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authorArseny Kapoulkine <arseny.kapoulkine@gmail.com>2015-04-10 22:26:57 -0700
committerArseny Kapoulkine <arseny.kapoulkine@gmail.com>2015-04-10 22:26:57 -0700
commite90d2ac8ba44fbcf4d5702643f708f2c86bde42e (patch)
treea52fe8e4efee8176da169998c203c1a93f6a6ff1 /docs/manual/dom.html
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-<html>
-<head>
-<meta http-equiv="Content-Type" content="text/html; charset=US-ASCII">
-<title>Document object model</title>
-<link rel="stylesheet" href="../pugixml.css" type="text/css">
-<meta name="generator" content="DocBook XSL Stylesheets V1.78.1">
-<link rel="home" href="../manual.html" title="pugixml 1.5">
-<link rel="up" href="../manual.html" title="pugixml 1.5">
-<link rel="prev" href="install.html" title="Installation">
-<link rel="next" href="loading.html" title="Loading document">
-</head>
-<body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF">
-<table width="100%"><tr>
-<td>
-<a href="http://pugixml.org/">pugixml 1.5</a> manual |
- <a href="../manual.html">Overview</a> |
- <a href="install.html">Installation</a> |
- Document:
- <b>Object model</b> &middot; <a href="loading.html">Loading</a> &middot; <a href="access.html">Accessing</a> &middot; <a href="modify.html">Modifying</a> &middot; <a href="saving.html">Saving</a> |
- <a href="xpath.html">XPath</a> |
- <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="install.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="loading.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.dom"></a><a class="link" href="dom.html" title="Document object model"> Document object model</a>
-</h2></div></div></div>
-<div class="toc"><dl class="toc">
-<dt><span class="section"><a href="dom.html#manual.dom.tree"> Tree structure</a></span></dt>
-<dt><span class="section"><a href="dom.html#manual.dom.cpp"> C++ interface</a></span></dt>
-<dt><span class="section"><a href="dom.html#manual.dom.unicode"> Unicode interface</a></span></dt>
-<dt><span class="section"><a href="dom.html#manual.dom.thread"> Thread-safety guarantees</a></span></dt>
-<dt><span class="section"><a href="dom.html#manual.dom.exception"> Exception guarantees</a></span></dt>
-<dt><span class="section"><a href="dom.html#manual.dom.memory"> Memory management</a></span></dt>
-<dd><dl>
-<dt><span class="section"><a href="dom.html#manual.dom.memory.custom"> Custom memory allocation/deallocation
- functions</a></span></dt>
-<dt><span class="section"><a href="dom.html#manual.dom.memory.tuning"> Memory consumption tuning</a></span></dt>
-<dt><span class="section"><a href="dom.html#manual.dom.memory.internals"> Document memory management
- internals</a></span></dt>
-</dl></dd>
-</dl></div>
-<p>
- pugixml stores XML data in DOM-like way: the entire XML document (both document
- structure and element data) is stored in memory as a tree. The tree can be
- loaded from a character stream (file, string, C++ I/O stream), then traversed
- with the special API or XPath expressions. The whole tree is mutable: both
- node structure and node/attribute data can be changed at any time. Finally,
- the result of document transformations can be saved to a character stream (file,
- C++ I/O stream or custom transport).
- </p>
-<div class="section">
-<div class="titlepage"><div><div><h3 class="title">
-<a name="manual.dom.tree"></a><a class="link" href="dom.html#manual.dom.tree" title="Tree structure"> Tree structure</a>
-</h3></div></div></div>
-<p>
- The XML document is represented with a tree data structure. The root of the
- tree is the document itself, which corresponds to C++ type <a class="link" href="dom.html#xml_document">xml_document</a>.
- Document has one or more child nodes, which correspond to C++ type <a class="link" href="dom.html#xml_node">xml_node</a>. Nodes have different types; depending
- on a type, a node can have a collection of child nodes, a collection of attributes,
- which correspond to C++ type <a class="link" href="dom.html#xml_attribute">xml_attribute</a>,
- and some additional data (i.e. name).
- </p>
-<a name="xml_node_type"></a><p>
- The tree nodes can be of one of the following types (which together form
- the enumeration <code class="computeroutput"><span class="identifier">xml_node_type</span></code>):
- </p>
-<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
-<li class="listitem">
- Document node (<a name="node_document"></a><code class="literal">node_document</code>) - this
- is the root of the tree, which consists of several child nodes. This
- node corresponds to <a class="link" href="dom.html#xml_document">xml_document</a>
- class; note that <a class="link" href="dom.html#xml_document">xml_document</a> is
- a sub-class of <a class="link" href="dom.html#xml_node">xml_node</a>, so the entire
- node interface is also available. However, document node is special in
- several ways, which are covered below. There can be only one document
- node in the tree; document node does not have any XML representation.
- <br><br>
-
- </li>
-<li class="listitem">
- Element/tag node (<a name="node_element"></a><code class="literal">node_element</code>) - this
- is the most common type of node, which represents XML elements. Element
- nodes have a name, a collection of attributes and a collection of child
- nodes (both of which may be empty). The attribute is a simple name/value
- pair. The example XML representation of element nodes is as follows:
- </li>
-</ul></div>
-<pre class="programlisting"><span class="special">&lt;</span><span class="identifier">node</span> <span class="identifier">attr</span><span class="special">=</span><span class="string">"value"</span><span class="special">&gt;&lt;</span><span class="identifier">child</span><span class="special">/&gt;&lt;/</span><span class="identifier">node</span><span class="special">&gt;</span>
-</pre>
-<div class="blockquote"><blockquote class="blockquote"><p>
- There are two element nodes here: one has name <code class="computeroutput"><span class="string">"node"</span></code>,
- single attribute <code class="computeroutput"><span class="string">"attr"</span></code>
- and single child <code class="computeroutput"><span class="string">"child"</span></code>,
- another has name <code class="computeroutput"><span class="string">"child"</span></code>
- and does not have any attributes or child nodes.
