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| 10 | </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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href="ftp://xmlsoft.org/">FTP</a></li><li><a href="http://www.zlatkovic.com/projects/libxml/">Windows binaries</a></li><li><a href="http://opencsw.org/packages/libxml2">Solaris binaries</a></li><li><a href="http://www.explain.com.au/oss/libxml2xslt.html">MacOsX binaries</a></li><li><a href="http://lxml.de/">lxml Python bindings</a></li><li><a href="http://cpan.uwinnipeg.ca/dist/XML-LibXML">Perl bindings</a></li><li><a href="http://libxmlplusplus.sourceforge.net/">C++ bindings</a></li><li><a href="http://www.zend.com/php5/articles/php5-xmlphp.php#Heading4">PHP bindings</a></li><li><a href="http://sourceforge.net/projects/libxml2-pas/">Pascal bindings</a></li><li><a href="http://libxml.rubyforge.org/">Ruby bindings</a></li><li><a href="http://tclxml.sourceforge.net/">Tcl bindings</a></li><li><a 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
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| 11 | using the XML tollkit from the C language. It is not intended to be
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| 12 | extensive. I hope the automatically generated documents will provide the
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| 13 | completeness required, but as a separate set of documents. The interfaces of
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| 14 | the XML parser are by principle low level, Those interested in a higher level
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| 15 | API should <a href="#DOM">look at DOM</a>.</p><p>The <a href="html/libxml-parser.html">parser interfaces for XML</a> are
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| 16 | separated from the <a href="html/libxml-htmlparser.html">HTML parser
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| 17 | interfaces</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
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| 18 | documents either from in-memory strings or from files. The functions are
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| 19 | defined in "parser.h":</p><dl>
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| 20 | <dt><code>xmlDocPtr xmlParseMemory(char *buffer, int size);</code></dt>
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| 21 | <dd><p>Parse a null-terminated string containing the document.</p>
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| 22 | </dd>
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| 23 | </dl><dl>
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| 24 | <dt><code>xmlDocPtr xmlParseFile(const char *filename);</code></dt>
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| 25 | <dd><p>Parse an XML document contained in a (possibly compressed)
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| 26 | file.</p>
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| 27 | </dd>
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| 28 | </dl><p>The parser returns a pointer to the document structure (or NULL in case of
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| 29 | failure).</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
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| 30 | being fetched (which is common for GUI based programs) libxml2 provides a
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| 31 | push interface, too, as of version 1.8.3. Here are the interface
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| 32 | functions:</p><pre>xmlParserCtxtPtr xmlCreatePushParserCtxt(xmlSAXHandlerPtr sax,
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| 33 | void *user_data,
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| 34 | const char *chunk,
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| 35 | int size,
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| 36 | const char *filename);
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| 37 | int xmlParseChunk (xmlParserCtxtPtr ctxt,
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| 38 | const char *chunk,
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| 39 | int size,
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| 40 | int terminate);</pre><p>and here is a simple example showing how to use the interface:</p><pre> FILE *f;
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| 41 |
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| 42 | f = fopen(filename, "r");
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| 43 | if (f != NULL) {
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| 44 | int res, size = 1024;
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| 45 | char chars[1024];
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| 46 | xmlParserCtxtPtr ctxt;
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| 47 |
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| 48 | res = fread(chars, 1, 4, f);
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| 49 | if (res > 0) {
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| 50 | ctxt = xmlCreatePushParserCtxt(NULL, NULL,
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| 51 | chars, res, filename);
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| 52 | while ((res = fread(chars, 1, size, f)) > 0) {
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| 53 | xmlParseChunk(ctxt, chars, res, 0);
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| 54 | }
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| 55 | xmlParseChunk(ctxt, chars, 0, 1);
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| 56 | doc = ctxt->myDoc;
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| 57 | xmlFreeParserCtxt(ctxt);
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| 58 | }
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| 59 | }</pre><p>The HTML parser embedded into libxml2 also has a push interface; the
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| 60 | functions 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
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| 61 | the document in memory and then building the tree itself. Reading a document
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| 62 | without building the tree is possible using the SAX interfaces (see SAX.h and
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| 63 | <a href="http://www.daa.com.au/~james/gnome/xml-sax/xml-sax.html">James
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| 64 | Henstridge's documentation</a>). Note also that the push interface can be
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| 65 | limited to SAX: just use the two first arguments of
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| 66 | <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
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| 67 | there is a set of functions dedicated to building new elements. (These are
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| 68 | also described in <libxml/tree.h>.) For example, here is a piece of
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| 69 | code that produces the XML document used in the previous examples:</p><pre> #include <libxml/tree.h>
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| 70 | xmlDocPtr doc;
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| 71 | xmlNodePtr tree, subtree;
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| 72 |
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| 73 | doc = xmlNewDoc("1.0");
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| 74 | doc->children = xmlNewDocNode(doc, NULL, "EXAMPLE", NULL);
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| 75 | xmlSetProp(doc->children, "prop1", "gnome is great");
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| 76 | xmlSetProp(doc->children, "prop2", "& linux too");
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| 77 | tree = xmlNewChild(doc->children, NULL, "head", NULL);
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| 78 | subtree = xmlNewChild(tree, NULL, "title", "Welcome to Gnome");
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| 79 | tree = xmlNewChild(doc->children, NULL, "chapter", NULL);
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| 80 | subtree = xmlNewChild(tree, NULL, "title", "The Linux adventure");
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| 81 | subtree = xmlNewChild(tree, NULL, "p", "bla bla bla ...");
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| 82 | subtree = xmlNewChild(tree, NULL, "image", NULL);
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| 83 | 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
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| 84 | code has access to the internal structure of all the elements of the tree.
