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591 lines
19 KiB
HTML
591 lines
19 KiB
HTML
<html>
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<body>
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<h1 align='right'><a name='BASICS'>Chapter 2 - Getting Started
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with Mini-XML</a></h1>
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<p>This chapter describes how to write programs that use Mini-XML to
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access data in an XML file. Mini-XML provides the following
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functionality:</p>
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<ul>
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<li>Reading of UTF-8 and UTF-16 and writing of UTF-8 encoded XML files and strings.</li>
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<li>Data is stored in a linked-list tree structure, preserving the XML data hierarchy.</li>
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<li>SAX (streamed) reading of XML files and strings to minimize memory usage.</li>
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<li>Supports arbitrary element names, attributes, and attribute values with no preset limits, just available memory.</li>
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<li>Supports integer, real, opaque ("cdata"), and text data types in "leaf" nodes.</li>
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<li>Functions for creating and managing trees of data.</li>
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<li>"Find" and "walk" functions for easily locating and navigating trees of data.</li>
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</ul>
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<p>Mini-XML doesn't do validation or other types of processing on the data based upon schema files or other sources of definition information.</p>
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<h2>The Basics</h2>
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<p>Mini-XML provides a single header file which you include:</p>
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<pre>
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#include <mxml.h>
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</pre>
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<p>The Mini-XML library is included with your program using the
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<kbd>-lmxml</kbd> option:</p>
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<pre>
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<kbd>gcc -o myprogram myprogram.c -lmxml ENTER</kbd>
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</pre>
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<p>If you have the <tt>pkg-config(1)</tt> software installed,
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you can use it to determine the proper compiler and linker options
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for your installation:</p>
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<pre>
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<kbd>pkg-config --cflags mxml ENTER</kbd>
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<kbd>pkg-config --libs mxml ENTER</kbd>
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</pre>
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<h2>Nodes</h2>
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<p>Every piece of information in an XML file is stored in memory in "nodes".
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Nodes are defined by the <a href='#mxml_node_t'><tt>mxml_node_t</tt></a>
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structure. Each node has a typed value, optional user data, a parent node,
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sibling nodes (previous and next), and potentially child nodes.</p>
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<p>For example, if you have an XML file like the following:</p>
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<pre>
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<?xml version="1.0" encoding="utf-8"?>
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<data>
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<node>val1</node>
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<node>val2</node>
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<node>val3</node>
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<group>
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<node>val4</node>
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<node>val5</node>
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<node>val6</node>
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</group>
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<node>val7</node>
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<node>val8</node>
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</data>
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</pre>
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<p>the node tree for the file would look like the following in memory:</p>
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<pre>
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?xml version="1.0" encoding="utf-8"?
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data
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node - node - node - group - node - node
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| | | | | |
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val1 val2 val3 | val7 val8
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node - node - node
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| | |
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val4 val5 val6
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</pre>
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<p>where "-" is a pointer to the sibling node and "|" is a pointer
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to the first child or parent node.</p>
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<p>The <a href="#mxmlGetType"><tt>mxmlGetType</tt></a> function gets the type of
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a node, one of <tt>MXML_CUSTOM</tt>, <tt>MXML_ELEMENT</tt>,
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<tt>MXML_INTEGER</tt>, <tt>MXML_OPAQUE</tt>, <tt>MXML_REAL</tt>, or
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<tt>MXML_TEXT</tt>. The parent and sibling nodes are accessed using the
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<a href="#mxmlGetParent"><tt>mxmlGetParent</tt></a>,
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<a href="#mxmlGetNext"><tt>mxmlGetNext</tt></a>, and
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<a href="#mxmlGetPrevious"><tt>mxmlGetPrevious</tt></a> functions. The
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<a href="#mxmlGetUserData"><tt>mxmlGetUserData</tt></a> function gets any user
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data associated with the node.</p>
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<h3>CDATA Nodes</h3>
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<p>CDATA (<tt>MXML_ELEMENT</tt>) nodes are created using the
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<a href="#mxmlNewCDATA"><tt>mxmlNewCDATA</tt></a> function. The
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<a href="#mxmlGetCDATA"><tt>mxmlGetCDATA</tt></a> function retrieves the
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CDATA string pointer for a node.</p>
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<blockquote><b>Note:</b>
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<p>CDATA nodes are currently stored in memory as special elements. This will
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be changed in a future major release of Mini-XML.</p>
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</blockquote>
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<h3>Custom Nodes</h3>
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<p>Custom (<tt>MXML_CUSTOM</tt>) nodes are created using the
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<a href="#mxmlNewCustom"><tt>mxmlNewCustom</tt></a> function or using a custom
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load callback specified using the
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<a href="#mxmlSetCustomHandlers"><tt>mxmlSetCustomHandlers</tt></a> function.
