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<td >Qt 5.9</td><td ><a href="qtcore-index.html">Qt Core</a></td><td ><a href="qtcore-module.html">C++ Classes</a></td><td >const_iterator</td></tr></table><table class="buildversion"><tr>
<td id="buildversion" width="100%" align="right">Qt 5.9.4 Reference Documentation</td>
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<h3><a name="toc">Contents</a></h3>
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<li class="level1"><a href="#public-functions">Public Functions</a></li>
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<h1 class="title">const_iterator Class</h1>
<span class="small-subtitle">(<a href="qhash-const-iterator.html">QHash::const_iterator</a>)<br/></span>
<!-- $$$const_iterator-brief -->
<p>The <a href="qhash-const-iterator.html">QHash::const_iterator</a> class provides an STL-style const iterator for <a href="qhash.html#qhash">QHash</a> and <a href="qmultihash.html">QMultiHash</a>. <a href="#details">More...</a></p>
<!-- @@@const_iterator -->
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<tr><td class="memItemLeft rightAlign topAlign"> Header:</td><td class="memItemRight bottomAlign"> <span class="preprocessor">#include <const_iterator></span>
</td></tr><tr><td class="memItemLeft rightAlign topAlign"> qmake:</td><td class="memItemRight bottomAlign"> QT += core</td></tr></table></div><ul>
<li><a href="qhash-const-iterator-members.html">List of all members, including inherited members</a></li>
</ul>
<a name="public-functions"></a>
<h2 id="public-functions">Public Functions</h2>
<div class="table"><table class="alignedsummary">
<tr><td class="memItemLeft rightAlign topAlign"> </td><td class="memItemRight bottomAlign"><b><a href="qhash-const-iterator.html#const_iterator">const_iterator</a></b>()</td></tr>
<tr><td class="memItemLeft rightAlign topAlign"> </td><td class="memItemRight bottomAlign"><b><a href="qhash-const-iterator.html#const_iterator-2">const_iterator</a></b>(const iterator &<i>other</i>)</td></tr>
<tr><td class="memItemLeft rightAlign topAlign"> const Key &</td><td class="memItemRight bottomAlign"><b><a href="qhash-const-iterator.html#key">key</a></b>() const</td></tr>
<tr><td class="memItemLeft rightAlign topAlign"> const T &</td><td class="memItemRight bottomAlign"><b><a href="qhash-const-iterator.html#value">value</a></b>() const</td></tr>
<tr><td class="memItemLeft rightAlign topAlign"> bool </td><td class="memItemRight bottomAlign"><b><a href="qhash-const-iterator.html#operator-not-eq">operator!=</a></b>(const const_iterator &<i>other</i>) const</td></tr>
<tr><td class="memItemLeft rightAlign topAlign"> const T &</td><td class="memItemRight bottomAlign"><b><a href="qhash-const-iterator.html#operator-2a">operator*</a></b>() const</td></tr>
<tr><td class="memItemLeft rightAlign topAlign"> const_iterator </td><td class="memItemRight bottomAlign"><b><a href="qhash-const-iterator.html#operator-2b">operator+</a></b>(int <i>j</i>) const</td></tr>
<tr><td class="memItemLeft rightAlign topAlign"> const_iterator &</td><td class="memItemRight bottomAlign"><b><a href="qhash-const-iterator.html#operator-2b-2b">operator++</a></b>()</td></tr>
<tr><td class="memItemLeft rightAlign topAlign"> const_iterator </td><td class="memItemRight bottomAlign"><b><a href="qhash-const-iterator.html#operator-2b-2b-1">operator++</a></b>(<i>int</i>)</td></tr>
<tr><td class="memItemLeft rightAlign topAlign"> const_iterator &</td><td class="memItemRight bottomAlign"><b><a href="qhash-const-iterator.html#operator-2b-eq">operator+=</a></b>(int <i>j</i>)</td></tr>
