<?xml version="1.0" encoding="iso-8859-1"?>
<!DOCTYPE html
PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "DTD/xhtml1-strict.dtd">
<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en">
<!-- /tmp/qt-4.2.1-harald-1161357942206/qt-x11-opensource-src-4.2.1/src/corelib/tools/qhash.cpp -->
<head>
<title>Qt 4.2: QMultiHash Class Reference</title>
<link href="classic.css" rel="stylesheet" type="text/css" />
</head>
<body>
<table border="0" cellpadding="0" cellspacing="0" width="100%">
<tr>
<td align="left" valign="top" width="32"><a href="http://www.trolltech.com/products/qt"><img src="images/qt-logo.png" align="left" width="32" height="32" border="0" /></a></td>
<td width="1"> </td><td class="postheader" valign="center"><a href="index.html"><font color="#004faf">Home</font></a> · <a href="classes.html"><font color="#004faf">All Classes</font></a> · <a href="mainclasses.html"><font color="#004faf">Main Classes</font></a> · <a href="groups.html"><font color="#004faf">Grouped Classes</font></a> · <a href="modules.html"><font color="#004faf">Modules</font></a> · <a href="functions.html"><font color="#004faf">Functions</font></a></td>
<td align="right" valign="top" width="230"><a href="http://www.trolltech.com"><img src="images/trolltech-logo.png" align="right" width="203" height="32" border="0" /></a></td></tr></table><h1 align="center">QMultiHash Class Reference<br /><sup><sup>[<a href="qtcore.html">QtCore</a> module]</sup></sup></h1>
<p>The QMultiHash class is a convenience <a href="qhash.html">QHash</a> subclass that provides multi-valued hashes. <a href="#details">More...</a></p>
<pre> #include <QMultiHash></pre><p>Inherits <a href="qhash.html">QHash<Key, T></a>.</p>
<p><b>Note:</b> All the functions in this class are <a href="threads.html#reentrant">reentrant</a>.</p>
<ul>
<li><a href="qmultihash-members.html">List of all members, including inherited members</a></li>
</ul>
<a name="public-functions"></a>
<h3>Public Functions</h3>
<ul>
<li><div class="fn"/><b><a href="qmultihash.html#QMultiHash">QMultiHash</a></b> ()</li>
<li><div class="fn"/><b><a href="qmultihash.html#QMultiHash-2">QMultiHash</a></b> ( const QHash<Key, T> & <i>other</i> )</li>
<li><div class="fn"/>QHash<Key, T>::iterator <b><a href="qmultihash.html#insert">insert</a></b> ( const Key & <i>key</i>, const T & <i>value</i> )</li>
<li><div class="fn"/>QHash<Key, T>::iterator <b><a href="qmultihash.html#replace">replace</a></b> ( const Key & <i>key</i>, const T & <i>value</i> )</li>
<li><div class="fn"/>QMultiHash <b><a href="qmultihash.html#operator-2b">operator+</a></b> ( const QMultiHash & <i>other</i> ) const</li>
<li><div class="fn"/>QMultiHash & <b><a href="qmultihash.html#operator-2b-eq">operator+=</a></b> ( const QMultiHash & <i>other</i> )</li>
</ul>
<ul>
<li><div class="fn"/>38 public functions inherited from <a href="qhash.html#public-functions">QHash</a></li>
</ul>
<a name="details"></a>
<hr />
<h2>Detailed Description</h2>
<p>The QMultiHash class is a convenience <a href="qhash.html">QHash</a> subclass that provides multi-valued hashes.</p>
<p>QMultiHash<Key, T> is one of Qt's generic <a href="containers.html#container-classes">container classes</a>. It inherits <a href="qhash.html">QHash</a> and extends it with a few convenience functions that make it more suitable than <a href="qhash.html">QHash</a> for storing multi-valued hashes. A multi-valued hash is a hash that allows multiple values with the same key; <a href="qhash.html">QHash</a> normally doesn't allow that, unless you call <a href="qhash.html#insertMulti">QHash::insertMulti</a>().</p>
<p>Because QMultiHash inherits <a href="qhash.html">QHash</a>, all of <a href="qhash.html">QHash</a>'s functionality also applies to QMultiHash. For example, you can use <a href="qhash.html#isEmpty">isEmpty</a>() to test whether the hash is empty, and you can traverse a QMultiHash using <a href="qhash.html">QHash</a>'s iterator classes (for example, <a href="qhashiterator.html">QHashIterator</a>). But in addition, it provides an <a href="qmultihash.html#insert">insert</a>() function that corresponds to <a href="qhash.html#insertMulti">QHash::insertMulti</a>(), and a <a href="qmultihash.html#replace">replace</a>() function that corresponds to <a href="qhash.html#insert">QHash::insert</a>(). It also provides convenient operator+() and operator+=().</p>
<p>Example:</p>
<pre> QMultiHash<QString, int> hash1, hash2, hash3;
hash1.insert("plenty", 100);
hash1.insert("plenty", 2000);