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| 85 | The names should be somewhat simple like <strong>parent</strong>,
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| 86 | <strong>children</strong>, <strong>next</strong>, <strong>prev</strong>,
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| 87 | <strong>properties</strong>, etc... For example, still with the previous
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| 88 | example:</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
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| 89 | adventure".</p><p><strong>NOTE</strong>: XML allows <em>PI</em>s and <em>comments</em> to be
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| 90 | present before the document root, so <code>doc->children</code> may point
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| 91 | to an element which is not the document Root Element; a function
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| 92 | <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
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| 93 | is an excerpt from the <a href="html/libxml-tree.html">tree API</a>:</p><dl>
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| 94 | <dt><code>xmlAttrPtr xmlSetProp(xmlNodePtr node, const xmlChar *name, const
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| 95 | xmlChar *value);</code></dt>
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| 96 | <dd><p>This sets (or changes) an attribute carried by an ELEMENT node.
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| 97 | The value can be NULL.</p>
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| 98 | </dd>
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| 99 | </dl><dl>
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| 100 | <dt><code>const xmlChar *xmlGetProp(xmlNodePtr node, const xmlChar
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| 101 | *name);</code></dt>
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| 102 | <dd><p>This function returns a pointer to new copy of the property
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| 103 | content. Note that the user must deallocate the result.</p>
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| 104 | </dd>
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| 105 | </dl><p>Two functions are provided for reading and writing the text associated
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| 106 | with elements:</p><dl>
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| 107 | <dt><code>xmlNodePtr xmlStringGetNodeList(xmlDocPtr doc, const xmlChar
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| 108 | *value);</code></dt>
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| 109 | <dd><p>This function takes an "external" string and converts it to one
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| 110 | text node or possibly to a list of entity and text nodes. All
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| 111 | non-predefined entity references like &Gnome; will be stored
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| 112 | internally as entity nodes, hence the result of the function may not be
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| 113 | a single node.</p>
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| 114 | </dd>
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| 115 | </dl><dl>
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| 116 | <dt><code>xmlChar *xmlNodeListGetString(xmlDocPtr doc, xmlNodePtr list, int
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| 117 | inLine);</code></dt>
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| 118 | <dd><p>This function is the inverse of
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| 119 | <code>xmlStringGetNodeList()</code>. It generates a new string
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| 120 | containing the content of the text and entity nodes. Note the extra
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| 121 | argument inLine. If this argument is set to 1, the function will expand
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| 122 | entity references. For example, instead of returning the &Gnome;
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| 123 | XML encoding in the string, it will substitute it with its value (say,
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| 124 | "GNU Network Object Model Environment").</p>
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| 125 | </dd>
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| 126 | </dl><h3><a name="Saving" id="Saving">Saving a tree</a></h3><p>Basically 3 options are possible:</p><dl>
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| 127 | <dt><code>void xmlDocDumpMemory(xmlDocPtr cur, xmlChar**mem, int
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| 128 | *size);</code></dt>
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| 129 | <dd><p>Returns a buffer into which the document has been saved.</p>
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| 130 | </dd>
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| 131 | </dl><dl>
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| 132 | <dt><code>extern void xmlDocDump(FILE *f, xmlDocPtr doc);</code></dt>
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| 133 | <dd><p>Dumps a document to an open file descriptor.</p>
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| 134 | </dd>
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| 135 | </dl><dl>
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| 136 | <dt><code>int xmlSaveFile(const char *filename, xmlDocPtr cur);</code></dt>
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| 137 | <dd><p>Saves the document to a file. In this case, the compression
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| 138 | interface is triggered if it has been turned on.</p>
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| 139 | </dd>
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| 140 | </dl><h3><a name="Compressio" id="Compressio">Compression</a></h3><p>The library transparently handles compression when doing file-based
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| 141 | accesses. The level of compression on saves can be turned on either globally
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| 142 | or individually for one file:</p><dl>
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| 143 | <dt><code>int xmlGetDocCompressMode (xmlDocPtr doc);</code></dt>
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| 144 | <dd><p>Gets the document compression ratio (0-9).</p>
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| 145 | </dd>
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| 146 | </dl><dl>
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| 147 | <dt><code>void xmlSetDocCompressMode (xmlDocPtr doc, int mode);</code></dt>
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| 148 | <dd><p>Sets the document compression ratio.</p>
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| 149 | </dd>
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| 150 | </dl><dl>
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| 151 | <dt><code>int xmlGetCompressMode(void);</code></dt>
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| 152 | <dd><p>Gets the default compression ratio.</p>
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| 153 | </dd>
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| 154 | </dl><dl>
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| 155 | <dt><code>void xmlSetCompressMode(int mode);</code></dt>
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| 156 | <dd><p>Sets the default compression ratio.</p>
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| 157 | </dd>
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| 158 | </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>
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