<tr><td class="memItemLeft rightAlign topAlign"> const_iterator </td><td class="memItemRight bottomAlign"><b><a href="qhash-const-iterator.html#operator-">operator-</a></b>(int <i>j</i>) const</td></tr>
<tr><td class="memItemLeft rightAlign topAlign"> const_iterator &</td><td class="memItemRight bottomAlign"><b><a href="qhash-const-iterator.html#operator--">operator--</a></b>()</td></tr>
<tr><td class="memItemLeft rightAlign topAlign"> const_iterator </td><td class="memItemRight bottomAlign"><b><a href="qhash-const-iterator.html#operator---1">operator--</a></b>(<i>int</i>)</td></tr>
<tr><td class="memItemLeft rightAlign topAlign"> const_iterator &</td><td class="memItemRight bottomAlign"><b><a href="qhash-const-iterator.html#operator--eq">operator-=</a></b>(int <i>j</i>)</td></tr>
<tr><td class="memItemLeft rightAlign topAlign"> const T *</td><td class="memItemRight bottomAlign"><b><a href="qhash-const-iterator.html#operator--gt">operator-></a></b>() const</td></tr>
<tr><td class="memItemLeft rightAlign topAlign"> bool </td><td class="memItemRight bottomAlign"><b><a href="qhash-const-iterator.html#operator-eq-eq">operator==</a></b>(const const_iterator &<i>other</i>) const</td></tr>
</table></div>
<a name="details"></a>
<!-- $$$const_iterator-description -->
<div class="descr">
<h2 id="details">Detailed Description</h2>
<p>The <a href="qhash-const-iterator.html">QHash::const_iterator</a> class provides an STL-style const iterator for <a href="qhash.html#qhash">QHash</a> and <a href="qmultihash.html">QMultiHash</a>.</p>
<p><a href="qhash.html#qhash">QHash</a> features both <a href="containers.html#stl-style-iterators">STL-style iterators</a> and <a href="containers.html#java-style-iterators">Java-style iterators</a>. The STL-style iterators are more low-level and more cumbersome to use; on the other hand, they are slightly faster and, for developers who already know STL, have the advantage of familiarity.</p>
<p><a href="qhash.html#qhash">QHash</a><Key, T>::const_iterator allows you to iterate over a <a href="qhash.html#qhash">QHash</a> (or a <a href="qmultihash.html">QMultiHash</a>). If you want to modify the <a href="qhash.html#qhash">QHash</a> as you iterate over it, you must use <a href="qhash-iterator.html">QHash::iterator</a> instead. It is generally good practice to use <a href="qhash-const-iterator.html">QHash::const_iterator</a> on a non-const <a href="qhash.html#qhash">QHash</a> as well, unless you need to change the <a href="qhash.html#qhash">QHash</a> through the iterator. Const iterators are slightly faster, and can improve code readability.</p>
<p>The default <a href="qhash-const-iterator.html">QHash::const_iterator</a> constructor creates an uninitialized iterator. You must initialize it using a <a href="qhash.html#qhash">QHash</a> function like <a href="qhash.html#constBegin">QHash::constBegin</a>(), <a href="qhash.html#constEnd">QHash::constEnd</a>(), or <a href="qhash.html#find">QHash::find</a>() before you can start iterating. Here's a typical loop that prints all the (key, value) pairs stored in a hash:</p>
<pre class="cpp">
<span class="type"><a href="qhash.html#QHash">QHash</a></span><span class="operator"><</span><span class="type"><a href="qstring.html">QString</a></span><span class="operator">,</span> <span class="type">int</span><span class="operator">></span> hash;
hash<span class="operator">.</span>insert(<span class="string">"January"</span><span class="operator">,</span> <span class="number">1</span>);
hash<span class="operator">.</span>insert(<span class="string">"February"</span><span class="operator">,</span> <span class="number">2</span>);
<span class="operator">.</span><span class="operator">.</span><span class="operator">.</span>