- </p></blockquote></div>
-<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">
- Plain character data nodes (<a name="node_pcdata"></a><code class="literal">node_pcdata</code>)
- represent plain text in XML. PCDATA nodes have a value, but do not have
- a name or children/attributes. Note that <span class="bold"><strong>plain
- character data is not a part of the element node but instead has its
- own node</strong></span>; an element node can have several child PCDATA nodes.
- The example XML representation of text nodes is as follows:
- </li></ul></div>
-<pre class="programlisting"><span class="special">&lt;</span><span class="identifier">node</span><span class="special">&gt;</span> <span class="identifier">text1</span> <span class="special">&lt;</span><span class="identifier">child</span><span class="special">/&gt;</span> <span class="identifier">text2</span> <span class="special">&lt;/</span><span class="identifier">node</span><span class="special">&gt;</span>
-</pre>
-<div class="blockquote"><blockquote class="blockquote"><p>
- Here <code class="computeroutput"><span class="string">"node"</span></code> element
- has three children, two of which are PCDATA nodes with values <code class="computeroutput"><span class="string">" text1 "</span></code> and <code class="computeroutput"><span class="string">"
- text2 "</span></code>.
- </p></blockquote></div>
-<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">
- Character data nodes (<a name="node_cdata"></a><code class="literal">node_cdata</code>) represent
- text in XML that is quoted in a special way. CDATA nodes do not differ
- from PCDATA nodes except in XML representation - the above text example
- looks like this with CDATA:
- </li></ul></div>
-<pre class="programlisting"><span class="special">&lt;</span><span class="identifier">node</span><span class="special">&gt;</span> <span class="special">&lt;![</span><span class="identifier">CDATA</span><span class="special">[[</span><span class="identifier">text1</span><span class="special">]]&gt;</span> <span class="special">&lt;</span><span class="identifier">child</span><span class="special">/&gt;</span> <span class="special">&lt;![</span><span class="identifier">CDATA</span><span class="special">[[</span><span class="identifier">text2</span><span class="special">]]&gt;</span> <span class="special">&lt;/</span><span class="identifier">node</span><span class="special">&gt;</span>
-</pre>
-<div class="blockquote"><blockquote class="blockquote"><p>
- CDATA nodes make it easy to include non-escaped &lt;, &amp; and &gt; characters
- in plain text. CDATA value can not contain the character sequence ]]&gt;,
- since it is used to determine the end of node contents.
- </p></blockquote></div>
-<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">
- Comment nodes (<a name="node_comment"></a><code class="literal">node_comment</code>) represent
- comments in XML. Comment nodes have a value, but do not have a name or
- children/attributes. The example XML representation of a comment node
- is as follows:
- </li></ul></div>
-<pre class="programlisting"><span class="special">&lt;!--</span> <span class="identifier">comment</span> <span class="identifier">text</span> <span class="special">--&gt;</span>
-</pre>
-<div class="blockquote"><blockquote class="blockquote"><p>
- Here the comment node has value <code class="computeroutput"><span class="string">"comment
- text"</span></code>. By default comment nodes are treated as non-essential
- part of XML markup and are not loaded during XML parsing. You can override
- this behavior with <a class="link" href="loading.html#parse_comments">parse_comments</a>
- flag.
- </p></blockquote></div>
-<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">
- Processing instruction node (<a name="node_pi"></a><code class="literal">node_pi</code>) represent
- processing instructions (PI) in XML. PI nodes have a name and an optional
- value, but do not have children/attributes. The example XML representation
- of a PI node is as follows:
- </li></ul></div>
-<pre class="programlisting"><span class="special">&lt;?</span><span class="identifier">name</span> <span class="identifier">value</span><span class="special">?&gt;</span>
-</pre>
-<div class="blockquote"><blockquote class="blockquote"><p>
- Here the name (also called PI target) is <code class="computeroutput"><span class="string">"name"</span></code>,
- and the value is <code class="computeroutput"><span class="string">"value"</span></code>.
- By default PI nodes are treated as non-essential part of XML markup and
- are not loaded during XML parsing. You can override this behavior with
- <a class="link" href="loading.html#parse_pi">parse_pi</a> flag.
- </p></blockquote></div>
-<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">
- Declaration node (<a name="node_declaration"></a><code class="literal">node_declaration</code>)
- represents document declarations in XML. Declaration nodes have a name
- (<code class="computeroutput"><span class="string">"xml"</span></code>) and an
- optional collection of attributes, but do not have value or children.
- There can be only one declaration node in a document; moreover, it should
- be the topmost node (its parent should be the document). The example
- XML representation of a declaration node is as follows:
- </li></ul></div>
-<pre class="programlisting"><span class="special">&lt;?</span><span class="identifier">xml</span> <span class="identifier">version</span><span class="special">=</span><span class="string">"1.0"</span><span class="special">?&gt;</span>
-</pre>
-<div class="blockquote"><blockquote class="blockquote"><p>
- Here the node has name <code class="computeroutput"><span class="string">"xml"</span></code>
- and a single attribute with name <code class="computeroutput"><span class="string">"version"</span></code>
- and value <code class="computeroutput"><span class="string">"1.0"</span></code>.
- By default declaration nodes are treated as non-essential part of XML markup
- and are not loaded during XML parsing. You can override this behavior with
- <a class="link" href="loading.html#parse_declaration">parse_declaration</a> flag. Also,
- by default a dummy declaration is output when XML document is saved unless
- there is already a declaration in the document; you can disable this with
- <a class="link" href="saving.html#format_no_declaration">format_no_declaration</a> flag.
