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1<?xml version="1.0" encoding="ISO-8859-1"?> 2<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> 3<html xmlns="http://www.w3.org/1999/xhtml"><head><meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1" /><link rel="SHORTCUT ICON" href="/favicon.ico" /><style type="text/css"> 4TD {font-family: Verdana,Arial,Helvetica} 5BODY {font-family: Verdana,Arial,Helvetica; margin-top: 2em; margin-left: 0em; margin-right: 0em} 6H1 {font-family: Verdana,Arial,Helvetica} 7H2 {font-family: Verdana,Arial,Helvetica} 8H3 {font-family: Verdana,Arial,Helvetica} 9A:link, A:visited, A:active { text-decoration: underline } 10</style><title>The parser interfaces</title></head><body bgcolor="#8b7765" text="#000000" link="#a06060" vlink="#a06060"><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 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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="examples/index.html" style="font-weight:bold">Code Examples</a></li><li><a href="guidelines.html">XML Guidelines</a></li><li><a href="tutorial/index.html">Tutorial</a></li><li><a href="xmlreader.html">The Reader Interface</a></li><li><a href="ChangeLog.html">ChangeLog</a></li><li><a href="XSLT.html">XSLT</a></li><li><a href="python.html">Python and bindings</a></li><li><a href="architecture.html">libxml2 architecture</a></li><li><a href="tree.html">The tree 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href="http://bugzilla.gnome.org/buglist.cgi?product=libxml2">Bug Tracker</a></li></ul></td></tr></table></td></tr></table></td><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"><p>This section is directly intended to help programmers getting bootstrapped 11using the XML tollkit from the C language. It is not intended to be 12extensive. I hope the automatically generated documents will provide the 13completeness required, but as a separate set of documents. The interfaces of 14the XML parser are by principle low level, Those interested in a higher level 15API should <a href="#DOM">look at DOM</a>.</p><p>The <a href="html/libxml-parser.html">parser interfaces for XML</a> are 16separated from the <a href="html/libxml-htmlparser.html">HTML parser 17interfaces</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 accepts 18documents either from in-memory strings or from files. The functions are 19defined in "parser.h":</p><dl><dt><code>xmlDocPtr xmlParseMemory(char *buffer, int size);</code></dt> 20 <dd><p>Parse a null-terminated string containing the document.</p> 21 </dd> 22</dl><dl><dt><code>xmlDocPtr xmlParseFile(const char *filename);</code></dt> 23 <dd><p>Parse an XML document contained in a (possibly compressed) 24 file.</p> 25 </dd> 26</dl><p>The parser returns a pointer to the document structure (or NULL in case of 27failure).</p><h3 id="Invoking1">Invoking the parser: the push method</h3><p>In order for the application to keep the control when the document is 28being fetched (which is common for GUI based programs) libxml2 provides a 29push interface, too, as of version 1.8.3. Here are the interface 30functions:</p><pre>xmlParserCtxtPtr xmlCreatePushParserCtxt(xmlSAXHandlerPtr sax, 31 void *user_data, 32 const char *chunk, 33 int size, 34 const char *filename); 35int xmlParseChunk (xmlParserCtxtPtr ctxt, 36 const char *chunk, 37 int size, 38 int terminate);</pre><p>and here is a simple example showing how to use the interface:</p><pre> FILE *f; 39 40 f = fopen(filename, "r"); 41 if (f != NULL) { 42 int res, size = 1024; 43 char chars[1024]; 44 xmlParserCtxtPtr ctxt; 45 46 res = fread(chars, 1, 4, f); 47 if (res > 0) { 48 ctxt = xmlCreatePushParserCtxt(NULL, NULL, 49 chars, res, filename); 50 while ((res = fread(chars, 1, size, f)) > 0) { 51 xmlParseChunk(ctxt, chars, res, 0); 52 } 53 xmlParseChunk(ctxt, chars, 0, 1); 54 doc = ctxt->myDoc; 55 xmlFreeParserCtxt(ctxt); 56 } 57 }</pre><p>The HTML parser embedded into libxml2 also has a push interface; the 58functions 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 loading 59the document in memory and then building the tree itself. Reading a document 60without building the tree is possible using the SAX interfaces (see SAX.h and 61<a href="http://www.daa.com.au/~james/gnome/xml-sax/xml-sax.html">James 62Henstridge's documentation</a>). Note also that the push interface can be 63limited to SAX: just use the two first arguments of 64<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. Basically 65there is a set of functions dedicated to building new elements. (These are 