hash<span class="operator">.</span>insert(<span class="string">"December"</span><span class="operator">,</span> <span class="number">12</span>);
<span class="type"><a href="qhash.html#QHash">QHash</a></span><span class="operator"><</span><span class="type"><a href="qstring.html">QString</a></span><span class="operator">,</span> <span class="type">int</span><span class="operator">></span><span class="operator">::</span>const_iterator i;
<span class="keyword">for</span> (i <span class="operator">=</span> hash<span class="operator">.</span>constBegin(); i <span class="operator">!</span><span class="operator">=</span> hash<span class="operator">.</span>constEnd(); <span class="operator">+</span><span class="operator">+</span>i)
cout <span class="operator"><</span><span class="operator"><</span> i<span class="operator">.</span>key() <span class="operator"><</span><span class="operator"><</span> <span class="string">": "</span> <span class="operator"><</span><span class="operator"><</span> i<span class="operator">.</span>value() <span class="operator"><</span><span class="operator"><</span> endl;
</pre>
<p>Unlike <a href="qmap.html">QMap</a>, which orders its items by key, <a href="qhash.html#qhash">QHash</a> stores its items in an arbitrary order. The only guarantee is that items that share the same key (because they were inserted using <a href="qhash.html#insertMulti">QHash::insertMulti</a>()) will appear consecutively, from the most recently to the least recently inserted value.</p>
<p>Multiple iterators can be used on the same hash. However, be aware that any modification performed directly on the <a href="qhash.html#qhash">QHash</a> has the potential of dramatically changing the order in which the items are stored in the hash, as they might cause <a href="qhash.html#qhash">QHash</a> to rehash its internal data structure. If you need to keep iterators over a long period of time, we recommend that you use <a href="qmap.html">QMap</a> rather than <a href="qhash.html#qhash">QHash</a>.</p>
<p><b>Warning:</b> Iterators on implicitly shared containers do not work exactly like STL-iterators. You should avoid copying a container while iterators are active on that container. For more information, read <a href="containers.html#implicit-sharing-iterator-problem">Implicit sharing iterator problem</a>.</p>
</div>
<p><b>See also </b><a href="qhash-iterator.html">QHash::iterator</a> and <a href="qhashiterator.html">QHashIterator</a>.</p>
<!-- @@@const_iterator -->
<div class="func">
<h2>Member Function Documentation</h2>
<!-- $$$const_iterator[overload1]$$$const_iterator -->
<h3 class="fn" id="const_iterator"><a name="const_iterator"></a>const_iterator::<span class="name">const_iterator</span>()</h3>
<p>Constructs an uninitialized iterator.</p>
<p>Functions like <a href="qhash-const-iterator.html#key">key</a>(), <a href="qhash-const-iterator.html#value">value</a>(), and operator++() must not be called on an uninitialized iterator. Use operator=() to assign a value to it before using it.</p>
<p><b>See also </b><a href="qhash.html#constBegin">QHash::constBegin</a>() and <a href="qhash.html#constEnd">QHash::constEnd</a>().</p>
<!-- @@@const_iterator -->
<!-- $$$const_iterator$$$const_iteratorconstiterator& -->
<h3 class="fn" id="const_iterator-2"><a name="const_iterator-2"></a>const_iterator::<span class="name">const_iterator</span>(const <span class="type"><a href="qhash-iterator.html">iterator</a></span> &<i>other</i>)</h3>
<p>Constructs a copy of <i>other</i>.</p>
<!-- @@@const_iterator -->
<!-- $$$key[overload1]$$$key -->
<h3 class="fn" id="key"><a name="key"></a>const <span class="type">Key</span> &const_iterator::<span class="name">key</span>() const</h3>
