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| author | arseny.kapoulkine <arseny.kapoulkine@99668b35-9821-0410-8761-19e4c4f06640> | 2010-07-11 16:27:23 +0000 |
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| committer | arseny.kapoulkine <arseny.kapoulkine@99668b35-9821-0410-8761-19e4c4f06640> | 2010-07-11 16:27:23 +0000 |
| commit | f9a2dec792d9a52e1b9004793cfca9b0a463049a (patch) | |
| tree | 4a5cf5ded896dd3ea485e01d0c41e2b94b973385 /docs/manual/xpath.html | |
| parent | 468399c2eb1a9828310b11caf0c720785fd9c604 (diff) | |
docs: Added generated HTML documentation
git-svn-id: http://pugixml.googlecode.com/svn/trunk@596 99668b35-9821-0410-8761-19e4c4f06640
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diff --git a/docs/manual/xpath.html b/docs/manual/xpath.html new file mode 100644 index 0000000..731a969 --- /dev/null +++ b/docs/manual/xpath.html @@ -0,0 +1,494 @@ +<html> +<head> +<meta http-equiv="Content-Type" content="text/html; charset=US-ASCII"> +<title>XPath</title> +<link rel="stylesheet" href="../pugixml.css" type="text/css"> +<meta name="generator" content="DocBook XSL Stylesheets V1.75.2"> +<link rel="home" href="../manual.html" title="pugixml 0.9"> +<link rel="up" href="../manual.html" title="pugixml 0.9"> +<link rel="prev" href="saving.html" title="Saving document"> +<link rel="next" href="changes.html" title="Changelog"> +</head> +<body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"> +<table width="100%"><tr> +<td>pugixml 0.9 manual | + <a href="../manual.html">Overview</a> | + <a href="install.html">Installation</a> | + Document: + <a href="dom.html">Object model</a> · <a href="loading.html">Loading</a> · <a href="access.html">Accessing</a> · <a href="modify.html">Modifying</a> · <a href="saving.html">Saving</a> | + <b>XPath</b> | + <a href="apiref.html">API Reference</a> | + <a href="toc.html">Table of Contents</a> +</td> +<td width="*" align="right"><div class="spirit-nav"> +<a accesskey="p" href="saving.html"><img src="../images/prev.png" alt="Prev"></a><a accesskey="u" href="../manual.html"><img src="../images/up.png" alt="Up"></a><a accesskey="h" href="../manual.html"><img src="../images/home.png" alt="Home"></a><a accesskey="n" href="changes.html"><img src="../images/next.png" alt="Next"></a> +</div></td> +</tr></table> +<hr> +<div class="section"> +<div class="titlepage"><div><div><h2 class="title" style="clear: both"> +<a name="manual.xpath"></a><a class="link" href="xpath.html" title="XPath"> XPath</a> +</h2></div></div></div> +<div class="toc"><dl> +<dt><span class="section"><a href="xpath.html#manual.xpath.types"> XPath types</a></span></dt> +<dt><span class="section"><a href="xpath.html#manual.xpath.select"> Selecting nodes via XPath expression</a></span></dt> +<dt><span class="section"><a href="xpath.html#manual.xpath.query"> Using query objects</a></span></dt> +<dt><span class="section"><a href="xpath.html#manual.xpath.errors"> Error handling</a></span></dt> +<dt><span class="section"><a href="xpath.html#manual.xpath.w3c"> Conformance to W3C specification</a></span></dt> +</dl></div> +<p> + If the task at hand is to select a subset of document nodes that match some + criteria, it is possible to code a function using the existing traversal functionality + for any practical criteria. However, often either a data-driven approach is + desirable, in case the criteria are not predefined and come from a file, or + it is inconvenient to use traversal interfaces and a higher-level DSL is required. + There is a standard language for XML processing, XPath, that can be useful + for these cases. pugixml implements an almost complete subset of XPath 1.0. + Because of differences in document object model and some performance implications, + there are minor violations of the official specifications, which can be found + in <a class="xref" href="xpath.html#manual.xpath.w3c" title="Conformance to W3C specification"> Conformance to W3C specification</a>. The rest of this section describes the interface for XPath + functionality. Please note that if you wish to learn to use XPath language, + you have to look for other tutorials or manuals; for example, you can read + <a href="http://www.w3schools.com/xpath/" target="_top">W3Schools XPath tutorial</a>, + <a href="http://www.tizag.com/xmlTutorial/xpathtutorial.php" target="_top">XPath tutorial + at tizag.com</a>, and <a href="http://www.w3.org/TR/xpath/" target="_top">the XPath + 1.0 specification</a>. + </p> +<div class="note"><table border="0" summary="Note"> +<tr> +<td rowspan="2" align="center" valign="top" width="25"><img alt="[Note]" src="../images/note.png"></td> +<th align="left">Note</th> +</tr> +<tr><td align="left" valign="top"><p> + As of version 0.9, you need both STL and exception support to use XPath; + XPath is disabled if either <code class="computeroutput"><span class="identifier">PUGIXML_NO_STL</span></code> + or <code class="computeroutput"><span class="identifier">PUGIXML_NO_EXCEPTIONS</span></code> + is defined. + </p></td></tr> +</table></div> +<div class="section"> +<div class="titlepage"><div><div><h3 class="title"> +<a name="manual.xpath.types"></a><a class="link" href="xpath.html#manual.xpath.types" title="XPath types"> XPath types</a> +</h3></div></div></div> +<a name="xpath_value_type"></a><a name="xpath_type_number"></a><a name="xpath_type_string"></a><a name="xpath_type_boolean"></a><a name="xpath_type_node_set"></a><a name="xpath_type_none"></a><p> + Each XPath expression can have one of the following types: boolean, number, + string or node set. Boolean type corresponds to <code class="computeroutput"><span class="keyword">bool</span></code> + type, number type corresponds to <code class="computeroutput"><span class="keyword">double</span></code> + type, string type corresponds to either <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span></code> + or <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">wstring</span></code>, depending on whether <a class="link" href="dom.html#manual.dom.unicode" title="Unicode interface">wide + character interface is enabled</a>, and node set corresponds to <code class="computeroutput"><span class="identifier">xpath_node_set</span></code> type. There is an enumeration, + <code class="computeroutput"><span class="identifier">xpath_value_type</span></code>, which can + take the values <code class="computeroutput"><span class="identifier">xpath_type_boolean</span></code>, + <code class="computeroutput"><span class="identifier">xpath_type_number</span></code>, <code class="computeroutput"><span class="identifier">xpath_type_string</span></code> or <code class="computeroutput"><span class="identifier">xpath_type_node_set</span></code>, + accordingly. + </p> +<a name="xpath_node"></a><a name="xpath_node::node"></a><a name="xpath_node::attribute"></a><a name="xpath_node::parent"></a><p> + Because an XPath node can be either a node or an attribute, there is a special + type, <code class="computeroutput"><span class="identifier">xpath_node</span></code>, which is + a discriminated union of these types. A value of this type contains two node + handles, one of <code class="computeroutput"><span class="identifier">xml_node</span></code> + type, and another one of <code class="computeroutput"><span class="identifier">xml_attribute</span></code> + type; at most one of them can be non-null. The accessors to get these handles + are available: + </p> +<pre class="programlisting"><span class="identifier">xml_node</span> <span class="identifier">xpath_node</span><span class="special">::</span><span class="identifier">node</span><span class="special">()</span> <span class="keyword">const</span><span class="special">;</span> +<span class="identifier">xml_attribute</span> <span class="identifier">xpath_node</span><span class="special">::</span><span class="identifier">attribute</span><span class="special">()</span> <span class="keyword">const</span><span class="special">;</span> +</pre> +<p> + XPath nodes can be null, in which case both accessors return null handles. + </p> +<p> + Note that as per XPath specification, each XPath node has a parent, which + can be retrieved via this function: + </p> +<pre class="programlisting"><span class="identifier">xml_node</span> <span class="identifier">xpath_node</span><span class="special">::</span><span class="identifier">parent</span><span class="special">()</span> <span class="keyword">const</span><span class="special">;</span> +</pre> +<p> + <code class="computeroutput"><span class="identifier">parent</span></code> function returns the + node's parent if the XPath node corresponds to <code class="computeroutput"><span class="identifier">xml_node</span></code> + handle (equivalent to <code class="computeroutput"><span class="identifier">node</span><span class="special">().</span><span class="identifier">parent</span><span class="special">()</span></code>), or the node to which the attribute belongs + to, if the XPath node corresponds to <code class="computeroutput"><span class="identifier">xml_attribute</span></code> + handle. For null nodes, <code class="computeroutput"><span class="identifier">parent</span></code> + returns null handle. + </p> +<a name="xpath_node::unspecified_bool_type"></a><a name="xpath_node::comparison"></a><p> + Like node and attribute handles, XPath node handles can be implicitly cast + to boolean-like object to check if it is a null node, and also can be compared + for equality with each other. + </p> +<a name="xpath_node::ctor"></a><p> + You can also create XPath nodes with one of tree constructors: the default + constructor, the constructor that takes node argument, and the constructor + that takes attribute and node arguments (in which case the attribute must + belong to the attribute list of the node). However, usually you don't need + to create your own XPath node objects, since they are returned to you via + selection functions. + </p> +<a name="xpath_node_set"></a><p> + XPath expressions operate not on single nodes, but instead on node sets. + A node set is a collection of nodes, which can be optionally ordered in either + a forward document order or a reverse one. Document order is defined in XPath + specification; an XPath node is before another node in document order if + it appears before it in XML representation of the corresponding document. + </p> +<a name="xpath_node_set::const_iterator"></a><a name="xpath_node_set::begin"></a><a name="xpath_node_set::end"></a><p> + Node sets are represented by <code class="computeroutput"><span class="identifier">xpath_node_set</span></code> + object, which has an interface that resembles one of sequential random-access + containers. It has an iterator type along with usual begin/past-the-end iterator + accessors: + </p> +<pre class="programlisting"><span class="keyword">typedef</span> <span class="keyword">const</span> <span class="identifier">xpath_node</span><span class="special">*</span> <span class="identifier">xpath_node_set</span><span class="special">::</span><span class="identifier">const_iterator</span><span class="special">;</span> +<span class="identifier">const_iterator</span> <span class="identifier">xpath_node_set</span><span class="special">::</span><span class="identifier">begin</span><span class="special">()</span> <span class="keyword">const</span><span class="special">;</span> +<span class="identifier">const_iterator</span> <span class="identifier">xpath_node_set</span><span class="special">::</span><span class="identifier">end</span><span class="special">()</span> <span class="keyword">const</span><span class="special">;</span> +</pre> +<a