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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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<li class="level1"><a href="#public-types">Public Types</a></li>
<li class="level1"><a href="#public-functions">Public Functions</a></li>
<li class="level1"><a href="#details">Detailed Description</a></li>
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<h1 class="title">const_iterator Class</h1>
<span class="small-subtitle">(<a href="qmap-const-iterator.html">QMap::const_iterator</a>)<br/></span>
<!-- $$$const_iterator-brief -->
<p>The <a href="qmap-const-iterator.html">QMap::const_iterator</a> class provides an STL-style const iterator for <a href="qmap.html">QMap</a> and <a href="qmultimap.html">QMultiMap</a>. <a href="#details">More...</a></p>
<!-- @@@const_iterator -->
<div class="table"><table class="alignedsummary">
<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="qmap-const-iterator-members.html">List of all members, including inherited members</a></li>
</ul>
<a name="public-types"></a>
<h2 id="public-types">Public Types</h2>
<div class="table"><table class="alignedsummary">
<tr><td class="memItemLeft rightAlign topAlign"> typedef </td><td class="memItemRight bottomAlign"><b><a href="qmap-const-iterator.html#iterator_category-typedef">iterator_category</a></b></td></tr>
</table></div>
<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="qmap-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="qmap-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="qmap-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="qmap-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="qmap-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="qmap-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="qmap-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="qmap-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="qmap-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="qmap-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="qmap-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="qmap-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="qmap-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="qmap-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="qmap-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="qmap-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="qmap-const-iterator.html">QMap::const_iterator</a> class provides an STL-style const iterator for <a href="qmap.html">QMap</a> and <a href="qmultimap.html">QMultiMap</a>.</p>
<p><a href="qmap.html">QMap</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="qmap.html">QMap</a><Key, T>::const_iterator allows you to iterate over a <a href="qmap.html">QMap</a> (or a <a href="qmultimap.html">QMultiMap</a>). If you want to modify the <a href="qmap.html">QMap</a> as you iterate over it, you must use <a href="qmap-iterator.html">QMap::iterator</a> instead. It is generally good practice to use <a href="qmap-const-iterator.html">QMap::const_iterator</a> on a non-const <a href="qmap.html">QMap</a> as well, unless you need to change the <a href="qmap.html">QMap</a> through the iterator. Const iterators are slightly faster, and can improve code readability.</p>
<p>The default <a href="qmap-const-iterator.html">QMap::const_iterator</a> constructor creates an uninitialized iterator. You must initialize it using a <a href="qmap.html">QMap</a> function like <a href="qmap.html#constBegin">QMap::constBegin</a>(), <a href="qmap.html#constEnd">QMap::constEnd</a>(), or <a href="qmap.html#find">QMap::find</a>() before you can start iterating. Here's a typical loop that prints all the (key, value) pairs stored in a map:</p>
<pre class="cpp">
<span class="type"><a href="qmap.html#QMap">QMap</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> map;
map<span class="operator">.</span>insert(<span class="string">"January"</span><span class="operator">,</span> <span class="number">1</span>);
map<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>
map<span class="operator">.</span>insert(<span class="string">"December"</span><span class="operator">,</span> <span class="number">12</span>);