- </p></blockquote></div>
-<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">
- Document type declaration node (<a name="node_doctype"></a><code class="literal">node_doctype</code>)
- represents document type declarations in XML. Document type declaration
- nodes have a value, which corresponds to the entire document type contents;
- no additional nodes are created for inner elements like <code class="computeroutput"><span class="special">&lt;!</span><span class="identifier">ENTITY</span><span class="special">&gt;</span></code>. There can be only one document type
- declaration node in a document; moreover, it should be the topmost node
- (its parent should be the document). The example XML representation of
- a document type declaration node is as follows:
- </li></ul></div>
-<pre class="programlisting"><span class="special">&lt;!</span><span class="identifier">DOCTYPE</span> <span class="identifier">greeting</span> <span class="special">[</span> <span class="special">&lt;!</span><span class="identifier">ELEMENT</span> <span class="identifier">greeting</span> <span class="special">(</span><span class="preprocessor">#PCDATA</span><span class="special">)&gt;</span> <span class="special">]&gt;</span>
-</pre>
-<div class="blockquote"><blockquote class="blockquote"><p>
- Here the node has value <code class="computeroutput"><span class="string">"greeting [ &lt;!ELEMENT
- greeting (#PCDATA)&gt; ]"</span></code>. By default document type
- declaration nodes are treated as non-essential part of XML markup and are
- not loaded during XML parsing. You can override this behavior with <a class="link" href="loading.html#parse_doctype">parse_doctype</a> flag.
- </p></blockquote></div>
-<p>
- Finally, here is a complete example of XML document and the corresponding
- tree representation (<a href="../samples/tree.xml" target="_top">samples/tree.xml</a>):
- </p>
-<div class="informaltable"><table class="table">
-<colgroup>
-<col>
-<col>
-</colgroup>
-<tbody><tr>
-<td>
- <p>
-
-</p>
-<pre xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" class="table-programlisting"><span class="special">&lt;?</span><span class="identifier">xml</span> <span class="identifier">version</span><span class="special">=</span><span class="string">"1.0"</span><span class="special">?&gt;</span>
-<span class="special">&lt;</span><span class="identifier">mesh</span> <span class="identifier">name</span><span class="special">=</span><span class="string">"mesh_root"</span><span class="special">&gt;</span>
- <span class="special">&lt;!--</span> <span class="identifier">here</span> <span class="identifier">is</span> <span class="identifier">a</span> <span class="identifier">mesh</span> <span class="identifier">node</span> <span class="special">--&gt;</span>
- <span class="identifier">some</span> <span class="identifier">text</span>
- <span class="special">&lt;![</span><span class="identifier">CDATA</span><span class="special">[</span><span class="identifier">someothertext</span><span class="special">]]&gt;</span>
- <span class="identifier">some</span> <span class="identifier">more</span> <span class="identifier">text</span>
- <span class="special">&lt;</span><span class="identifier">node</span> <span class="identifier">attr1</span><span class="special">=</span><span class="string">"value1"</span> <span class="identifier">attr2</span><span class="special">=</span><span class="string">"value2"</span> <span class="special">/&gt;</span>
- <span class="special">&lt;</span><span class="identifier">node</span> <span class="identifier">attr1</span><span class="special">=</span><span class="string">"value2"</span><span class="special">&gt;</span>
- <span class="special">&lt;</span><span class="identifier">innernode</span><span class="special">/&gt;</span>
- <span class="special">&lt;/</span><span class="identifier">node</span><span class="special">&gt;</span>
-<span class="special">&lt;/</span><span class="identifier">mesh</span><span class="special">&gt;</span>
-<span class="special">&lt;?</span><span class="identifier">include</span> <span class="identifier">somedata</span><span class="special">?&gt;</span>
-</pre>
-<p>
- </p>
- </td>
-<td>
- <p>
- <a href="../images/dom_tree.png" target="_top"><span class="inlinemediaobject"><img src="../images/dom_tree_thumb.png" alt="dom_tree_thumb"></span></a>
- </p>
- </td>
-</tr></tbody>
-</table></div>
-</div>
-<div class="section">
-<div class="titlepage"><div><div><h3 class="title">
-<a name="manual.dom.cpp"></a><a class="link" href="dom.html#manual.dom.cpp" title="C++ interface"> C++ interface</a>
-</h3></div></div></div>
-<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>
- All pugixml classes and functions are located in the <code class="computeroutput"><span class="identifier">pugi</span></code>
- namespace; you have to either use explicit name qualification (i.e. <code class="computeroutput"><span class="identifier">pugi</span><span class="special">::</span><span class="identifier">xml_node</span></code>), or to gain access to relevant
- symbols via <code class="computeroutput"><span class="keyword">using</span></code> directive
- (i.e. <code class="computeroutput"><span class="keyword">using</span> <span class="identifier">pugi</span><span class="special">::</span><span class="identifier">xml_node</span><span class="special">;</span></code> or <code class="computeroutput"><span class="keyword">using</span>
- <span class="keyword">namespace</span> <span class="identifier">pugi</span><span class="special">;</span></code>). The namespace will be omitted from all
- declarations in this documentation hereafter; all code examples will use
- fully qualified names.
- </p></td></tr>
-</table></div>
-<p>
- Despite the fact that there are several node types, there are only three
- C++ classes representing the tree (<code class="computeroutput"><span class="identifier">xml_document</span></code>,
- <code class="computeroutput"><span class="identifier">xml_node</span></code>, <code class="computeroutput"><span class="identifier">xml_attribute</span></code>);
- some operations on <code class="computeroutput"><span class="identifier">xml_node</span></code>
- are only valid for certain node types. The classes are described below.