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The <a href="#mxmlGetCustom"><tt>mxmlGetCustom</tt></a> function retrieves the
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custom value pointer for a node.</p>
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<h3>Comment Nodes</h3>
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<p>Comment (<tt>MXML_ELEMENT</tt>) nodes are created using the
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<a href="#mxmlNewElement"><tt>mxmlNewElement</tt></a> function. The
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<a href="#mxmlGetElement"><tt>mxmlGetElement</tt></a> function retrieves the
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comment string pointer for a node, including the surrounding "!--" and "--"
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characters.</p>
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<blockquote><b>Note:</b>
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<p>Comment nodes are currently stored in memory as special elements. This will
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be changed in a future major release of Mini-XML.</p>
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</blockquote>
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<h3>Element Nodes</h3>
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<p>Element (<tt>MXML_ELEMENT</tt>) nodes are created using the
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<a href="#mxmlNewElement"><tt>mxmlNewElement</tt></a> function. The
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<a href="#mxmlGetElement"><tt>mxmlGetElement</tt></a> function retrieves the
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element name, the
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<a href="#mxmlElementGetAttr"><tt>mxmlElementGetAttr</tt></a> function retrieves
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the value string for a named attribute associated with the element, and the
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<a href="#mxmlGetFirstChild"><tt>mxmlGetFirstChild</tt></a> and
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<a href="#mxmlGetLastChild"><tt>mxmlGetLastChild</tt></a> functions retrieve the
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first and last child nodes for the element, respectively.</p>
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<h3>Integer Nodes</h3>
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<p>Integer (<tt>MXML_INTEGER</tt>) nodes are created using the
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<a href="#mxmlNewInteger"><tt>mxmlNewInteger</tt></a> function. The
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<a href="#mxmlGetInteger"><tt>mxmlGetInteger</tt></a> function retrieves the
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integer value for a node.</p>
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<h3>Opaque Nodes</h3>
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<p>Opaque (<tt>MXML_OPAQUE</tt>) nodes are created using the
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<a href="#mxmlNewOpaque"><tt>mxmlNewOpaque</tt></a> function. The
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<a href="#mxmlGetOpaque"><tt>mxmlGetOpaque</tt></a> function retrieves the
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opaque string pointer for a node. Opaque nodes are like string nodes but
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preserve all whitespace between nodes.</p>
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<h3>Text Nodes</h3>
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<p>Text (<tt>MXML_TEXT</tt>) nodes are created using the
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<a href="#mxmlNewText"><tt>mxmlNewText</tt></a> and
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<a href="#mxmlNewTextf"><tt>mxmlNewTextf</tt></a> functions. Each text node
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consists of a text string and (leading) whitespace value - the
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<a href="#mxmlGetText"><tt>mxmlGetText</tt></a> function retrieves the
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text string pointer and whitespace value for a node.</p>
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<!-- NEED 12 -->
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<h3>Processing Instruction Nodes</h3>
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<p>Processing instruction (<tt>MXML_ELEMENT</tt>) nodes are created using the
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<a href="#mxmlNewElement"><tt>mxmlNewElement</tt></a> function. The
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<a href="#mxmlGetElement"><tt>mxmlGetElement</tt></a> function retrieves the
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processing instruction string for a node, including the surrounding "?"
