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| </style><title>The parser interfaces</title></head><body bgcolor="#8b7765" text="#000000" link="#a06060" vlink="#000000"><table border="0" width="100%" cellpadding="5" cellspacing="0" align="center"><tr><td width="120"><a href="http://swpat.ffii.org/"><img src="epatents.png" alt="Action against software patents" /></a></td><td width="180"><a href="http://www.gnome.org/"><img src="gnome2.png" alt="Gnome2 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><div align="left"><a href="http://xmlsoft.org/"><img src="Libxml2-Logo-180x168.gif" alt="Made with Libxml2 Logo" /></a></div></td><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"><h1>The XML C parser and toolkit of Gnome</h1><h2>The parser interfaces</h2></td></tr></table></td></tr></table></td></tr></table><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><td valign="top" width="200" bgcolor="#8b7765"><table border="0" cellspacing="0" cellpadding="1" width="100%" bgcolor="#000000"><tr><td><table width="100%" border="0" cellspacing="1" cellpadding="3"><tr><td colspan="1" bgcolor="#eecfa1" align="center"><center><b>Developer Menu</b></center></td></tr><tr><td bgcolor="#fffacd"><form action="search.php" enctype="application/x-www-form-urlencoded" method="get"><input name="query" type="text" size="20" value="" /><input name="submit" type="submit" value="Search ..." /></form><ul><li><a href="index.html" style="font-weight:bold">Main Menu</a></li><li><a href="html/index.html" style="font-weight:bold">Reference Manual</a></li><li><a href="examples/index.html" style="font-weight:bold">Code 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bgcolor="#000000"><tr><td><table border="0" cellpadding="3" cellspacing="1" width="100%"><tr><td bgcolor="#fffacd"><p>This section is directly intended to help programmers getting |
| bootstrappedusing the XML tollkit from the C language. It is not intended to |
| beextensive. I hope the automatically generated documents will provide |
| thecompleteness required, but as a separate set of documents. The interfaces |
| ofthe XML parser are by principle low level, Those interested in a higher |
| levelAPI should <a href="#DOM">look at DOM</a>.</p><p>The <a href="html/libxml-parser.html">parser interfaces for |
| XML</a>areseparated from the <a href="html/libxml-htmlparser.html">HTML |
| parserinterfaces</a>. Let's have a look at how the XML parser can be |
| called:</p><h3><a name="Invoking" id="Invoking">Invoking the parser : the pull method</a></h3><p>Usually, the first thing to do is to read an XML input. The parser |
| acceptsdocuments either from in-memory strings or from files. The functions |
| aredefined in "parser.h":</p><dl><dt><code>xmlDocPtr xmlParseMemory(char *buffer, int size);</code></dt> |
| <dd><p>Parse a null-terminated string containing the document.</p> |
| </dd> |
| </dl><dl><dt><code>xmlDocPtr xmlParseFile(const char *filename);</code></dt> |
| <dd><p>Parse an XML document contained in a (possibly compressed)file.</p> |
| </dd> |
| </dl><p>The parser returns a pointer to the document structure (or NULL in case |
| offailure).</p><h3 id="Invoking1">Invoking the parser: the push method</h3><p>In order for the application to keep the control when the document isbeing |
| fetched (which is common for GUI based programs) libxml2 provides apush |
| interface, too, as of version 1.8.3. Here are the interfacefunctions:</p><pre>xmlParserCtxtPtr xmlCreatePushParserCtxt(xmlSAXHandlerPtr sax, |
| void *user_data, |
| const char *chunk, |
| int size, |
| const char *filename); |
| int xmlParseChunk (xmlParserCtxtPtr ctxt, |
| const char *chunk, |
| int size, |
| int terminate);</pre><p>and here is a simple example showing how to use the interface:</p><pre> FILE *f; |
| |
| f = fopen(filename, "r"); |
| if (f != NULL) { |
| int res, size = 1024; |
| char chars[1024]; |
| xmlParserCtxtPtr ctxt; |
| |
| res = fread(chars, 1, 4, f); |
| if (res > 0) { |
| ctxt = xmlCreatePushParserCtxt(NULL, NULL, |
| chars, res, filename); |
| while ((res = fread(chars, 1, size, f)) > 0) { |
| xmlParseChunk(ctxt, chars, res, 0); |
| } |
| xmlParseChunk(ctxt, chars, 0, 1); |
| doc = ctxt->myDoc; |
| xmlFreeParserCtxt(ctxt); |
| } |
| }</pre><p>The HTML parser embedded into libxml2 also has a push interface; |
| thefunctions are just prefixed by "html" rather than "xml".</p><h3 id="Invoking2">Invoking the parser: the SAX interface</h3><p>The tree-building interface makes the parser memory-hungry, first |
| loadingthe document in memory and then building the tree itself. Reading a |
| documentwithout building the tree is possible using the SAX interfaces (see |
| SAX.h and<a href="http://www.daa.com.au/~james/gnome/xml-sax/xml-sax.html">JamesHenstridge's |
| documentation</a>). Note also that the push interface can belimited to SAX: |
| just use the two first arguments of<code>xmlCreatePushParserCtxt()</code>.</p><h3><a name="Building" id="Building">Building a tree from scratch</a></h3><p>The other way to get an XML tree in memory is by building it. |
| Basicallythere is a set of functions dedicated to building new elements. |
| (These arealso described in <libxml/tree.h>.) For example, here is a |
