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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 >QMapIterator</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>
<li class="level1"><a href="#details">Detailed Description</a></li>
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<h1 class="title">QMapIterator Class</h1>
<!-- $$$QMapIterator-brief -->
<p>The <a href="qmapiterator.html">QMapIterator</a> class provides a Java-style const iterator for <a href="qmap.html">QMap</a> and <a href="qmultimap.html">QMultiMap</a>. <a href="#details">More...</a></p>
<!-- @@@QMapIterator -->
<div class="table"><table class="alignedsummary">
<tr><td class="memItemLeft rightAlign topAlign"> Header:</td><td class="memItemRight bottomAlign"> <span class="preprocessor">#include <QMapIterator></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="qmapiterator-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="qmapiterator.html#QMapIterator">QMapIterator</a></b>(const QMap<Key, T> &<i>map</i>)</td></tr>
<tr><td class="memItemLeft rightAlign topAlign"> bool </td><td class="memItemRight bottomAlign"><b><a href="qmapiterator.html#findNext">findNext</a></b>(const T &<i>value</i>)</td></tr>
<tr><td class="memItemLeft rightAlign topAlign"> bool </td><td class="memItemRight bottomAlign"><b><a href="qmapiterator.html#findPrevious">findPrevious</a></b>(const T &<i>value</i>)</td></tr>
<tr><td class="memItemLeft rightAlign topAlign"> bool </td><td class="memItemRight bottomAlign"><b><a href="qmapiterator.html#hasNext">hasNext</a></b>() const</td></tr>
<tr><td class="memItemLeft rightAlign topAlign"> bool </td><td class="memItemRight bottomAlign"><b><a href="qmapiterator.html#hasPrevious">hasPrevious</a></b>() const</td></tr>
<tr><td class="memItemLeft rightAlign topAlign"> const Key &</td><td class="memItemRight bottomAlign"><b><a href="qmapiterator.html#key">key</a></b>() const</td></tr>
<tr><td class="memItemLeft rightAlign topAlign"> Item </td><td class="memItemRight bottomAlign"><b><a href="qmapiterator.html#next">next</a></b>()</td></tr>
<tr><td class="memItemLeft rightAlign topAlign"> Item </td><td class="memItemRight bottomAlign"><b><a href="qmapiterator.html#peekNext">peekNext</a></b>() const</td></tr>
<tr><td class="memItemLeft rightAlign topAlign"> Item </td><td class="memItemRight bottomAlign"><b><a href="qmapiterator.html#peekPrevious">peekPrevious</a></b>() const</td></tr>
<tr><td class="memItemLeft rightAlign topAlign"> Item </td><td class="memItemRight bottomAlign"><b><a href="qmapiterator.html#previous">previous</a></b>()</td></tr>
<tr><td class="memItemLeft rightAlign topAlign"> void </td><td class="memItemRight bottomAlign"><b><a href="qmapiterator.html#toBack">toBack</a></b>()</td></tr>
<tr><td class="memItemLeft rightAlign topAlign"> void </td><td class="memItemRight bottomAlign"><b><a href="qmapiterator.html#toFront">toFront</a></b>()</td></tr>
<tr><td class="memItemLeft rightAlign topAlign"> const T &</td><td class="memItemRight bottomAlign"><b><a href="qmapiterator.html#value">value</a></b>() const</td></tr>
<tr><td class="memItemLeft rightAlign topAlign"> QMapIterator &</td><td class="memItemRight bottomAlign"><b><a href="qmapiterator.html#operator-eq">operator=</a></b>(const QMap<Key, T> &<i>map</i>)</td></tr>
</table></div>
<a name="details"></a>
<!-- $$$QMapIterator-description -->
<div class="descr">
<h2 id="details">Detailed Description</h2>
<p>The <a href="qmapiterator.html">QMapIterator</a> class provides a Java-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> has both <a href="containers.html#java-style-iterators">Java-style iterators</a> and <a href="containers.html#stl-style-iterators">STL-style iterators</a>. The Java-style iterators are more high-level and easier to use than the STL-style iterators; on the other hand, they are slightly less efficient.</p>
<p><a href="qmapiterator.html">QMapIterator</a><Key, T> 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 map as you iterate over it, use <a href="qmutablemapiterator.html">QMutableMapIterator</a> instead.</p>
<p>The <a href="qmapiterator.html">QMapIterator</a> constructor takes a <a href="qmap.html">QMap</a> as argument. After construction, the iterator is located at the very beginning of the map (before the first item). Here's how to iterate over all the elements sequentially:</p>
<pre class="cpp">