name="xpath_node_set::index"></a><a name="xpath_node_set::size"></a><a name="xpath_node_set::empty"></a><p> + And it also can be iterated via indices, just like <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">vector</span></code>: + </p> +<pre class="programlisting"><span class="keyword">const</span> <span class="identifier">xpath_node</span><span class="special">&</span> <span class="identifier">xpath_node_set</span><span class="special">::</span><span class="keyword">operator</span><span class="special">[](</span><span class="identifier">size_t</span> <span class="identifier">index</span><span class="special">)</span> <span class="keyword">const</span><span class="special">;</span> +<span class="identifier">size_t</span> <span class="identifier">xpath_node_set</span><span class="special">::</span><span class="identifier">size</span><span class="special">()</span> <span class="keyword">const</span><span class="special">;</span> +<span class="keyword">bool</span> <span class="identifier">xpath_node_set</span><span class="special">::</span><span class="identifier">empty</span><span class="special">()</span> <span class="keyword">const</span><span class="special">;</span> +</pre> +<p> + All of the above operations have the same semantics as that of <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">vector</span></code>: + the iterators are random-access, all of the above operations are constant + time, and accessing the element at index that is greater or equal than the + set size results in undefined behavior. You can use both iterator-based and + index-based access for iteration, however the iterator-based can be faster. + </p> +<a name="xpath_node_set::type"></a><a name="xpath_node_set::type_unsorted"></a><a name="xpath_node_set::type_sorted"></a><a name="xpath_node_set::type_sorted_reverse"></a><a name="xpath_node_set::sort"></a><p> + The order of iteration depends on the order of nodes inside the set; the + order can be queried via the following function: + </p> +<pre class="programlisting"><span class="keyword">enum</span> <span class="identifier">xpath_node_set</span><span class="special">::</span><span class="identifier">type_t</span> <span class="special">{</span><span class="identifier">type_unsorted</span><span class="special">,</span> <span class="identifier">type_sorted</span><span class="special">,</span> <span class="identifier">type_sorted_reverse</span><span class="special">};</span> +<span class="identifier">type_t</span> <span class="identifier">xpath_node_set</span><span class="special">::</span><span class="identifier">type</span><span class="special">()</span> <span class="keyword">const</span><span class="special">;</span> +</pre> +<p> + <code class="computeroutput"><span class="identifier">type</span></code> function returns the + current order of nodes; <code class="computeroutput"><span class="identifier">type_sorted</span></code> + means that the nodes are in forward document order, <code class="computeroutput"><span class="identifier">type_sorted_reverse</span></code> + means that the nodes are in reverse document order, and <code class="computeroutput"><span class="identifier">type_unsorted</span></code> + means that neither order is guaranteed (nodes can accidentally be in a sorted + order even if <code class="computeroutput"><span class="identifier">type</span><span class="special">()</span></code> + returns <code class="computeroutput"><span class="identifier">type_unsorted</span></code>). If + you require a specific order of iteration, you can change it via <code class="computeroutput"><span class="identifier">sort</span></code> function: + </p> +<pre class="programlisting"><span class="keyword">void</span> <span class="identifier">xpath_node_set</span><span class="special">::</span><span class="identifier">sort</span><span class="special">(</span><span class="keyword">bool</span> <span class="identifier">reverse</span> <span class="special">=</span> <span class="keyword">false</span><span class="special">);</span> +</pre> +<p> + Calling <code class="computeroutput"><span class="identifier">sort</span></code> sorts the nodes + in either forward or reverse document order, depending on the argument; after + this call <code class="computeroutput"><span class="identifier">type</span><span class="special">()</span></code> + will return <code class="computeroutput"><span class="identifier">type_sorted</span></code> or + <code class="computeroutput"><span class="identifier">type_sorted_reverse</span></code>. + </p> +<a name="xpath_node_set::first"></a><p> + Often the actual iteration is not needed; instead, only the first element + in document order is required. For this, a special accessor is provided: + </p> +<pre class="programlisting"><span class="identifier">xpath_node</span> <span class="identifier">xpath_node_set</span><span class="special">::</span><span class="identifier">first</span><span class="special">()</span> <span class="keyword">const</span><span class="special">;</span> +</pre> +<p> + This function returns the first node in forward document order from the set, + or null node if the set is empty. Note that while the result of the node + does not depend on the order of nodes in the set (i.e. on the result of + <code class="computeroutput"><span class="identifier">type</span><span class="special">()</span></code>), + the complexity does - if the set is sorted, the complexity is constant, otherwise + it is linear in the number of elements or worse. + </p> +</div> +<div class="section"> +<div class="titlepage"><div><div><h3 class="title"> +<a name="manual.xpath.select"></a><a class="link" href="xpath.html#manual.xpath.select" title="Selecting nodes via XPath expression"> Selecting nodes via XPath expression</a> +</h3></div></div></div> +<a