66also described in <libxml/tree.h>.) For example, here is a piece of 67code that produces the XML document used in the previous examples:</p><pre> #include <libxml/tree.h> 68 xmlDocPtr doc; 69 xmlNodePtr tree, subtree; 70 71 doc = xmlNewDoc("1.0"); 72 doc->children = xmlNewDocNode(doc, NULL, "EXAMPLE", NULL); 73 xmlSetProp(doc->children, "prop1", "gnome is great"); 74 xmlSetProp(doc->children, "prop2", "& linux too"); 75 tree = xmlNewChild(doc->children, NULL, "head", NULL); 76 subtree = xmlNewChild(tree, NULL, "title", "Welcome to Gnome"); 77 tree = xmlNewChild(doc->children, NULL, "chapter", NULL); 78 subtree = xmlNewChild(tree, NULL, "title", "The Linux adventure"); 79 subtree = xmlNewChild(tree, NULL, "p", "bla bla bla ..."); 80 subtree = xmlNewChild(tree, NULL, "image", NULL); 81 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> your 82code has access to the internal structure of all the elements of the tree. 83The names should be somewhat simple like <strong>parent</strong>, 84<strong>children</strong>, <strong>next</strong>, <strong>prev</strong>, 85<strong>properties</strong>, etc... For example, still with the previous 86example:</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 Linux 87adventure".</p><p><strong>NOTE</strong>: XML allows <em>PI</em>s and <em>comments</em> to be 88present before the document root, so <code>doc->children</code> may point 89to an element which is not the document Root Element; a function 90<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. Here 91is an excerpt from the <a href="html/libxml-tree.html">tree API</a>:</p><dl><dt><code>xmlAttrPtr xmlSetProp(xmlNodePtr node, const xmlChar *name, const 92 xmlChar *value);</code></dt> 93 <dd><p>This sets (or changes) an attribute carried by an ELEMENT node. 94 The value can be NULL.</p> 95 </dd> 96</dl><dl><dt><code>const xmlChar *xmlGetProp(xmlNodePtr node, const xmlChar 97 *name);</code></dt> 98 <dd><p>This function returns a pointer to new copy of the property 99 content. Note that the user must deallocate the result.</p> 100 </dd> 101</dl><p>Two functions are provided for reading and writing the text associated 102with elements:</p><dl><dt><code>xmlNodePtr xmlStringGetNodeList(xmlDocPtr doc, const xmlChar 103 *value);</code></dt> 104 <dd><p>This function takes an "external" string and converts it to one 105 text node or possibly to a list of entity and text nodes. All 106 non-predefined entity references like &Gnome; will be stored 107 internally as entity nodes, hence the result of the function may not be 108 a single node.</p> 109 </dd> 110</dl><dl><dt><code>xmlChar *xmlNodeListGetString(xmlDocPtr doc, xmlNodePtr list, int 111 inLine);</code></dt> 112 <dd><p>This function is the inverse of 113 <code>xmlStringGetNodeList()</code>. It generates a new string 114 containing the content of the text and entity nodes. Note the extra 115 argument inLine. If this argument is set to 1, the function will expand 116 entity references. For example, instead of returning the &Gnome; 117 XML encoding in the string, it will substitute it with its value (say, 118 "GNU Network Object Model Environment").</p> 119 </dd> 120</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 121 *size);</code></dt> 122 <dd><p>Returns a buffer into which the document has been saved.</p> 123 </dd> 124</dl><dl><dt><code>extern void xmlDocDump(FILE *f, xmlDocPtr doc);</code></dt> 125 <dd><p>Dumps a document to an open file descriptor.</p> 126 </dd> 127</dl><dl><dt><code>int xmlSaveFile(const char *filename, xmlDocPtr cur);</code></dt> 128 <dd><p>Saves the document to a file. In this case, the compression 129 interface is triggered if it has been turned on.</p> 130 </dd> 131</dl><h3><a name="Compressio" id="Compressio">Compression</a></h3><p>The library transparently handles compression when doing file-based 132accesses. The level of compression on saves can be turned on either globally 133or individually for one file:</p><dl><dt><code>int xmlGetDocCompressMode (xmlDocPtr doc);</code></dt> 134 <dd><p>Gets the document compression ratio (0-9).</p> 135 </dd> 136</dl><dl><dt><code>void xmlSetDocCompressMode (xmlDocPtr doc, int mode);</code></dt> 137 <dd><p>Sets the document compression ratio.</p> 138 </dd> 139</dl><dl><dt><code>int xmlGetCompressMode(void);</code></dt> 140 <dd><p>Gets the default compression ratio.</p> 141 </dd> 142</dl><dl><dt><code>void xmlSetCompressMode(int mode);</code></dt> 143 <dd><p>Sets the default compression ratio.</p> 144 </dd> 145</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> 146