- </p>
-<a name="xml_document"></a><a name="xml_document::document_element"></a><p>
- <code class="computeroutput"><span class="identifier">xml_document</span></code> is the owner
- of the entire document structure; it is a non-copyable class. The interface
- of <code class="computeroutput"><span class="identifier">xml_document</span></code> consists
- of loading functions (see <a class="xref" href="loading.html" title="Loading document"> Loading document</a>), saving functions (see <a class="xref" href="saving.html" title="Saving document"> Saving document</a>)
- and the entire interface of <code class="computeroutput"><span class="identifier">xml_node</span></code>,
- which allows for document inspection and/or modification. Note that while
- <code class="computeroutput"><span class="identifier">xml_document</span></code> is a sub-class
- of <code class="computeroutput"><span class="identifier">xml_node</span></code>, <code class="computeroutput"><span class="identifier">xml_node</span></code> is not a polymorphic type; the
- inheritance is present only to simplify usage. Alternatively you can use
- the <code class="computeroutput"><span class="identifier">document_element</span></code> function
- to get the element node that's the immediate child of the document.
- </p>
-<a name="xml_document::ctor"></a><a name="xml_document::dtor"></a><a name="xml_document::reset"></a><p>
- Default constructor of <code class="computeroutput"><span class="identifier">xml_document</span></code>
- initializes the document to the tree with only a root node (document node).
- You can then populate it with data using either tree modification functions
- or loading functions; all loading functions destroy the previous tree with
- all occupied memory, which puts existing node/attribute handles for this
- document to invalid state. If you want to destroy the previous tree, you
- can use the <code class="computeroutput"><span class="identifier">xml_document</span><span class="special">::</span><span class="identifier">reset</span></code>
- function; it destroys the tree and replaces it with either an empty one or
- a copy of the specified document. Destructor of <code class="computeroutput"><span class="identifier">xml_document</span></code>
- also destroys the tree, thus the lifetime of the document object should exceed
- the lifetimes of any node/attribute handles that point to the tree.
- </p>
-<div class="caution"><table border="0" summary="Caution">
-<tr>
-<td rowspan="2" align="center" valign="top" width="25"><img alt="[Caution]" src="../images/caution.png"></td>
-<th align="left">Caution</th>
-</tr>
-<tr><td align="left" valign="top"><p>
- While technically node/attribute handles can be alive when the tree they're
- referring to is destroyed, calling any member function for these handles
- results in undefined behavior. Thus it is recommended to make sure that
- the document is destroyed only after all references to its nodes/attributes
- are destroyed.
- </p></td></tr>
-</table></div>
-<a name="xml_node"></a><a name="xml_node::type"></a><p>
- <code class="computeroutput"><span class="identifier">xml_node</span></code> is the handle to
- document node; it can point to any node in the document, including the document
- node itself. There is a common interface for nodes of all types; the actual
- <a class="link" href="dom.html#xml_node_type">node type</a> can be queried via the <code class="computeroutput"><span class="identifier">xml_node</span><span class="special">::</span><span class="identifier">type</span><span class="special">()</span></code>
- method. Note that <code class="computeroutput"><span class="identifier">xml_node</span></code>
- is only a handle to the actual node, not the node itself - you can have several
- <code class="computeroutput"><span class="identifier">xml_node</span></code> handles pointing
- to the same underlying object. Destroying <code class="computeroutput"><span class="identifier">xml_node</span></code>
- handle does not destroy the node and does not remove it from the tree. The
- size of <code class="computeroutput"><span class="identifier">xml_node</span></code> is equal
- to that of a pointer, so it is nothing more than a lightweight wrapper around
- a pointer; you can safely pass or return <code class="computeroutput"><span class="identifier">xml_node</span></code>
- objects by value without additional overhead.
- </p>
-<a name="node_null"></a><p>
- There is a special value of <code class="computeroutput"><span class="identifier">xml_node</span></code>
- type, known as null node or empty node (such nodes have type <code class="computeroutput"><span class="identifier">node_null</span></code>). It does not correspond to any
- node in any document, and thus resembles null pointer. However, all operations
- are defined on empty nodes; generally the operations don't do anything and
- return empty nodes/attributes or empty strings as their result (see documentation
- for specific functions for more detailed information). This is useful for
- chaining calls; i.e. you can get the grandparent of a node like so: <code class="computeroutput"><span class="identifier">node</span><span class="special">.</span><span class="identifier">parent</span><span class="special">().</span><span class="identifier">parent</span><span class="special">()</span></code>; if a node is a null node or it does not
- have a parent, the first <code class="computeroutput"><span class="identifier">parent</span><span class="special">()</span></code> call returns null node; the second <code class="computeroutput"><span class="identifier">parent</span><span class="special">()</span></code>
- call then also returns null node, which makes error handling easier.
- </p>
-<a name="xml_attribute"></a><p>
- <code class="computeroutput"><span class="identifier">xml_attribute</span></code> is the handle
- to an XML attribute; it has the same semantics as <code class="computeroutput"><span class="identifier">xml_node</span></code>,
- i.e. there can be several <code class="computeroutput"><span class="identifier">xml_attribute</span></code>
- handles pointing to the same underlying object and there is a special null
- attribute value, which propagates to function results.
- </p>
-<a name="xml_attribute::ctor"></a><a name="xml_node::ctor"></a><p>
- Both <code class="computeroutput"><span class="identifier">xml_node</span></code> and <code class="computeroutput"><span class="identifier">xml_attribute</span></code> have the default constructor
- which initializes them to null objects.