<p>Returns the current item's key.</p>
<p><b>See also </b><a href="qhash-const-iterator.html#value">value</a>().</p>
<!-- @@@key -->
<!-- $$$value[overload1]$$$value -->
<h3 class="fn" id="value"><a name="value"></a>const <span class="type">T</span> &const_iterator::<span class="name">value</span>() const</h3>
<p>Returns the current item's value.</p>
<p><b>See also </b><a href="qhash-const-iterator.html#key">key</a>() and <a href="qhash-const-iterator.html#operator-2a">operator*</a>().</p>
<!-- @@@value -->
<!-- $$$operator!=[overload1]$$$operator!=constconst_iterator& -->
<h3 class="fn" id="operator-not-eq"><a name="operator-not-eq"></a><span class="type">bool</span> const_iterator::<span class="name">operator!=</span>(const <span class="type"><a href="qhash-const-iterator.html#const_iterator">const_iterator</a></span> &<i>other</i>) const</h3>
<p>Returns <code>true</code> if <i>other</i> points to a different item than this iterator; otherwise returns <code>false</code>.</p>
<p><b>See also </b><a href="qhash-const-iterator.html#operator-eq-eq">operator==</a>().</p>
<!-- @@@operator!= -->
<!-- $$$operator*[overload1]$$$operator* -->
<h3 class="fn" id="operator-2a"><a name="operator-2a"></a>const <span class="type">T</span> &const_iterator::<span class="name">operator*</span>() const</h3>
<p>Returns the current item's value.</p>
<p>Same as <a href="qhash-const-iterator.html#value">value</a>().</p>
<p><b>See also </b><a href="qhash-const-iterator.html#key">key</a>().</p>
<!-- @@@operator* -->
<!-- $$$operator+[overload1]$$$operator+int -->
<h3 class="fn" id="operator-2b"><a name="operator-2b"></a><span class="type"><a href="qhash-const-iterator.html#const_iterator">const_iterator</a></span> const_iterator::<span class="name">operator+</span>(<span class="type">int</span> <i>j</i>) const</h3>
<p>Returns an iterator to the item at <i>j</i> positions forward from this iterator. (If <i>j</i> is negative, the iterator goes backward.)</p>
<p>This operation can be slow for large <i>j</i> values.</p>
<p><b>See also </b><a href="qhash-const-iterator.html#operator-">operator-</a>().</p>
<!-- @@@operator+ -->
<!-- $$$operator++[overload1]$$$operator++ -->
<h3 class="fn" id="operator-2b-2b"><a name="operator-2b-2b"></a><span class="type"><a href="qhash-const-iterator.html#const_iterator">const_iterator</a></span> &const_iterator::<span class="name">operator++</span>()</h3>
<p>The prefix ++ operator (<code>++i</code>) advances the iterator to the next item in the hash and returns an iterator to the new current item.</p>
<p>Calling this function on <a href="qhash.html#end">QHash::end</a>() leads to undefined results.</p>
<p><b>See also </b><a href="qhash-const-iterator.html#operator--">operator--</a>().</p>
<!-- @@@operator++ -->
<!-- $$$operator++$$$operator++int -->
<h3 class="fn" id="operator-2b-2b-1"><a name="operator-2b-2b-1"></a><span class="type"><a href="qhash-const-iterator.html#const_iterator">const_iterator</a></span> const_iterator::<span class="name">operator++</span>(<i>int</i>)</h3>
<p>This is an overloaded function.</p>
<p>The postfix ++ operator (<code>i++</code>) advances the iterator to the next item in the hash and returns an iterator to the previously current item.</p>
<!-- @@@operator++ -->
<!-- $$$operator+=[overload1]$$$operator+=int -->
<h3 class="fn" id="operator-2b-eq"><a name="operator-2b-eq"></a><span class="type"><a href="qhash-const-iterator.html#const_iterator">const_iterator</a></span> &const_iterator::<span class="name">operator+=</span>(<span class="type">int</span> <i>j</i>)</h3>