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characters.</p>
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<blockquote><b>Note:</b>
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<p>Processing instruction nodes are currently stored in memory as special
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elements. This will be changed in a future major release of Mini-XML.</p>
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</blockquote>
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<h3>Real Number Nodes</h3>
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<p>Real number (<tt>MXML_REAL</tt>) nodes are created using the
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<a href="#mxmlNewReal"><tt>mxmlNewReal</tt></a> function. The
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<a href="#mxmlGetReal"><tt>mxmlGetReal</tt></a> function retrieves the
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CDATA string pointer for a node.</p>
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<!-- NEED 15 -->
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<h3>XML Declaration Nodes</h3>
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<p>XML declaration (<tt>MXML_ELEMENT</tt>) nodes are created using the
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<a href="#mxmlNewXML"><tt>mxmlNewXML</tt></a> function. The
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<a href="#mxmlGetElement"><tt>mxmlGetElement</tt></a> function retrieves the
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XML declaration string for a node, including the surrounding "?" characters.</p>
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<blockquote><b>Note:</b>
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<p>XML declaration nodes are currently stored in memory as special elements.
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This will be changed in a future major release of Mini-XML.</p>
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</blockquote>
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<!-- NEW PAGE -->
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<h2>Creating XML Documents</h2>
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<p>You can create and update XML documents in memory using the
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various <tt>mxmlNew</tt> functions. The following code will
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create the XML document described in the previous section:</p>
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<pre>
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mxml_node_t *xml; /* <?xml ... ?> */
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mxml_node_t *data; /* <data> */
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mxml_node_t *node; /* <node> */
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mxml_node_t *group; /* <group> */
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xml = mxmlNewXML("1.0");
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data = mxmlNewElement(xml, "data");
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node = mxmlNewElement(data, "node");
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mxmlNewText(node, 0, "val1");
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node = mxmlNewElement(data, "node");
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mxmlNewText(node, 0, "val2");
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node = mxmlNewElement(data, "node");
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mxmlNewText(node, 0, "val3");
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group = mxmlNewElement(data, "group");
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node = mxmlNewElement(group, "node");
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mxmlNewText(node, 0, "val4");
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node = mxmlNewElement(group, "node");
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mxmlNewText(node, 0, "val5");
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node = mxmlNewElement(group, "node");
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mxmlNewText(node, 0, "val6");
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node = mxmlNewElement(data, "node");
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mxmlNewText(node, 0, "val7");
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node = mxmlNewElement(data, "node");
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mxmlNewText(node, 0, "val8");
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</pre>
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<!-- NEED 6 -->
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<p>We start by creating the declaration node common to all XML files using the
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<a href="#mxmlNewXML"><tt>mxmlNewXML</tt></a> function:</p>
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<pre>
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xml = mxmlNewXML("1.0");
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</pre>
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<p>We then create the <tt><data></tt> node used for this document using
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the <a href="#mxmlNewElement"><tt>mxmlNewElement</tt></a> function. The first
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argument specifies the parent node (<tt>xml</tt>) while the second specifies the
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element name (<tt>data</tt>):</p>
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<pre>
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data = mxmlNewElement(xml, "data");
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</pre>
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<p>Each <tt><node>...</node></tt> in the file is created using the
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<tt>mxmlNewElement</tt> and <a href="#mxmlNewText"><tt>mxmlNewText</tt></a>
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functions. The first argument of <tt>mxmlNewText</tt> specifies the parent node
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(<tt>node</tt>). The second argument specifies whether whitespace appears before
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the text - 0 or false in this case. The last argument specifies the actual text
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to add:</p>
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<pre>
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node = mxmlNewElement(data, "node");
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mxmlNewText(node, 0, "val1");
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</pre>
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<p>The resulting in-memory XML document can then be saved or processed just like
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one loaded from disk or a string.</p>
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<!-- NEED 15 -->
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<h2>Loading XML</h2>