- </p>
-<a name="xml_attribute::comparison"></a><a name="xml_node::comparison"></a><p>
- <code class="computeroutput"><span class="identifier">xml_node</span></code> and <code class="computeroutput"><span class="identifier">xml_attribute</span></code> try to behave like pointers,
- that is, they can be compared with other objects of the same type, making
- it possible to use them as keys in associative containers. All handles to
- the same underlying object are equal, and any two handles to different underlying
- objects are not equal. Null handles only compare as equal to themselves.
- The result of relational comparison can not be reliably determined from the
- order of nodes in file or in any other way. Do not use relational comparison
- operators except for search optimization (i.e. associative container keys).
- </p>
-<a name="xml_attribute::hash_value"></a><a name="xml_node::hash_value"></a><p>
- If you want to use <code class="computeroutput"><span class="identifier">xml_node</span></code>
- or <code class="computeroutput"><span class="identifier">xml_attribute</span></code> objects
- as keys in hash-based associative containers, you can use the <code class="computeroutput"><span class="identifier">hash_value</span></code> member functions. They return
- the hash values that are guaranteed to be the same for all handles to the
- same underlying object. The hash value for null handles is 0.
- </p>
-<a name="xml_attribute::unspecified_bool_type"></a><a name="xml_node::unspecified_bool_type"></a><a name="xml_attribute::empty"></a><a name="xml_node::empty"></a><p>
- Finally handles can be implicitly cast to boolean-like objects, so that you
- can test if the node/attribute is empty with the following code: <code class="computeroutput"><span class="keyword">if</span> <span class="special">(</span><span class="identifier">node</span><span class="special">)</span> <span class="special">{</span> <span class="special">...</span>
- <span class="special">}</span></code> or <code class="computeroutput"><span class="keyword">if</span>
- <span class="special">(!</span><span class="identifier">node</span><span class="special">)</span> <span class="special">{</span> <span class="special">...</span>
- <span class="special">}</span> <span class="keyword">else</span> <span class="special">{</span> <span class="special">...</span> <span class="special">}</span></code>.
- Alternatively you can check if a given <code class="computeroutput"><span class="identifier">xml_node</span></code>/<code class="computeroutput"><span class="identifier">xml_attribute</span></code> handle is null by calling
- the following methods:
- </p>
-<pre class="programlisting"><span class="keyword">bool</span> <span class="identifier">xml_attribute</span><span class="special">::</span><span class="identifier">empty</span><span class="special">()</span> <span class="keyword">const</span><span class="special">;</span>
-<span class="keyword">bool</span> <span class="identifier">xml_node</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>
- Nodes and attributes do not exist without a document tree, so you can't create
- them without adding them to some document. Once underlying node/attribute
- objects are destroyed, the handles to those objects become invalid. While
- this means that destruction of the entire tree invalidates all node/attribute
- handles, it also means that destroying a subtree (by calling <a class="link" href="modify.html#xml_node::remove_child">xml_node::remove_child</a>)
- or removing an attribute invalidates the corresponding handles. There is
- no way to check handle validity; you have to ensure correctness through external
- mechanisms.
- </p>
-</div>
-<div class="section">
-<div class="titlepage"><div><div><h3 class="title">
-<a name="manual.dom.unicode"></a><a class="link" href="dom.html#manual.dom.unicode" title="Unicode interface"> Unicode interface</a>
-</h3></div></div></div>
-<p>
- There are two choices of interface and internal representation when configuring
- pugixml: you can either choose the UTF-8 (also called char) interface or
- UTF-16/32 (also called wchar_t) one. The choice is controlled via <a class="link" href="install.html#PUGIXML_WCHAR_MODE">PUGIXML_WCHAR_MODE</a>
- define; you can set it via <code class="filename">pugiconfig.hpp</code> or via preprocessor options, as
- discussed in <a class="xref" href="install.html#manual.install.building.config" title="Additional configuration options"> Additional configuration
- options</a>. If this define is set, the wchar_t
- interface is used; otherwise (by default) the char interface is used. The
- exact wide character encoding is assumed to be either UTF-16 or UTF-32 and
- is determined based on the size of <code class="computeroutput"><span class="keyword">wchar_t</span></code>
- type.
- </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>
- If the size of <code class="computeroutput"><span class="keyword">wchar_t</span></code> is
- 2, pugixml assumes UTF-16 encoding instead of UCS-2, which means that some
- characters are represented as two code points.
- </p></td></tr>
-</table></div>
-<p>
- All tree functions that work with strings work with either C-style null terminated
- strings or STL strings of the selected character type. For example, node
- name accessors look like this in char mode:
- </p>
-<pre class="programlisting"><span class="keyword">const</span> <span class="keyword">char</span><span class="special">*</span> <span class="identifier">xml_node</span><span class="special">::</span><span class="identifier">name</span><span class="special">()</span> <span class="keyword">const</span><span class="special">;</span>
-<span class="keyword">bool</span> <span class="identifier">xml_node</span><span class="special">::</span><span class="identifier">set_name</span><span class="special">(</span><span class="keyword">const</span> <span class="keyword">char</span><span class="special">*</span> <span class="identifier">value</span><span class="special">);</span>
-</pre>
-<p>
- and like this in wchar_t mode:
- </p>
-<pre class="programlisting"><span class="keyword">const</span> <span class="keyword">wchar_t</span><span class="special">*</span> <span class="identifier">xml_node</span><span class="special">::</span><span class="identifier">name</span><span class="special">()</span> <span class="keyword">const</span><span class="special">;</span>
-<span class="keyword">bool</span> <span class="identifier">xml_node</span><span class="special">::</span><span class="identifier">set_name</span><span class="special">(</span><span class="keyword">const</span> <span class="keyword">wchar_t</span><span class="special">*</span> <span class="identifier">value</span><span class="special">);</span>
-</pre>
-<a name="char_t"></a><a name="string_t"></a><p>
- There is a special type, <code class="computeroutput"><span class="identifier">pugi</span><span class="special">::</span><span class="identifier">char_t</span></code>,
- that is defined as the character type and depends on the library configuration;
- it will be also used in the documentation hereafter. There is also a type
- <code class="computeroutput"><span class="identifier">pugi</span><span class="special">::</span><span class="identifier">string_t</span></code>, which is defined as the STL string
- of the character type; it corresponds to <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span></code>
- in char mode and to <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">wstring</span></code> in wchar_t mode.
