, still with the previous
182example:</p>
183<pre><code>doc-&gt;children-&gt;children-&gt;children</code></pre>
184<p>points to the title element,</p>
185<pre>doc-&gt;children-&gt;children-&gt;next-&gt;children-&gt;children</pre>
186<p>points to the text node containing the chapter title &quot;The Linux
187adventure&quot;.</p>
188<p>
189<strong>NOTE</strong>: XML allows <em>PI</em>s and <em>comments</em> to be
190present before the document root, so <code>doc-&gt;children</code> may point
191to an element which is not the document Root Element; a function
192<code>xmlDocGetRootElement()</code> was added for this purpose.</p>
193<h3><a name="Modifying">Modifying the tree</a></h3>
194<p>Functions are provided for reading and writing the document content. Here
195is an excerpt from the <a href="html/libxml-tree.html">tree API</a>:</p>
196<dl>
197<dt><code>xmlAttrPtr xmlSetProp(xmlNodePtr node, const xmlChar *name, const
198 xmlChar *value);</code></dt>
199<dd><p>This sets (or changes) an attribute carried by an ELEMENT node.
200 The value can be NULL.</p></dd>
201</dl>
202<dl>
203<dt><code>const xmlChar *xmlGetProp(xmlNodePtr node, const xmlChar
204 *name);</code></dt>
205<dd><p>This function returns a pointer to new copy of the property
206 content. Note that the user must deallocate the result.</p></dd>
207</dl>
208<p>Two functions are provided for reading and writing the text associated
209with elements:</p>
210<dl>
211<dt><code>xmlNodePtr xmlStringGetNodeList(xmlDocPtr doc, const xmlChar
212 *value);</code></dt>
213<dd><p>This function takes an &quot;external&quot; string and converts it to one
214 text node or possibly to a list of entity and text nodes. All
215 non-predefined entity references like &amp;Gnome; will be stored
216 internally as entity nodes, hence the result of the function may not be
217 a single node.</p></dd>
218</dl>
219<dl>
220<dt><code>xmlChar *xmlNodeListGetString(xmlDocPtr doc, xmlNodePtr list, int
221 inLine);</code></dt>
222<dd><p>This function is the inverse of
223 <code>xmlStringGetNodeList()</code>. It generates a new string
224 containing the content of the text and entity nodes. Note the extra
225 argument inLine. If this argument is set to 1, the function will expand
226 entity references. For example, instead of returning the &amp;Gnome;
227 XML encoding in the string, it will substitute it with its value (say,
228 &quot;GNU Network Object Model Environment&quot;).</p></dd>
229</dl>
230<h3><a name="Saving">Saving a tree</a></h3>
231<p>Basically 3 options are possible:</p>
232<dl>
233<dt><code>void xmlDocDumpMemory(xmlDocPtr cur, xmlChar**mem, int
234 *size);</code></dt>
235<dd><p>Returns a buffer into which the document has been saved.</p></dd>
236</dl>
237<dl>
238<dt><code>extern void xmlDocDump(FILE *f, xmlDocPtr doc);</code></dt>
239<dd><p>Dumps a document to an open file descriptor.</p></dd>
240</dl>
241<dl>
242<dt><code>int xmlSaveFile(const char *filename, xmlDocPtr cur);</code></dt>
243<dd><p>Saves the document to a file. In this case, the compression
244 interface is triggered if it has been turned on.</p></dd>
245</dl>
246<h3><a name="Compressio">Compression</a></h3>
247<p>The library transparently handles compression when doing file-based
248accesses. The level of compression on saves can be turned on either globally
249or individually for one file:</p>
250<dl>
251<dt><code>int xmlGetDocCompressMode (xmlDocPtr doc);</code></dt>
252<dd><p>Gets the document compression ratio (0-9).</p></dd>
253</dl>
254<dl>
255<dt><code>void xmlSetDocCompressMode (xmlDocPtr doc, int mode);</code></dt>
256<dd><p>Sets the document compression ratio.</p></dd>
257</dl>
258<dl>
259<dt><code>int xmlGetCompressMode(void);</code></dt>
260<dd><p>Gets the default compression ratio.</p></dd>
261</dl>
262<dl>
263<dt><code>void xmlSetCompressMode(int mode);</code></dt>
264<dd><p>Sets the default compression ratio.</p></dd>
265</dl>
Daniel Veillard3f4c40f2002-02-13 09:19:28 +0000[diff] [blame]266<p><a href="bugs.html">Daniel Veillard</a></p>
Daniel Veillardc9484202001-10-24 12:35:52 +0000[diff] [blame]267</td></tr></table></td></tr></table></td></tr></table></td>
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