name="xml_node::select_single_node"></a><a name="xml_node::select_nodes"></a><p> + If you want to select nodes that match some XPath expression, you can do + it with the following functions: + </p> +<pre class="programlisting"><span class="identifier">xpath_node</span> <span class="identifier">xml_node</span><span class="special">::</span><span class="identifier">select_single_node</span><span class="special">(</span><span class="keyword">const</span> <span class="identifier">char_t</span><span class="special">*</span> <span class="identifier">query</span><span class="special">)</span> <span class="keyword">const</span><span class="special">;</span> +<span class="identifier">xpath_node_set</span> <span class="identifier">xml_node</span><span class="special">::</span><span class="identifier">select_nodes</span><span class="special">(</span><span class="keyword">const</span> <span class="identifier">char_t</span><span class="special">*</span> <span class="identifier">query</span><span class="special">)</span> <span class="keyword">const</span><span class="special">;</span> +</pre> +<p> + <code class="computeroutput"><span class="identifier">select_nodes</span></code> function compiles + the expression and then executes it with the node as a context node, and + returns the resulting node set. <code class="computeroutput"><span class="identifier">select_single_node</span></code> + returns only the first node in document order from the result, and is equivalent + to calling <code class="computeroutput"><span class="identifier">select_nodes</span><span class="special">(</span><span class="identifier">query</span><span class="special">).</span><span class="identifier">first</span><span class="special">()</span></code>. + If the XPath expression does not match anything, or the node handle is null, + <code class="computeroutput"><span class="identifier">select_nodes</span></code> returns an empty + set, and <code class="computeroutput"><span class="identifier">select_single_node</span></code> + returns null XPath node. + </p> +<p> + Both functions throw <code class="computeroutput"><span class="identifier">xpath_exception</span></code> + if the query can not be compiled or if it returns a value with type other + than node set; see <a class="xref" href="xpath.html#manual.xpath.errors" title="Error handling"> Error handling</a> for details. + </p> +<a name="xml_node::select_single_node_precomp"></a><a name="xml_node::select_nodes_precomp"></a><p> + While compiling expressions is fast, the compilation time can introduce a + significant overhead if the same expression is used many times on small subtrees. + If you're doing many similar queries, consider compiling them into query + objects (see <a class="xref" href="xpath.html#manual.xpath.query" title="Using query objects"> Using query objects</a> for further reference). Once you get a compiled + query object, you can pass it to select functions instead of an expression + string: + </p> +<pre class="programlisting"><span class="identifier">xpath_node</span> <span class="identifier">xml_node</span><span class="special">::</span><span class="identifier">select_single_node</span><span class="special">(</span><span class="keyword">const</span> <span class="identifier">xpath_query</span><span class="special">&</span> <span class="identifier">query</span><span class="special">)</span> <span class="keyword">const</span><span class="special">;</span> +<span class="identifier">xpath_node_set</span> <span class="identifier">xml_node</span><span class="special">::</span><span class="identifier">select_nodes</span><span class="special">(</span><span class="keyword">const</span> <span class="identifier">xpath_query</span><span class="special">&</span> <span class="identifier">query</span><span class="special">)</span> <span class="keyword">const</span><span class="special">;</span> +</pre> +<p> + Both functions throw <code class="computeroutput"><span class="identifier">xpath_exception</span></code> + if the query returns a value with type other than node set. + </p> +<p> + This is an example of selecting nodes using XPath expressions (<a href="../samples/xpath_select.cpp" target="_top">samples/xpath_select.cpp</a>): + </p> +<p> + +</p> +<pre class="programlisting"><span class="identifier">pugi</span><span class="special">::</span><span class="identifier">xpath_node_set</span> <span class="identifier">tools</span> <span class="special">=</span> <span class="identifier">doc</span><span class="special">.</span><span class="identifier">select_nodes</span><span class="special">(</span><span class="string">"/Profile/Tools/Tool[@AllowRemote='true' and @DeriveCaptionFrom='lastparam']"</span><span class="special">);</span> + +<span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span> <span class="special"><<</span> <span class="string">"Tools:"</span><span class="special">;</span> + +<span class="keyword">for</span> <span class="special">(</span><span class="identifier">pugi</span><span class="special">::</span><span class="identifier">xpath_node_set</span><span class="special">::</span><span class="identifier">const_iterator</span> <span class="identifier">it</span> <span class="special">=</span> <span class="identifier">tools</span><span class="special">.</span><span class="identifier">begin</span><span class="special">();</span> <span class="identifier">it</span> <span class="special">!=</span> <span class="identifier">tools</span><span class="special">.</span><span class="identifier">end</span><span class="special">();</span> <span class="special">++</span><span class="identifier">it</span><span class="special">)</span> +<span class="special">{</span> + <span class="identifier">pugi</span><span class="special">::</span><span class="identifier">xpath_node</span> <span class="identifier">node</span> <span class="special">=</span> <span class="special">*</span><span class="identifier">it</span><span class="special">;</span> + <span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span> <span class="special"><<</span> <span class="string">" "</span> <span class="special"><<</span> <span class="identifier">node</span><span class="special">.