- </p>
-<p>
- In addition to the interface, the internal implementation changes to store
- XML data as <code class="computeroutput"><span class="identifier">pugi</span><span class="special">::</span><span class="identifier">char_t</span></code>; this means that these two modes
- have different memory usage characteristics. The conversion to <code class="computeroutput"><span class="identifier">pugi</span><span class="special">::</span><span class="identifier">char_t</span></code> upon document loading and from
- <code class="computeroutput"><span class="identifier">pugi</span><span class="special">::</span><span class="identifier">char_t</span></code> upon document saving happen automatically,
- which also carries minor performance penalty. The general advice however
- is to select the character mode based on usage scenario, i.e. if UTF-8 is
- inconvenient to process and most of your XML data is non-ASCII, wchar_t mode
- is probably a better choice.
- </p>
-<a name="as_utf8"></a><a name="as_wide"></a><p>
- There are cases when you'll have to convert string data between UTF-8 and
- wchar_t encodings; the following helper functions are provided for such purposes:
- </p>
-<pre class="programlisting"><span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span> <span class="identifier">as_utf8</span><span class="special">(</span><span class="keyword">const</span> <span class="keyword">wchar_t</span><span class="special">*</span> <span class="identifier">str</span><span class="special">);</span>
-<span class="identifier">std</span><span class="special">::</span><span class="identifier">wstring</span> <span class="identifier">as_wide</span><span class="special">(</span><span class="keyword">const</span> <span class="keyword">char</span><span class="special">*</span> <span class="identifier">str</span><span class="special">);</span>
-</pre>
-<p>
- Both functions accept a null-terminated string as an argument <code class="computeroutput"><span class="identifier">str</span></code>, and return the converted string.
- <code class="computeroutput"><span class="identifier">as_utf8</span></code> performs conversion
- from UTF-16/32 to UTF-8; <code class="computeroutput"><span class="identifier">as_wide</span></code>
- performs conversion from UTF-8 to UTF-16/32. Invalid UTF sequences are silently
- discarded upon conversion. <code class="computeroutput"><span class="identifier">str</span></code>
- has to be a valid string; passing null pointer results in undefined behavior.
- There are also two overloads with the same semantics which accept a string
- as an argument:
- </p>
-<pre class="programlisting"><span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span> <span class="identifier">as_utf8</span><span class="special">(</span><span class="keyword">const</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">wstring</span><span class="special">&amp;</span> <span class="identifier">str</span><span class="special">);</span>
-<span class="identifier">std</span><span class="special">::</span><span class="identifier">wstring</span> <span class="identifier">as_wide</span><span class="special">(</span><span class="keyword">const</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span><span class="special">&amp;</span> <span class="identifier">str</span><span class="special">);</span>
-</pre>
-<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>
- Most examples in this documentation assume char interface and therefore
- will not compile with <a class="link" href="install.html#PUGIXML_WCHAR_MODE">PUGIXML_WCHAR_MODE</a>.
- This is done to simplify the documentation; usually the only changes you'll
- have to make is to pass <code class="computeroutput"><span class="keyword">wchar_t</span></code>
- string literals, i.e. instead of
- </p>
-<p>
- <code class="computeroutput"><span class="identifier">pugi</span><span class="special">::</span><span class="identifier">xml_node</span> <span class="identifier">node</span>
- <span class="special">=</span> <span class="identifier">doc</span><span class="special">.</span><span class="identifier">child</span><span class="special">(</span><span class="string">"bookstore"</span><span class="special">).</span><span class="identifier">find_child_by_attribute</span><span class="special">(</span><span class="string">"book"</span><span class="special">,</span> <span class="string">"id"</span><span class="special">,</span> <span class="string">"12345"</span><span class="special">);</span></code>
- </p>
-<p>
- you'll have to do
- </p>
-<p>
- <code class="computeroutput"><span class="identifier">pugi</span><span class="special">::</span><span class="identifier">xml_node</span> <span class="identifier">node</span>
- <span class="special">=</span> <span class="identifier">doc</span><span class="special">.</span><span class="identifier">child</span><span class="special">(</span><span class="identifier">L</span><span class="string">"bookstore"</span><span class="special">).</span><span class="identifier">find_child_by_attribute</span><span class="special">(</span><span class="identifier">L</span><span class="string">"book"</span><span class="special">,</span> <span class="identifier">L</span><span class="string">"id"</span><span class="special">,</span> <span class="identifier">L</span><span class="string">"12345"</span><span class="special">);</span></code>
- </p>
-</td></tr>
-</table></div>
-</div>
-<div class="section">
-<div class="titlepage"><div><div><h3 class="title">
-<a name="manual.dom.thread"></a><a class="link" href="dom.html#manual.dom.thread" title="Thread-safety guarantees"> Thread-safety guarantees</a>
-</h3></div></div></div>
-<p>
- Almost all functions in pugixml have the following thread-safety guarantees:
- </p>
-<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
-<li class="listitem">
- it is safe to call free (non-member) functions from multiple threads
- </li>
-<li class="listitem">
- it is safe to perform concurrent read-only accesses to the same tree
- (all constant member functions do not modify the tree)
- </li>
-<li class="listitem">
- it is safe to perform concurrent read/write accesses, if there is only
- one read or write access to the single tree at a time
- </li>
-</ul></div>
-<p>
- Concurrent modification and traversing of a single tree requires synchronization,
- for example via reader-writer lock. Modification includes altering document
- structure and altering individual node/attribute data, i.e. changing names/values.