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<p>You load an XML file using the <a
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href='#mxmlLoadFile'><tt>mxmlLoadFile</tt></a>
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function:</p>
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<pre>
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FILE *fp;
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mxml_node_t *tree;
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fp = fopen("filename.xml", "r");
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tree = mxmlLoadFile(NULL, fp,
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MXML_TEXT_CALLBACK);
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fclose(fp);
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</pre>
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<p>The first argument specifies an existing XML parent node, if
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any. Normally you will pass <tt>NULL</tt> for this argument
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unless you are combining multiple XML sources. The XML file must
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contain a complete XML document including the <tt>?xml</tt>
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element if the parent node is <tt>NULL</tt>.</p>
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<p>The second argument specifies the stdio file to read from, as
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opened by <tt>fopen()</tt> or <tt>popen()</tt>. You can also use
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<tt>stdin</tt> if you are implementing an XML filter
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program.</p>
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<p>The third argument specifies a callback function which returns
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the value type of the immediate children for a new element node:
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<tt>MXML_CUSTOM</tt>, <tt>MXML_IGNORE</tt>,
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<tt>MXML_INTEGER</tt>, <tt>MXML_OPAQUE</tt>, <tt>MXML_REAL</tt>,
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or <tt>MXML_TEXT</tt>. Load callbacks are described in detail in
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<a href='#LOAD_CALLBACKS'>Chapter 3</a>. The example code uses
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the <tt>MXML_TEXT_CALLBACK</tt> constant which specifies that all
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data nodes in the document contain whitespace-separated text
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values. Other standard callbacks include
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<tt>MXML_IGNORE_CALLBACK</tt>, <tt>MXML_INTEGER_CALLBACK</tt>,
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<tt>MXML_OPAQUE_CALLBACK</tt>, and
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<tt>MXML_REAL_CALLBACK</tt>.</p>
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<p>The <a href='#mxmlLoadString'><tt>mxmlLoadString</tt></a>
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function loads XML node trees from a string:</p>
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<!-- NEED 10 -->
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<pre>
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char buffer[8192];
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mxml_node_t *tree;
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...
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tree = mxmlLoadString(NULL, buffer,
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MXML_TEXT_CALLBACK);
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</pre>
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<p>The first and third arguments are the same as used for
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<tt>mxmlLoadFile()</tt>. The second argument specifies the
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string or character buffer to load and must be a complete XML
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document including the <tt>?xml</tt> element if the parent node
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is <tt>NULL</tt>.</p>
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<!-- NEED 15 -->
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<h2>Saving XML</h2>
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<p>You save an XML file using the <a
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href='#mxmlSaveFile'><tt>mxmlSaveFile</tt></a> function:</p>
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<pre>
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FILE *fp;
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mxml_node_t *tree;
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fp = fopen("filename.xml", "w");
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mxmlSaveFile(tree, fp, MXML_NO_CALLBACK);
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fclose(fp);
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</pre>
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<p>The first argument is the XML node tree to save. It should
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normally be a pointer to the top-level <tt>?xml</tt> node in
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your XML document.</p>
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<p>The second argument is the stdio file to write to, as opened
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by <tt>fopen()</tt> or <tt>popen()</tt>. You can also use
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<tt>stdout</tt> if you are implementing an XML filter
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program.</p>
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<p>The third argument is the whitespace callback to use when
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saving the file. Whitespace callbacks are covered in detail in <a
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href='SAVE_CALLBACKS'>Chapter 3</a>. The previous example code
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uses the <tt>MXML_NO_CALLBACK</tt> constant to specify that no
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special whitespace handling is required.</p>
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<p>The <a
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href='#mxmlSaveAllocString'><tt>mxmlSaveAllocString</tt></a>,
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and <a href='#mxmlSaveString'><tt>mxmlSaveString</tt></a>
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functions save XML node trees to strings:</p>
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<pre>
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char buffer[8192];
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char *ptr;
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mxml_node_t *tree;
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...