| piece ofcode that produces the XML document used in the previous examples:</p><pre> #include <libxml/tree.h> |
| xmlDocPtr doc; |
| xmlNodePtr tree, subtree; |
| |
| doc = xmlNewDoc("1.0"); |
| doc->children = xmlNewDocNode(doc, NULL, "EXAMPLE", NULL); |
| xmlSetProp(doc->children, "prop1", "gnome is great"); |
| xmlSetProp(doc->children, "prop2", "& linux too"); |
| tree = xmlNewChild(doc->children, NULL, "head", NULL); |
| subtree = xmlNewChild(tree, NULL, "title", "Welcome to Gnome"); |
| tree = xmlNewChild(doc->children, NULL, "chapter", NULL); |
| subtree = xmlNewChild(tree, NULL, "title", "The Linux adventure"); |
| subtree = xmlNewChild(tree, NULL, "p", "bla bla bla ..."); |
| subtree = xmlNewChild(tree, NULL, "image", NULL); |
| xmlSetProp(subtree, "href", "linus.gif");</pre><p>Not really rocket science ...</p><h3><a name="Traversing" id="Traversing">Traversing the tree</a></h3><p>Basically by <a href="html/libxml-tree.html">including |
| "tree.h"</a>yourcode has access to the internal structure of all the elements |
| of the tree.The names should be somewhat simple like |
| <strong>parent</strong>,<strong>children</strong>, <strong>next</strong>, |
| <strong>prev</strong>,<strong>properties</strong>, etc... For example, still |
| with the previousexample:</p><pre><code>doc->children->children->children</code></pre><p>points to the title element,</p><pre>doc->children->children->next->children->children</pre><p>points to the text node containing the chapter title "The |
| Linuxadventure".</p><p><strong>NOTE</strong>: XML allows <em>PI</em>s and <em>comments</em>to |
| bepresent before the document root, so <code>doc->children</code>may |
| pointto an element which is not the document Root Element; a |
| function<code>xmlDocGetRootElement()</code>was added for this purpose.</p><h3><a name="Modifying" id="Modifying">Modifying the tree</a></h3><p>Functions are provided for reading and writing the document content. |
| Hereis an excerpt from the <a href="html/libxml-tree.html">tree API</a>:</p><dl><dt><code>xmlAttrPtr xmlSetProp(xmlNodePtr node, const xmlChar *name, |
| constxmlChar *value);</code></dt> |
| <dd><p>This sets (or changes) an attribute carried by an ELEMENT node.The |
| value can be NULL.</p> |
| </dd> |
| </dl><dl><dt><code>const xmlChar *xmlGetProp(xmlNodePtr node, const |
| xmlChar*name);</code></dt> |
| <dd><p>This function returns a pointer to new copy of the |
| propertycontent. Note that the user must deallocate the result.</p> |
| </dd> |
| </dl><p>Two functions are provided for reading and writing the text associatedwith |
| elements:</p><dl><dt><code>xmlNodePtr xmlStringGetNodeList(xmlDocPtr doc, const |
| xmlChar*value);</code></dt> |
| <dd><p>This function takes an "external" string and converts it to |
| onetext node or possibly to a list of entity and text nodes. |
| Allnon-predefined entity references like &Gnome; will be |
| storedinternally as entity nodes, hence the result of the function may |
| not bea single node.</p> |
| </dd> |
| </dl><dl><dt><code>xmlChar *xmlNodeListGetString(xmlDocPtr doc, xmlNodePtr list, |
| intinLine);</code></dt> |
| <dd><p>This function is the inverse |
| of<code>xmlStringGetNodeList()</code>. It generates a new |
| stringcontaining the content of the text and entity nodes. Note the |
| extraargument inLine. If this argument is set to 1, the function will |
| expandentity references. For example, instead of returning the |
| &Gnome;XML encoding in the string, it will substitute it with its |
| value (say,"GNU Network Object Model Environment").</p> |
| </dd> |
| </dl><h3><a name="Saving" id="Saving">Saving a tree</a></h3><p>Basically 3 options are possible:</p><dl><dt><code>void xmlDocDumpMemory(xmlDocPtr cur, xmlChar**mem, |
| int*size);</code></dt> |
| <dd><p>Returns a buffer into which the document has been saved.</p> |
| </dd> |
| </dl><dl><dt><code>extern void xmlDocDump(FILE *f, xmlDocPtr doc);</code></dt> |
| <dd><p>Dumps a document to an open file descriptor.</p> |
| </dd> |
| </dl><dl><dt><code>int xmlSaveFile(const char *filename, xmlDocPtr cur);</code></dt> |
| <dd><p>Saves the document to a file. In this case, the |
| compressioninterface is triggered if it has been turned on.</p> |
| </dd> |
| </dl><h3><a name="Compressio" id="Compressio">Compression</a></h3><p>The library transparently handles compression when doing |
| file-basedaccesses. The level of compression on saves can be turned on either |
| globallyor individually for one file:</p><dl><dt><code>int xmlGetDocCompressMode (xmlDocPtr doc);</code></dt> |
| <dd><p>Gets the document compression ratio (0-9).</p> |
| </dd> |
| </dl><dl><dt><code>void xmlSetDocCompressMode (xmlDocPtr doc, int mode);</code></dt> |
| <dd><p>Sets the document compression ratio.</p> |
| </dd> |
| </dl><dl><dt><code>int xmlGetCompressMode(void);</code></dt> |
| <dd><p>Gets the default compression ratio.</p> |
| </dd> |
| </dl><dl><dt><code>void xmlSetCompressMode(int mode);</code></dt> |
| <dd><p>Sets the default compression ratio.</p> |
| </dd> |
| </dl><p><a href="bugs.html">Daniel Veillard</a></p></td></tr></table></td></tr></table></td></tr></table></td></tr></table></td></tr></table></body></html> |