</span><span class="identifier">node</span><span class="special">().</span><span class="identifier">attribute</span><span class="special">(</span><span class="string">"Filename"</span><span class="special">).</span><span class="identifier">value</span><span class="special">();</span> +<span class="special">}</span> + +<span class="identifier">pugi</span><span class="special">::</span><span class="identifier">xpath_node</span> <span class="identifier">build_tool</span> <span class="special">=</span> <span class="identifier">doc</span><span class="special">.</span><span class="identifier">select_single_node</span><span class="special">(</span><span class="string">"//Tool[contains(Description, 'build system')]"</span><span class="special">);</span> + +<span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span> <span class="special"><<</span> <span class="string">"\nBuild tool: "</span> <span class="special"><<</span> <span class="identifier">build_tool</span><span class="special">.</span><span class="identifier">node</span><span class="special">().</span><span class="identifier">attribute</span><span class="special">(</span><span class="string">"Filename"</span><span class="special">).</span><span class="identifier">value</span><span class="special">()</span> <span class="special"><<</span> <span class="string">"\n"</span><span class="special">;</span> +</pre> +<p> + </p> +</div> +<div class="section"> +<div class="titlepage"><div><div><h3 class="title"> +<a name="manual.xpath.query"></a><a class="link" href="xpath.html#manual.xpath.query" title="Using query objects"> Using query objects</a> +</h3></div></div></div> +<a name="xpath_query"></a><p> + When you call <code class="computeroutput"><span class="identifier">select_nodes</span></code> + with an expression string as an argument, a query object is created behind + the scene. A query object represents a compiled XPath expression. Query objects + can be needed in the following circumstances: + </p> +<div class="itemizedlist"><ul class="itemizedlist" type="disc"> +<li class="listitem"> + You can precompile expressions to query objects to save compilation time + if it becomes an issue; + </li> +<li class="listitem"> + You can use query objects to evaluate XPath expressions which result + in booleans, numbers or strings; + </li> +<li class="listitem"> + You can get the type of expression value via query object. + </li> +</ul></div> +<p> + Query objects correspond to <code class="computeroutput"><span class="identifier">xpath_query</span></code> + type. They are immutable and non-copyable: they are bound to the expression + at creation time and can not be cloned. If you want to put query objects + in a container, allocate them on heap via <code class="computeroutput"><span class="keyword">new</span></code> + operator and store pointers to <code class="computeroutput"><span class="identifier">xpath_query</span></code> + in the container. + </p> +<a name="xpath_query::ctor"></a><p> + You can create a query object with the constructor that takes XPath expression + as an argument: + </p> +<pre class="programlisting"><span class="keyword">explicit</span> <span class="identifier">xpath_query</span><span class="special">::</span><span class="identifier">xpath_query</span><span class="special">(</span><span class="keyword">const</span> <span class="identifier">char_t</span><span class="special">*</span> <span class="identifier">query</span><span class="special">);</span> +</pre> +<a name="xpath_query::return_type"></a><p> + The expression is compiled and the compiled representation is stored in the + new query object. If compilation fails, <code class="computeroutput"><span class="identifier">xpath_exception</span></code> + is thrown (see <a class="xref" href="xpath.html#manual.xpath.errors" title="Error handling"> Error handling</a> for details). After the query is created, + you can query the type of the evaluation result using the following function: + </p> +<pre class="programlisting"><span class="identifier">xpath_value_type</span> <span class="identifier">xpath_query</span><span class="special">::</span><span class="identifier">return_type</span><span class="special">()</span> <span class="keyword">const</span><span class="special">;</span> +</pre> +<a name="xpath_query::evaluate_boolean"></a><a name="xpath_query::evaluate_number"></a><a name="xpath_query::evaluate_string"></a><a name="xpath_query::evaluate_node_set"></a><p> + You can evaluate the query using one of the following functions: + </p> +<pre class="programlisting"><span class="keyword">bool</span> <span class="identifier">xpath_query</span><span class="special">::</span><span class="identifier">evaluate_boolean</span><span class="special">(</span><span class="keyword">const</span> <span class="identifier">xml_node</span><span class="special">&</span> <span class="identifier">n</span><span class="special">)</span> <span class="keyword">const</span><span class="special">;</span> +<span class="keyword">double</span> <span class="identifier">xpath_query</span><span class="special">::</span><span class="identifier">evaluate_number</span><span class="special">(</span><span class="keyword">const</span> <span class="identifier">xml_node</span><span class="special">&</span> <span class="identifier">n</span><span class="special">)</span> <span class="keyword">const</span><span class="special">;</span> +<span class="identifier">string_t</span> <span class="identifier">xpath_query</span><span