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mxmlSaveString(tree, buffer, sizeof(buffer),
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MXML_NO_CALLBACK);
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...
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ptr = mxmlSaveAllocString(tree, MXML_NO_CALLBACK);
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</pre>
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<p>The first and last arguments are the same as used for
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<tt>mxmlSaveFile()</tt>. The <tt>mxmlSaveString</tt> function
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takes pointer and size arguments for saving the XML document to
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a fixed-size buffer, while <tt>mxmlSaveAllocString()</tt>
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returns a string buffer that was allocated using
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<tt>malloc()</tt>.</p>
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<!-- NEED 15 -->
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<h3>Controlling Line Wrapping</h3>
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<p>When saving XML documents, Mini-XML normally wraps output
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lines at column 75 so that the text is readable in terminal
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windows. The <a
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href='#mxmlSetWrapMargin'><tt>mxmlSetWrapMargin</tt></a> function
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overrides the default wrap margin:</p>
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<pre>
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/* Set the margin to 132 columns */
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mxmlSetWrapMargin(132);
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/* Disable wrapping */
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mxmlSetWrapMargin(0);
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</pre>
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<h2>Memory Management</h2>
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<p>Once you are done with the XML data, use the <a
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href="#mxmlDelete"><tt>mxmlDelete</tt></a> function to recursively
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free the memory that is used for a particular node or the entire
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tree:</p>
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<pre>
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mxmlDelete(tree);
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</pre>
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<p>You can also use reference counting to manage memory usage. The
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<a href="#mxmlRetain"><tt>mxmlRetain</tt></a> and
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<a href="#mxmlRelease"><tt>mxmlRelease</tt></a> functions increment and
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decrement a node's use count, respectively. When the use count goes to 0,
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<tt>mxmlRelease</tt> will automatically call <tt>mxmlDelete</tt> to actually
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free the memory used by the node tree. New nodes automatically start with a
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use count of 1.</p>
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<!-- NEW PAGE-->
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<h2>Finding and Iterating Nodes</h2>
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<p>The <a
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href='#mxmlWalkPrev'><tt>mxmlWalkPrev</tt></a>
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and <a
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href='#mxmlWalkNext'><tt>mxmlWalkNext</tt></a>functions
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can be used to iterate through the XML node tree:</p>
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<pre>
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mxml_node_t *node;
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node = mxmlWalkPrev(current, tree,
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MXML_DESCEND);
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node = mxmlWalkNext(current, tree,