- </p>
-<p>
- The only exception is <a class="link" href="dom.html#set_memory_management_functions">set_memory_management_functions</a>;
- it modifies global variables and as such is not thread-safe. Its usage policy
- has more restrictions, see <a class="xref" href="dom.html#manual.dom.memory.custom" title="Custom memory allocation/deallocation functions"> Custom memory allocation/deallocation
- functions</a>.
- </p>
-</div>
-<div class="section">
-<div class="titlepage"><div><div><h3 class="title">
-<a name="manual.dom.exception"></a><a class="link" href="dom.html#manual.dom.exception" title="Exception guarantees"> Exception guarantees</a>
-</h3></div></div></div>
-<p>
- With the exception of XPath, pugixml itself does not throw any exceptions.
- Additionally, most pugixml functions have a no-throw exception guarantee.
- </p>
-<p>
- This is not applicable to functions that operate on STL strings or IOstreams;
- such functions have either strong guarantee (functions that operate on strings)
- or basic guarantee (functions that operate on streams). Also functions that
- call user-defined callbacks (i.e. <a class="link" href="access.html#xml_node::traverse">xml_node::traverse</a>
- or <a class="link" href="access.html#xml_node::find_node">xml_node::find_node</a>) do not
- provide any exception guarantees beyond the ones provided by the callback.
- </p>
-<p>
- If exception handling is not disabled with <a class="link" href="install.html#PUGIXML_NO_EXCEPTIONS">PUGIXML_NO_EXCEPTIONS</a>
- define, XPath functions may throw <a class="link" href="xpath.html#xpath_exception">xpath_exception</a>
- on parsing errors; also, XPath functions may throw <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">bad_alloc</span></code>
- in low memory conditions. Still, XPath functions provide strong exception
- guarantee.
- </p>
-</div>
-<div class="section">
-<div class="titlepage"><div><div><h3 class="title">
-<a name="manual.dom.memory"></a><a class="link" href="dom.html#manual.dom.memory" title="Memory management"> Memory management</a>
-</h3></div></div></div>
-<p>
- pugixml requests the memory needed for document storage in big chunks, and
- allocates document data inside those chunks. This section discusses replacing
- functions used for chunk allocation and internal memory management implementation.
- </p>
-<div class="section">
-<div class="titlepage"><div><div><h4 class="title">
-<a name="manual.dom.memory.custom"></a><a class="link" href="dom.html#manual.dom.memory.custom" title="Custom memory allocation/deallocation functions"> Custom memory allocation/deallocation
- functions</a>
-</h4></div></div></div>
-<a name="allocation_function"></a><a name="deallocation_function"></a><p>
- All memory for tree structure, tree data and XPath objects is allocated
- via globally specified functions, which default to malloc/free. You can
- set your own allocation functions with set_memory_management function.
- The function interfaces are the same as that of malloc/free:
- </p>
-<pre class="programlisting"><span class="keyword">typedef</span> <span class="keyword">void</span><span class="special">*</span> <span class="special">(*</span><span class="identifier">allocation_function</span><span class="special">)(</span><span class="identifier">size_t</span> <span class="identifier">size</span><span class="special">);</span>
-<span class="keyword">typedef</span> <span class="keyword">void</span> <span class="special">(*</span><span class="identifier">deallocation_function</span><span class="special">)(</span><span class="keyword">void</span><span class="special">*</span> <span class="identifier">ptr</span><span class="special">);</span>
-</pre>
-<a name="set_memory_management_functions"></a><a name="get_memory_allocation_function"></a><a name="get_memory_deallocation_function"></a><p>
- You can use the following accessor functions to change or get current memory
- management functions:
- </p>
-<pre class="programlisting"><span class="keyword">void</span> <span class="identifier">set_memory_management_functions</span><span class="special">(</span><span class="identifier">allocation_function</span> <span class="identifier">allocate</span><span class="special">,</span> <span class="identifier">deallocation_function</span> <span class="identifier">deallocate</span><span class="special">);</span>
-<span class="identifier">allocation_function</span> <span class="identifier">get_memory_allocation_function</span><span class="special">();</span>
-<span class="identifier">deallocation_function</span> <span class="identifier">get_memory_deallocation_function</span><span class="special">();</span>
-</pre>
-<p>
- Allocation function is called with the size (in bytes) as an argument and
- should return a pointer to a memory block with alignment that is suitable
- for storage of primitive types (usually a maximum of <code class="computeroutput"><span class="keyword">void</span><span class="special">*</span></code> and <code class="computeroutput"><span class="keyword">double</span></code>
- types alignment is sufficient) and size that is greater than or equal to
- the requested one. If the allocation fails, the function has to return
- null pointer (throwing an exception from allocation function results in
- undefined behavior).
- </p>
-<p>
- Deallocation function is called with the pointer that was returned by some
- call to allocation function; it is never called with a null pointer. If
- memory management functions are not thread-safe, library thread safety
- is not guaranteed.