class="special">::</span><span class="identifier">evaluate_string</span><span class="special">(</span><span class="keyword">const</span> <span class="identifier">xml_node</span><span class="special">&</span> <span class="identifier">n</span><span class="special">)</span> <span class="keyword">const</span><span class="special">;</span> +<span class="identifier">xpath_node_set</span> <span class="identifier">xpath_query</span><span class="special">::</span><span class="identifier">evaluate_node_set</span><span class="special">(</span><span class="keyword">const</span> <span class="identifier">xml_node</span><span class="special">&</span> <span class="identifier">n</span><span class="special">)</span> <span class="keyword">const</span><span class="special">;</span> +</pre> +<p> + All functions take the context node as an argument, compute the expression + and return the result, converted to the requested type. By XPath specification, + value of any type can be converted to boolean, number or string value, but + no type other than node set can be converted to node set. Because of this, + <code class="computeroutput"><span class="identifier">evaluate_boolean</span></code>, <code class="computeroutput"><span class="identifier">evaluate_number</span></code> and <code class="computeroutput"><span class="identifier">evaluate_string</span></code> + always return a result, but <code class="computeroutput"><span class="identifier">evaluate_node_set</span></code> + throws an <code class="computeroutput"><span class="identifier">xpath_exception</span></code> + if the return type is not node set. + </p> +<div class="note"><table border="0" summary="Note"> +<tr> +<td rowspan="2" align="center" valign="top" width="25"><img alt="[Note]" src="../images/note.png"></td> +<th align="left">Note</th> +</tr> +<tr><td align="left" valign="top"><p> + Calling <code class="computeroutput"><span class="identifier">node</span><span class="special">.</span><span class="identifier">select_nodes</span><span class="special">(</span><span class="string">"query"</span><span class="special">)</span></code> + is equivalent to calling <code class="computeroutput"><span class="identifier">xpath_query</span><span class="special">(</span><span class="string">"query"</span><span class="special">).</span><span class="identifier">evaluate_node_set</span><span class="special">(</span><span class="identifier">node</span><span class="special">)</span></code>. + </p></td></tr> +</table></div> +<p> + This is an example of using query objects (<a href="../samples/xpath_query.cpp" target="_top">samples/xpath_query.cpp</a>): + </p> +<p> + +</p> +<pre class="programlisting"><span class="comment">// Select nodes via compiled query +</span><span class="identifier">pugi</span><span class="special">::</span><span class="identifier">xpath_query</span> <span class="identifier">query_remote_tools</span><span class="special">(</span><span class="string">"/Profile/Tools/Tool[@AllowRemote='true']"</span><span class="special">);</span> + +<span class="identifier">pugi</span><span class="special">::</span><span class="identifier">xpath_node_set</span> <span class="identifier">tools</span> <span class="special">=</span> <span class="identifier">query_remote_tools</span><span class="special">.</span><span class="identifier">evaluate_node_set</span><span class="special">(</span><span class="identifier">doc</span><span class="special">);</span> +<span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span> <span class="special"><<</span> <span class="string">"Remote tool: "</span><span class="special">;</span> +<span class="identifier">tools</span><span class="special">[</span><span class="number">2</span><span class="special">].</span><span class="identifier">node</span><span class="special">().</span><span class="identifier">print</span><span class="special">(</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span><span class="special">);</span> + +<span class="comment">// Evaluate numbers via compiled query +</span><span class="identifier">pugi</span><span class="special">::</span><span class="identifier">xpath_query</span> <span class="identifier">query_timeouts</span><span class="special">(</span><span class="string">"sum(//Tool/@Timeout)"</span><span class="special">);</span> +<span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span> <span class="special"><<</span> <span class="identifier">query_timeouts</span><span class="special">.</span><span class="identifier">evaluate_number</span><span class="special">(</span><span class="identifier">doc</span><span class="special">)</span> <span class="special"><<</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">endl</span><span class="special">;</span> + +<span class="comment">// Evaluate strings via compiled query for different context nodes +</span><span class="identifier">pugi</span><span class="special">::</span><span class="identifier">xpath_query</span> <span class="identifier">query_name_valid</span><span class="special">(</span><span class="string">"string-length(substring-before(@Filename, '_')) > 0 and @OutputFileMasks"</span><span class="special">);</span> +<span class="identifier">pugi</span><span class="special">::</span><span class="identifier">xpath_query</span> <span class="identifier">query_name</span><span class="special">(</span><span class="string">"concat(substring-before(@Filename, '_'), ' produces ', @OutputFileMasks)"</span><span class="special">);</span> + +<span class="keyword">for</span> <span class="special">(</span><span class="identifier">pugi</span><span class="special">::</span><span class="identifier">xml_node</span> <span class="identifier">tool</span> <span class="special">=</span> <span class="identifier">doc</span><span class="special">.