<p>Advances the iterator by <i>j</i> items. (If <i>j</i> is negative, the iterator goes backward.)</p>
<p>This operation can be slow for large <i>j</i> values.</p>
<p><b>See also </b><a href="qhash-const-iterator.html#operator--eq">operator-=</a>() and <a href="qhash-const-iterator.html#operator-2b">operator+</a>().</p>
<!-- @@@operator+= -->
<!-- $$$operator-[overload1]$$$operator-int -->
<h3 class="fn" id="operator-"><a name="operator-"></a><span class="type"><a href="qhash-const-iterator.html#const_iterator">const_iterator</a></span> const_iterator::<span class="name">operator-</span>(<span class="type">int</span> <i>j</i>) const</h3>
<p>Returns an iterator to the item at <i>j</i> positions backward from this iterator. (If <i>j</i> is negative, the iterator goes forward.)</p>
<p>This operation can be slow for large <i>j</i> values.</p>
<p><b>See also </b><a href="qhash-const-iterator.html#operator-2b">operator+</a>().</p>
<!-- @@@operator- -->
<!-- $$$operator--[overload1]$$$operator-- -->
<h3 class="fn" id="operator--"><a name="operator--"></a><span class="type"><a href="qhash-const-iterator.html#const_iterator">const_iterator</a></span> &const_iterator::<span class="name">operator--</span>()</h3>
<p>The prefix -- operator (<code>--i</code>) makes the preceding item current and returns an iterator pointing to the new current item.</p>
<p>Calling this function on <a href="qhash.html#begin">QHash::begin</a>() leads to undefined results.</p>
<p><b>See also </b><a href="qhash-const-iterator.html#operator-2b-2b">operator++</a>().</p>
<!-- @@@operator-- -->
<!-- $$$operator--$$$operator--int -->
<h3 class="fn" id="operator---1"><a name="operator---1"></a><span class="type"><a href="qhash-const-iterator.html#const_iterator">const_iterator</a></span> const_iterator::<span class="name">operator--</span>(<i>int</i>)</h3>
<p>This is an overloaded function.</p>
<p>The postfix -- operator (<code>i--</code>) makes the preceding item current and returns an iterator pointing to the previously current item.</p>
<!-- @@@operator-- -->
<!-- $$$operator-=[overload1]$$$operator-=int -->
<h3 class="fn" id="operator--eq"><a name="operator--eq"></a><span class="type"><a href="qhash-const-iterator.html#const_iterator">const_iterator</a></span> &const_iterator::<span class="name">operator-=</span>(<span class="type">int</span> <i>j</i>)</h3>
<p>Makes the iterator go back by <i>j</i> items. (If <i>j</i> is negative, the iterator goes forward.)</p>
<p>This operation can be slow for large <i>j</i> values.</p>
<p><b>See also </b><a href="qhash-const-iterator.html#operator-2b-eq">operator+=</a>() and <a href="qhash-const-iterator.html#operator-">operator-</a>().</p>
<!-- @@@operator-= -->
<!-- $$$operator->[overload1]$$$operator-> -->
<h3 class="fn" id="operator--gt"><a name="operator--gt"></a>const <span class="type">T</span> *const_iterator::<span class="name">operator-></span>() const</h3>
<p>Returns a pointer to the current item's value.</p>
<p><b>See also </b><a href="qhash-const-iterator.html#value">value</a>().</p>
<!-- @@@operator-> -->
<!-- $$$operator==[overload1]$$$operator==constconst_iterator& -->
<h3 class="fn" id="operator-eq-eq"><a name="operator-eq-eq"></a><span class="type">bool</span> const_iterator::<span class="name">operator==</span>(const <span class="type"><a href="qhash-const-iterator.html#const_iterator">const_iterator</a></span> &<i>other</i>) const</h3>
<p>Returns <code>true</code> if <i>other</i> points to the same item as this iterator; otherwise returns <code>false</code>.</p>
<p><b>See also </b><a href="qhash-const-iterator.html#operator-not-eq">operator!=</a>().</p>
<!-- @@@operator== -->
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