- </p>
-<p>
- This is a simple example of custom memory management (<a href="../samples/custom_memory_management.cpp" target="_top">samples/custom_memory_management.cpp</a>):
- </p>
-<p>
-
-</p>
-<pre class="programlisting"><span class="keyword">void</span><span class="special">*</span> <span class="identifier">custom_allocate</span><span class="special">(</span><span class="identifier">size_t</span> <span class="identifier">size</span><span class="special">)</span>
-<span class="special">{</span>
- <span class="keyword">return</span> <span class="keyword">new</span> <span class="special">(</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">nothrow</span><span class="special">)</span> <span class="keyword">char</span><span class="special">[</span><span class="identifier">size</span><span class="special">];</span>
-<span class="special">}</span>
-
-<span class="keyword">void</span> <span class="identifier">custom_deallocate</span><span class="special">(</span><span class="keyword">void</span><span class="special">*</span> <span class="identifier">ptr</span><span class="special">)</span>
-<span class="special">{</span>
- <span class="keyword">delete</span><span class="special">[]</span> <span class="keyword">static_cast</span><span class="special">&lt;</span><span class="keyword">char</span><span class="special">*&gt;(</span><span class="identifier">ptr</span><span class="special">);</span>
-<span class="special">}</span>
-</pre>
-<p>
- </p>
-<p>
-
-</p>
-<pre class="programlisting"><span class="identifier">pugi</span><span class="special">::</span><span class="identifier">set_memory_management_functions</span><span class="special">(</span><span class="identifier">custom_allocate</span><span class="special">,</span> <span class="identifier">custom_deallocate</span><span class="special">);</span>
-</pre>
-<p>
- </p>
-<p>
- When setting new memory management functions, care must be taken to make
- sure that there are no live pugixml objects. Otherwise when the objects
- are destroyed, the new deallocation function will be called with the memory
- obtained by the old allocation function, resulting in undefined behavior.
- </p>
-</div>
-<div class="section">
-<div class="titlepage"><div><div><h4 class="title">
-<a name="manual.dom.memory.tuning"></a><a class="link" href="dom.html#manual.dom.memory.tuning" title="Memory consumption tuning"> Memory consumption tuning</a>
-</h4></div></div></div>
-<p>
- There are several important buffering optimizations in pugixml that rely
- on predefined constants. These constants have default values that were
- tuned for common usage patterns; for some applications, changing these
- constants might improve memory consumption or increase performance. Changing
- these constants is not recommended unless their default values result in
- visible problems.
- </p>
-<p>
- These constants can be tuned via configuration defines, as discussed in
- <a class="xref" href="install.html#manual.install.building.config" title="Additional configuration options"> Additional configuration
- options</a>; it is recommended to set them in <code class="filename">pugiconfig.hpp</code>.
- </p>
-<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
-<li class="listitem">
- <code class="computeroutput"><span class="identifier">PUGIXML_MEMORY_PAGE_SIZE</span></code>
- controls the page size for document memory allocation. Memory for node/attribute
- objects is allocated in pages of the specified size. The default size
- is 32 Kb; for some applications the size is too large (i.e. embedded
- systems with little heap space or applications that keep lots of XML
- documents in memory). A minimum size of 1 Kb is recommended. <br><br>
-
- </li>
-<li class="listitem">
- <code class="computeroutput"><span class="identifier">PUGIXML_MEMORY_OUTPUT_STACK</span></code>
- controls the cumulative stack space required to output the node. Any
- output operation (i.e. saving a subtree to file) uses an internal buffering
- scheme for performance reasons. The default size is 10 Kb; if you're
- using node output from threads with little stack space, decreasing
- this value can prevent stack overflows. A minimum size of 1 Kb is recommended.
- <br><br>
-
- </li>
-<li class="listitem">
- <code class="computeroutput"><span class="identifier">PUGIXML_MEMORY_XPATH_PAGE_SIZE</span></code>
- controls the page size for XPath memory allocation. Memory for XPath
- query objects as well as internal memory for XPath evaluation is allocated
- in pages of the specified size. The default size is 4 Kb; if you have
- a lot of resident XPath query objects, you might need to decrease the
- size to improve memory consumption. A minimum size of 256 bytes is
- recommended.
- </li>
-</ul></div>
-</div>
-<div class="section">
-<div class="titlepage"><div><div><h4 class="title">
-<a name="manual.dom.memory.internals"></a><a class="link" href="dom.html#manual.dom.memory.internals" title="Document memory management internals"> Document memory management
- internals</a>
-</h4></div></div></div>
-<p>
- Constructing a document object using the default constructor does not result
- in any allocations; document node is stored inside the <a class="link" href="dom.html#xml_document">xml_document</a>
- object.
- </p>
-<p>
- When the document is loaded from file/buffer, unless an inplace loading
- function is used (see <a class="xref" href="loading.html#manual.loading.memory" title="Loading document from memory"> Loading document from memory</a>), a complete copy of character
- stream is made; all names/values of nodes and attributes are allocated
- in this buffer. This buffer is allocated via a single large allocation
- and is only freed when document memory is reclaimed (i.e. if the <a class="link" href="dom.html#xml_document">xml_document</a> object is destroyed or if another
- document is loaded in the same object). Also when loading from file or
- stream, an additional large allocation may be performed if encoding conversion
- is required; a temporary buffer is allocated, and it is freed before load
- function returns.
- </p>
-<p>
- All additional memory, such as memory for document structure (node/attribute
- objects) and memory for node/attribute names/values is allocated in pages
- on the order of 32 kilobytes; actual objects are allocated inside the pages
- using a memory management scheme optimized for fast allocation/deallocation
- of many small objects. Because of the scheme specifics, the pages are only
- destroyed if all objects inside them are destroyed; also, generally destroying
- an object does not mean that subsequent object creation will reuse the
- same memory. This means that it is possible to devise a usage scheme which
- will lead to higher memory usage than expected; one example is adding a
- lot of nodes, and them removing all even numbered ones; not a single page
- is reclaimed in the process. However this is an example specifically crafted
- to produce unsatisfying behavior; in all practical usage scenarios the
- memory consumption is less than that of a general-purpose allocator because
- allocation meta-data is very small in size.
- </p>
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- Distributed under the MIT License
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