</span><span class="identifier">first_element_by_path</span><span class="special">(</span><span class="string">"Profile/Tools/Tool"</span><span class="special">);</span> <span class="identifier">tool</span><span class="special">;</span> <span class="identifier">tool</span> <span class="special">=</span> <span class="identifier">tool</span><span class="special">.</span><span class="identifier">next_sibling</span><span class="special">())</span> +<span class="special">{</span> + <span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span> <span class="identifier">s</span> <span class="special">=</span> <span class="identifier">query_name</span><span class="special">.</span><span class="identifier">evaluate_string</span><span class="special">(</span><span class="identifier">tool</span><span class="special">);</span> + + <span class="keyword">if</span> <span class="special">(</span><span class="identifier">query_name_valid</span><span class="special">.</span><span class="identifier">evaluate_boolean</span><span class="special">(</span><span class="identifier">tool</span><span class="special">))</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span> <span class="special"><<</span> <span class="identifier">s</span> <span class="special"><<</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">endl</span><span class="special">;</span> +<span class="special">}</span> +</pre> +<p> + </p> +</div> +<div class="section"> +<div class="titlepage"><div><div><h3 class="title"> +<a name="manual.xpath.errors"></a><a class="link" href="xpath.html#manual.xpath.errors" title="Error handling"> Error handling</a> +</h3></div></div></div> +<a name="xpath_exception"></a><a name="xpath_exception::what"></a><p> + As of version 0.9, all XPath errors result in thrown exceptions. The errors + can arise during expression compilation or node set evaluation. In both cases, + an <code class="computeroutput"><span class="identifier">xpath_exception</span></code> object + is thrown. This is an exception object that implements <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">exception</span></code> + interface, and thus has a single function <code class="computeroutput"><span class="identifier">what</span><span class="special">()</span></code>: + </p> +<pre class="programlisting"><span class="keyword">virtual</span> <span class="keyword">const</span> <span class="keyword">char</span><span class="special">*</span> <span class="identifier">xpath_exception</span><span class="special">::</span><span class="identifier">what</span><span class="special">()</span> <span class="keyword">const</span> <span class="keyword">throw</span><span class="special">();</span> +</pre> +<p> + This function returns the error message. Currently it is impossible to get + the exact place where query compilation failed. This functionality, along + with optional error handling without exceptions, will be available in version + 1.0. + </p> +<p> + This is an example of XPath error handling (<a href="../samples/xpath_error.cpp" target="_top">samples/xpath_error.cpp</a>): + </p> +<p> + +</p> +<pre class="programlisting"><span class="comment">// Exception is thrown for incorrect query syntax +</span><span class="keyword">try</span> +<span class="special">{</span> + <span class="identifier">doc</span><span class="special">.</span><span class="identifier">select_nodes</span><span class="special">(</span><span class="string">"//nodes[#true()]"</span><span class="special">);</span> +<span class="special">}</span> +<span class="keyword">catch</span> <span class="special">(</span><span class="keyword">const</span> <span class="identifier">pugi</span><span class="special">::</span><span class="identifier">xpath_exception</span><span class="special">&</span> <span class="identifier">e</span><span class="special">)</span> +<span class="special">{</span> + <span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span> <span class="special"><<</span> <span class="string">"Select failed: "</span> <span class="special"><<</span> <span class="identifier">e</span><span class="special">.</span><span class="identifier">what</span><span class="special">()</span> <span class="special"><<</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">endl</span><span class="special">;</span> +<span class="special">}</span> + +<span class="comment">// Exception is thrown for incorrect query semantics +</span><span class="keyword">try</span> +<span class="special">{</span> + <span class="identifier">doc</span><span class="special">.</span><span class="identifier">select_nodes</span><span class="special">(</span><span class="string">"(123)/next"</span><span class="special">);</span> +<span class="special">}</span> +<span class="keyword">catch</span> <span class="special">(</span><span class="keyword">const</span> <span class="identifier">pugi</span><span class="special">::</span><span class="identifier">xpath_exception</span><span class="special">&</span> <span class="identifier">e</span><span class="special">)</span> +<span class="special">{</span> + <span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span> <span class="special"><<</span> <span class="string">"Select failed: "</span> <span class="special"><<</span> <span class="identifier">e</span><span class="special">.</span><span class="identifier">what</span><span class="special">()</span> <span class="special"><<</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">endl</span><span class="special">;</span> +<span class="special">}</span> + +<span class="comment">// Exception is thrown for query with incorrect return type +</span><span class="keyword">try</span> +<span class="special">{</span> + <span class="identifier">doc</span><span class="special">.