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MXML_DESCEND);
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</pre>
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<p>In addition, you can find a named element/node using the <a
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href='#mxmlFindElement'><tt>mxmlFindElement</tt></a>
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function:</p>
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<pre>
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mxml_node_t *node;
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node = mxmlFindElement(tree, tree, "name",
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"attr", "value",
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MXML_DESCEND);
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</pre>
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<p>The <tt>name</tt>, <tt>attr</tt>, and <tt>value</tt>
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arguments can be passed as <tt>NULL</tt> to act as wildcards,
|
|
e.g.:</p>
|
|
|
|
<!-- NEED 4 -->
|
|
<pre>
|
|
/* Find the first "a" element */
|
|
node = mxmlFindElement(tree, tree, "a",
|
|
NULL, NULL,
|
|
MXML_DESCEND);
|
|
</pre>
|
|
<!-- NEED 5 -->
|
|
<pre>
|
|
/* Find the first "a" element with "href"
|
|
attribute */
|
|
node = mxmlFindElement(tree, tree, "a",
|
|
"href", NULL,
|
|
MXML_DESCEND);
|
|
</pre>
|
|
<!-- NEED 6 -->
|
|
<pre>
|
|
/* Find the first "a" element with "href"
|
|
to a URL */
|
|
node = mxmlFindElement(tree, tree, "a",
|
|
"href",
|
|
"http://www.easysw.com/",
|
|
MXML_DESCEND);
|
|
</pre>
|
|
<!-- NEED 5 -->
|
|
<pre>
|
|
/* Find the first element with a "src"
|
|
attribute */
|
|
node = mxmlFindElement(tree, tree, NULL,
|
|
"src", NULL,
|
|
MXML_DESCEND);
|
|
</pre>
|
|
<!-- NEED 5 -->
|
|
<pre>
|
|
/* Find the first element with a "src"
|
|
= "foo.jpg" */
|
|
node = mxmlFindElement(tree, tree, NULL,
|
|
"src", "foo.jpg",
|
|
MXML_DESCEND);
|
|
</pre>
|
|
|
|
<p>You can also iterate with the same function:</p>
|
|
|
|
<pre>
|
|
mxml_node_t *node;
|
|
|
|
for (node = mxmlFindElement(tree, tree,
|
|
"name",
|
|
NULL, NULL,
|
|
MXML_DESCEND);
|
|
node != NULL;
|
|
node = mxmlFindElement(node, tree,
|
|
"name",
|
|
NULL, NULL,
|
|
MXML_DESCEND))
|
|
{
|
|
... do something ...
|
|
}
|
|
</pre>
|
|
|
|
<!-- NEED 10 -->
|
|
<p>The <tt>MXML_DESCEND</tt> argument can actually be one of
|
|
three constants:</p>
|
|
|
|
<ul>
|
|
|
|
<li><tt>MXML_NO_DESCEND</tt> means to not to look at any
|
|
child nodes in the element hierarchy, just look at
|
|
siblings at the same level or parent nodes until the top
|
|
node or top-of-tree is reached.
|
|
|
|
<p>The previous node from "group" would be the "node"
|
|
element to the left, while the next node from "group" would
|
|
be the "node" element to the right.<br><br></p></li>
|
|
|
|
<li><tt>MXML_DESCEND_FIRST</tt> means that it is OK to
|
|
descend to the first child of a node, but not to descend
|
|
further when searching. You'll normally use this when
|
|
iterating through direct children of a parent node, e.g. all
|
|
of the "node" and "group" elements under the "?xml" parent
|
|
node in the example above.
|
|
|
|
<p>This mode is only applicable to the search function; the
|
|
walk functions treat this as <tt>MXML_DESCEND</tt> since
|
|
every call is a first time.<br><br></p></li>
|
|
|
|
<li><tt>MXML_DESCEND</tt> means to keep descending until
|
|
you hit the bottom of the tree. The previous node from
|
|
"group" would be the "val3" node and the next node would
|
|
be the first node element under "group".
|
|
|
|
<p>If you were to walk from the root node "?xml" to the end
|
|
of the tree with <tt>mxmlWalkNext()</tt>, the order would
|
|
be:</p>
|
|
|
|
<p><tt>?xml data node val1 node val2 node val3 group node
|
|
val4 node val5 node val6 node val7 node val8</tt></p>
|
|
|
|
<p>If you started at "val8" and walked using
|
|
<tt>mxmlWalkPrev()</tt>, the order would be reversed,
|
|
ending at "?xml".</p></li>
|
|
|
|
</ul>
|
|
|
|
<h2>Finding Specific Nodes</h2>
|
|
|
|
<p>You can find specific nodes in the tree using the <a
|
|
href='#mxmlFindValue'><tt>mxmlFindPath</tt></a>, for example:
|
|
|
|
<pre>
|
|
mxml_node_t *value;
|
|
|
|
value = mxmlFindPath(tree, "path/to/*/foo/bar");
|
|
</pre>
|
|
|
|
<p>The second argument is a "path" to the parent node. Each component of the
|
|
path is separated by a slash (/) and represents a named element in the document
|
|
tree or a wildcard (*) path representing 0 or more intervening nodes.</p>
|
|
|
|
</body>
|
|
</html>
|