<span class="type"><a href="qmap.html#QMap">QMap</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> map<span class="operator">.</span>constBegin(); i <span class="operator">!</span><span class="operator">=</span> map<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="qhash.html#qhash">QHash</a>, which stores its items in an arbitrary order, <a href="qmap.html">QMap</a> stores its items ordered by key. Items that share the same key (because they were inserted using <a href="qmap.html#insertMulti">QMap::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 map. If you add items to the map, existing iterators will remain valid. If you remove items from the map, iterators that point to the removed items will become dangling iterators.</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="qmap-iterator.html">QMap::iterator</a>, <a href="qmap-key-iterator.html">QMap::key_iterator</a>, and <a href="qmapiterator.html">QMapIterator</a>.</p>
<!-- @@@const_iterator -->
<div class="types">
<h2>Member Type Documentation</h2>
<!-- $$$iterator_category -->
<h3 class="fn" id="iterator_category-typedef"><a name="iterator_category-typedef"></a>typedef const_iterator::<span class="name">iterator_category</span></h3>
<p>A synonym for <i>std::bidirectional_iterator_tag</i> indicating this iterator is a bidirectional iterator.</p>
<!-- @@@iterator_category -->
</div>
<div class="func">
<h2>Member Function Documentation</h2>
<!-- $$$const_iterator[overload1]$$$const_iterator -->
<h3 class="fn" id="const_iterator"><a name="const_iterator"></a>const_iterator::<span class="name">const_iterator</span>()</h3>
<p>Constructs an uninitialized iterator.</p>
<p>Functions like <a href="qmap-const-iterator.html#key">key</a>(), <a href="qmap-const-iterator.html#value">value</a>(), and operator++() must not be called on an uninitialized iterator. Use operator=() to assign a value to it before using it.</p>
<p><b>See also </b><a href="qmap.html#constBegin">QMap::constBegin</a>() and <a href="qmap.html#constEnd">QMap::constEnd</a>().</p>
<!-- @@@const_iterator -->
<!-- $$$const_iterator$$$const_iteratorconstiterator& -->
<h3 class="fn" id="const_iterator-2"><a name="const_iterator-2"></a>const_iterator::<span class="name">const_iterator</span>(const <span class="type"><a href="qmap-iterator.html">iterator</a></span> &<i>other</i>)</h3>
<p>Constructs a copy of <i>other</i>.</p>
<!-- @@@const_iterator -->
<!-- $$$key[overload1]$$$key -->
<h3 class="fn" id="key"><a name="key"></a>const <span class="type">Key</span> &const_iterator::<span class="name">key</span>() const</h3>
<p>Returns the current item's key.</p>
<p><b>See also </b><a href="qmap-const-iterator.html#value">value</a>().</p>
<!-- @@@key -->
<!-- $$$value[overload1]$$$value -->
<h3 class="fn" id="value"><a name="value"></a>const <span class="type">T</span> &const_iterator::<span class="name">value</span>() const</h3>
<p>Returns the current item's value.</p>
<p><b>See also </b><a href="qmap-const-iterator.html#key">key</a>() and <a href="qmap-const-iterator.html#operator-2a">operator*</a>().</p>
<!-- @@@value -->
<!-- $$$operator!=[overload1]$$$operator!=constconst_iterator& -->
<h3 class="fn" id="operator-not-eq"><a name="operator-not-eq"></a><span class="type">bool</span> const_iterator::<span class="name">operator!=</span>(const <span class="type"><a href="qmap-const-iterator.html#const_iterator">const_iterator</a></span> &<i>other</i>) const</h3>
<p>Returns <code>true</code> if <i>other</i> points to a different item than this iterator; otherwise returns <code>false</code>.</p>
<p><b>See also </b><a href="qmap-const-iterator.html#operator-eq-eq">operator==</a>().</p>
<!-- @@@operator!= -->
<!-- $$$operator*[overload1]$$$operator* -->
<h3 class="fn" id="operator-2a"><a name="operator-2a"></a>const <span class="type">T</span> &const_iterator::<span class="name">operator*</span>() const</h3>
<p>Returns the current item's value.</p>
<p>Same as <a href="qmap-const-iterator.html#value">value</a>().</p>
<p><b>See also </b><a href="qmap-const-iterator.html#key">key</a>().</p>
<!-- @@@operator* -->
<!-- $$$operator+[overload1]$$$operator+int -->
<h3 class="fn" id="operator-2b"><a name="operator-2b"></a><span class="type"><a href="qmap-const-iterator.html#const_iterator">const_iterator</a></span> const_iterator::<span class="name">operator+</span>(<span class="type">int</span> <i>j</i>) const</h3>
<p>Returns an iterator to the item at <i>j</i> positions forward from this iterator. (If <i>j</i> is negative, the iterator goes backward.)</p>
<p>This operation can be slow for large <i>j</i> values.</p>
<p><b>See also </b><a href="qmap-const-iterator.html#operator-">operator-</a>().</p>
<!-- @@@operator+ -->
<!-- $$$operator++[overload1]$$$operator++ -->
<h3 class="fn" id="operator-2b-2b"><a name="operator-2b-2b"></a><span class="type"><a href="qmap-const-iterator.html#const_iterator">const_iterator</a></span> &const_iterator::<span class="name">operator++</span>()</h3>