</span><span class="identifier">select_nodes</span><span class="special">(</span><span class="string">"123"</span><span class="special">);</span> +<span class="special">}</span> +<span class="keyword">catch</span> <span class="special">(</span><span class="keyword">const</span> <span class="identifier">pugi</span><span class="special">::</span><span class="identifier">xpath_exception</span><span class="special">&</span> <span class="identifier">e</span><span class="special">)</span> +<span class="special">{</span> + <span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span> <span class="special"><<</span> <span class="string">"Select failed: "</span> <span class="special"><<</span> <span class="identifier">e</span><span class="special">.</span><span class="identifier">what</span><span class="special">()</span> <span class="special"><<</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">endl</span><span class="special">;</span> +<span class="special">}</span> +</pre> +<p> + </p> +</div> +<div class="section"> +<div class="titlepage"><div><div><h3 class="title"> +<a name="manual.xpath.w3c"></a><a class="link" href="xpath.html#manual.xpath.w3c" title="Conformance to W3C specification"> Conformance to W3C specification</a> +</h3></div></div></div> +<p> + Because of the differences in document object models, performance considerations + and implementation complexity, pugixml does not provide a fully conformant + XPath 1.0 implementation. This is the current list of incompatibilities: + </p> +<div class="itemizedlist"><ul class="itemizedlist" type="disc"> +<li class="listitem"> + Consecutive text nodes sharing the same parent are not merged, i.e. in + <code class="computeroutput"><span class="special"><</span><span class="identifier">node</span><span class="special">></span><span class="identifier">text1</span> + <span class="special"><![</span><span class="identifier">CDATA</span><span class="special">[</span><span class="identifier">data</span><span class="special">]]></span> <span class="identifier">text2</span><span class="special"></</span><span class="identifier">node</span><span class="special">></span></code> node should have one text node children, + but instead has three. + </li> +<li class="listitem"> + Since document can't have a document type declaration, <code class="computeroutput"><span class="identifier">id</span><span class="special">()</span></code> + function always returns an empty node set. + </li> +<li class="listitem"> + Namespace nodes are not supported (affects namespace:: axis). + </li> +<li class="listitem"> + Name tests are performed on QNames in XML document instead of expanded + names; for <code class="computeroutput"><span class="special"><</span><span class="identifier">foo</span> + <span class="identifier">xmlns</span><span class="special">:</span><span class="identifier">ns1</span><span class="special">=</span><span class="char">'uri'</span> <span class="identifier">xmlns</span><span class="special">:</span><span class="identifier">ns2</span><span class="special">=</span><span class="char">'uri'</span><span class="special">><</span><span class="identifier">ns1</span><span class="special">:</span><span class="identifier">child</span><span class="special">/><</span><span class="identifier">ns2</span><span class="special">:</span><span class="identifier">child</span><span class="special">/></</span><span class="identifier">foo</span><span class="special">></span></code>, + query <code class="computeroutput"><span class="identifier">foo</span><span class="special">/</span><span class="identifier">ns1</span><span class="special">:*</span></code> + will return only the first child, not both of them. Compliant XPath implementations + can return both nodes if the user provides appropriate namespace declarations. + </li> +<li class="listitem"> + String functions consider a character to be either a single <code class="computeroutput"><span class="keyword">char</span></code> value or a single <code class="computeroutput"><span class="keyword">wchar_t</span></code> + value, depending on the library configuration; this means that some string + functions are not fully Unicode-aware. This affects <code class="computeroutput"><span class="identifier">substring</span><span class="special">()</span></code>, <code class="computeroutput"><span class="identifier">string</span><span class="special">-</span><span class="identifier">length</span><span class="special">()</span></code> and <code class="computeroutput"><span class="identifier">translate</span><span class="special">()</span></code> functions. + </li> +<li class="listitem"> + Variable references are not supported. + </li> +</ul></div> +<p> + Some of these incompatibilities will be fixed in version 1.0. + </p> +</div> +</div> +<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr> +<td align="left"></td> +<td align="right"><div class="copyright-footer">Copyright © 2010 Arseny Kapoulkine<p> + Distributed under the MIT License + </p> +</div></td> +</tr></table> +<hr> +<table width="100%"><tr> +<td>pugixml 0.9 manual | + <a href="../manual.html">Overview</a> | + <a href="install.html">Installation</a> | + Document: + <a href="dom.html">Object model</a> · <a href="loading.html">Loading</a> · <a href="access.html">Accessing</a> · <a href="modify.html">Modifying</a> · <a href="saving.html">Saving</a> | + <b>XPath</b> | + <a href="apiref.html">API Reference</a> | + <a href="toc.html">Table of Contents</a> +</td> +<td width="*" align="right"><div class="spirit-nav"> +<a accesskey="p" href="saving.html"><img src="../images/prev.png" alt="Prev"></a><a accesskey="u" href="../manual.html"><img src="../images/up.png" alt="Up"></a><a accesskey="h" href="../manual.html"><img src="../images/home.png" alt="Home"></a><a accesskey="n" href="changes.html"><img src="../images/next.png" alt="Next"></a> +</div></td> +</tr></table> +</body> +</html> |