<span class="comment"> // hash1.size() == 2</span>
hash2.insert("plenty", 5000);
<span class="comment"> // hash2.size() == 1</span>
hash3 = hash1 + hash2;
<span class="comment"> // hash3.size() == 3</span></pre>
<p>Unlike <a href="qhash.html">QHash</a>, QMultiHash provides no operator[]. Use <a href="qhash.html#value">value</a>() or <a href="qmultihash.html#replace">replace</a>() if you want to access the most recently inserted item with a certain key.</p>
<p>If you want to retrieve all the values for a single key, you can use values(const Key &key), which returns a <a href="qlist.html">QList</a><T>:</p>
<pre> QList<int> values = hash.values("plenty");
for (int i = 0; i < values.size(); ++i)
cout << values.at(i) << endl;</pre>
<p>The items that share the same key are available from most recently to least recently inserted.</p>
<p>A more efficient approach is to call <a href="qhash.html#find">find</a>() to get the STL-style iterator for the first item with a key and iterate from there:</p>
<pre> QMultiHash<QString, int>::iterator i = hash.find("plenty");
while (i != hash.end() && i.key() == "plenty") {
cout << i.value() << endl;
++i;
}</pre>
<p>QMultiHash's key and value data types must be <a href="containers.html#assignable-data-types">assignable data types</a>. You cannot, for example, store a <a href="qwidget.html">QWidget</a> as a value; instead, store a <a href="qwidget.html">QWidget</a> *. In addition, QMultiHash's key type must provide operator==(), and there must also be a global qHash() function that returns a hash value for an argument of the key's type. See the <a href="qhash.html">QHash</a> documentation for details.</p>
<p>See also <a href="qhash.html">QHash</a>, <a href="qhashiterator.html">QHashIterator</a>, <a href="qmutablehashiterator.html">QMutableHashIterator</a>, and <a href="qmultimap.html">QMultiMap</a>.</p>
<hr />
<h2>Member Function Documentation</h2>
<h3 class="fn"><a name="QMultiHash"></a>QMultiHash::QMultiHash ()</h3>
<p>Constructs an empty hash.</p>
<h3 class="fn"><a name="QMultiHash-2"></a>QMultiHash::QMultiHash ( const <a href="qhash.html">QHash</a><Key, T> & <i>other</i> )</h3>
<p>Constructs a copy of <i>other</i> (which can be a <a href="qhash.html">QHash</a> or a <a href="qmultihash.html">QMultiHash</a>).</p>
<p>See also <a href="qhash.html#operator-eq">operator=</a>().</p>
<h3 class="fn"><a name="insert"></a><a href="qhash.html">QHash</a><Key, T>::iterator QMultiHash::insert ( const Key & <i>key</i>, const T & <i>value</i> )</h3>
<p>Inserts a new item with the key <i>key</i> and a value of <i>value</i>.</p>
<p>If there is already an item with the same key in the hash, this function will simply create a new one. (This behavior is different from <a href="qmultihash.html#replace">replace</a>(), which overwrites the value of an existing item.)</p>
<p>See also <a href="qmultihash.html#replace">replace</a>().</p>
<h3 class="fn"><a name="replace"></a><a href="qhash.html">QHash</a><Key, T>::iterator QMultiHash::replace ( const Key & <i>key</i>, const T & <i>value</i> )</h3>
<p>Inserts a new item with the key <i>key</i> and a value of <i>value</i>.</p>
<p>If there is already an item with the key <i>key</i>, that item's value is replaced with <i>value</i>.</p>
<p>If there are multiple items with the key <i>key</i>, the most recently inserted item's value is replaced with <i>value</i>.</p>
<p>See also <a href="qmultihash.html#insert">insert</a>().</p>
<h3 class="fn"><a name="operator-2b"></a>QMultiHash QMultiHash::operator+ ( const QMultiHash & <i>other</i> ) const</h3>
<p>Returns a hash that contains all the items in this hash in addition to all the items in <i>other</i>. If a key is common to both hashes, the resulting hash will contain the key multiple times.</p>
<p>See also <a href="qmultihash.html#operator-2b-eq">operator+=</a>().</p>
<h3 class="fn"><a name="operator-2b-eq"></a>QMultiHash & QMultiHash::operator+= ( const QMultiHash & <i>other</i> )</h3>
<p>Inserts all the items in the <i>other</i> hash into this hash and returns a reference to this hash.</p>
<p>See also <a href="qmultihash.html#insert">insert</a>().</p>
<p /><address><hr /><div align="center">
<table width="100%" cellspacing="0" border="0"><tr class="address">
<td width="30%">Copyright © 2006 <a href="trolltech.html">Trolltech</a></td>
<td width="40%" align="center"><a href="trademarks.html">Trademarks</a></td>
<td width="30%" align="right"><div align="right">Qt 4.2.1</div></td>
</tr></table></div></address></body>
</html>