<p>The prefix ++ operator (<code>++i</code>) advances the iterator to the next item in the map and returns an iterator to the new current item.</p>
<p>Calling this function on <a href="qmap.html#end">QMap::end</a>() leads to undefined results.</p>
<p><b>See also </b><a href="qmap-const-iterator.html#operator--">operator--</a>().</p>
<!-- @@@operator++ -->
<!-- $$$operator++$$$operator++int -->
<h3 class="fn" id="operator-2b-2b-1"><a name="operator-2b-2b-1"></a><span class="type"><a href="qmap-const-iterator.html#const_iterator">const_iterator</a></span> const_iterator::<span class="name">operator++</span>(<i>int</i>)</h3>
<p>This is an overloaded function.</p>
<p>The postfix ++ operator (<code>i++</code>) advances the iterator to the next item in the map and returns an iterator to the previously current item.</p>
<!-- @@@operator++ -->
<!-- $$$operator+=[overload1]$$$operator+=int -->
<h3 class="fn" id="operator-2b-eq"><a name="operator-2b-eq"></a><span class="type"><a href="qmap-const-iterator.html#const_iterator">const_iterator</a></span> &const_iterator::<span class="name">operator+=</span>(<span class="type">int</span> <i>j</i>)</h3>
<p>Advances the iterator by <i>j</i> items. (If <i>j</i> is negative, the iterator goes backward.)</p>
<p>This operation can be slow for large <i>j</i> values.</p>
<p><b>See also </b><a href="qmap-const-iterator.html#operator--eq">operator-=</a>() and <a href="qmap-const-iterator.html#operator-2b">operator+</a>().</p>
<!-- @@@operator+= -->
<!-- $$$operator-[overload1]$$$operator-int -->
<h3 class="fn" id="operator-"><a name="operator-"></a><span class="type"><a href="qmap-const-iterator.html#const_iterator">const_iterator</a></span> const_iterator::<span class="name">operator-</span>(<span class="type">int</span> <i>j</i>) const</h3>
<p>Returns an iterator to the item at <i>j</i> positions backward from this iterator. (If <i>j</i> is negative, the iterator goes forward.)</p>
<p>This operation can be slow for large <i>j</i> values.</p>
<p><b>See also </b><a href="qmap-const-iterator.html#operator-2b">operator+</a>().</p>
<!-- @@@operator- -->
<!-- $$$operator--[overload1]$$$operator-- -->
<h3 class="fn" id="operator--"><a name="operator--"></a><span class="type"><a href="qmap-const-iterator.html#const_iterator">const_iterator</a></span> &const_iterator::<span class="name">operator--</span>()</h3>
<p>The prefix -- operator (<code>--i</code>) makes the preceding item current and returns an iterator pointing to the new current item.</p>
<p>Calling this function on <a href="qmap.html#begin">QMap::begin</a>() leads to undefined results.</p>
<p><b>See also </b><a href="qmap-const-iterator.html#operator-2b-2b">operator++</a>().</p>
<!-- @@@operator-- -->
<!-- $$$operator--$$$operator--int -->
<h3 class="fn" id="operator---1"><a name="operator---1"></a><span class="type"><a href="qmap-const-iterator.html#const_iterator">const_iterator</a></span> const_iterator::<span class="name">operator--</span>(<i>int</i>)</h3>
<p>This is an overloaded function.</p>
<p>The postfix -- operator (<code>i--</code>) makes the preceding item current and returns an iterator pointing to the previously current item.</p>
<!-- @@@operator-- -->
<!-- $$$operator-=[overload1]$$$operator-=int -->
<h3 class="fn" id="operator--eq"><a name="operator--eq"></a><span class="type"><a href="qmap-const-iterator.html#const_iterator">const_iterator</a></span> &const_iterator::<span class="name">operator-=</span>(<span class="type">int</span> <i>j</i>)</h3>
<p>Makes the iterator go back by <i>j</i> items. (If <i>j</i> is negative, the iterator goes forward.)</p>
<p>This operation can be slow for large <i>j</i> values.</p>
<p><b>See also </b><a href="qmap-const-iterator.html#operator-2b-eq">operator+=</a>() and <a href="qmap-const-iterator.html#operator-">operator-</a>().</p>
<!-- @@@operator-= -->
<!-- $$$operator->[overload1]$$$operator-> -->
<h3 class="fn" id="operator--gt"><a name="operator--gt"></a>const <span class="type">T</span> *const_iterator::<span class="name">operator-></span>() const</h3>
<p>Returns a pointer to the current item's value.</p>
<p><b>See also </b><a href="qmap-const-iterator.html#value">value</a>().</p>
<!-- @@@operator-> -->
<!-- $$$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="qmap-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="qmap-const-iterator.html#operator-not-eq">operator!=</a>().</p>
<!-- @@@operator== -->
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