<span class="type"><a href="qmap.html">QMap</a></span><span class="operator"><</span><span class="type">int</span><span class="operator">,</span> <span class="type"><a href="../qtwidgets/qwidget.html">QWidget</a></span> <span class="operator">*</span><span class="operator">></span> map;
<span class="operator">.</span><span class="operator">.</span><span class="operator">.</span>
<span class="type"><a href="qmapiterator.html#QMapIterator">QMapIterator</a></span><span class="operator"><</span><span class="type">int</span><span class="operator">,</span> <span class="type"><a href="../qtwidgets/qwidget.html">QWidget</a></span> <span class="operator">*</span><span class="operator">></span> i(map);
<span class="keyword">while</span> (i<span class="operator">.</span>hasNext()) {
i<span class="operator">.</span>next();
<a href="qtglobal.html#qDebug">qDebug</a>() <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();
}
</pre>
<p>The <a href="qmapiterator.html#next">next</a>() function returns the next item in the map and advances the iterator. The <a href="qmapiterator.html#key">key</a>() and <a href="qmapiterator.html#value">value</a>() functions return the key and value of the last item that was jumped over.</p>
<p>Unlike STL-style iterators, Java-style iterators point <i>between</i> items rather than directly <i>at</i> items. The first call to <a href="qmapiterator.html#next">next</a>() advances the iterator to the position between the first and second item, and returns the first item; the second call to <a href="qmapiterator.html#next">next</a>() advances the iterator to the position between the second and third item; and so on.</p>
<p class="centerAlign"><img src="images/javaiterators1.png" alt="" /></p><p>Here's how to iterate over the elements in reverse order:</p>
<pre class="cpp">
<span class="type"><a href="qmapiterator.html#QMapIterator">QMapIterator</a></span><span class="operator"><</span><span class="type">int</span><span class="operator">,</span> <span class="type"><a href="../qtwidgets/qwidget.html">QWidget</a></span> <span class="operator">*</span><span class="operator">></span> i(map);
i<span class="operator">.</span>toBack();
<span class="keyword">while</span> (i<span class="operator">.</span>hasPrevious()) {
i<span class="operator">.</span>previous();
<a href="qtglobal.html#qDebug">qDebug</a>() <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();
}
</pre>
<p>If you want to find all occurrences of a particular value, use <a href="qmapiterator.html#findNext">findNext</a>() or <a href="qmapiterator.html#findPrevious">findPrevious</a>() in a loop. For example:</p>
<pre class="cpp">
<span class="type"><a href="qmapiterator.html#QMapIterator">QMapIterator</a></span><span class="operator"><</span><span class="type">int</span><span class="operator">,</span> <span class="type"><a href="../qtwidgets/qwidget.html">QWidget</a></span> <span class="operator">*</span><span class="operator">></span> i(map);
<span class="keyword">while</span> (i<span class="operator">.</span>findNext(widget)) {
<a href="qtglobal.html#qDebug">qDebug</a>() <span class="operator"><</span><span class="operator"><</span> <span class="string">"Found widget "</span> <span class="operator"><</span><span class="operator"><</span> widget <span class="operator"><</span><span class="operator"><</span> <span class="string">" under key "</span>
<span class="operator"><</span><span class="operator"><</span> i<span class="operator">.</span>key();
}
</pre>
<p>Multiple iterators can be used on the same map. If the map is modified while a <a href="qmapiterator.html">QMapIterator</a> is active, the <a href="qmapiterator.html">QMapIterator</a> will continue iterating over the original map, ignoring the modified copy.</p>
</div>
<p><b>See also </b><a href="qmutablemapiterator.html">QMutableMapIterator</a> and <a href="qmap-const-iterator.html">QMap::const_iterator</a>.</p>
<!-- @@@QMapIterator -->
<div class="func">
<h2>Member Function Documentation</h2>
<!-- $$$QMapIterator[overload1]$$$QMapIteratorconstQMap<Key,T>& -->
<h3 class="fn" id="QMapIterator"><a name="QMapIterator"></a>QMapIterator::<span class="name">QMapIterator</span>(const <span class="type"><a href="qmap.html">QMap</a></span><<span class="type">Key</span>, <span class="type">T</span>> &<i>map</i>)</h3>
<p>Constructs an iterator for traversing <i>map</i>. The iterator is set to be at the front of the map (before the first item).</p>
<p><b>See also </b><a href="qmapiterator.html#operator-eq">operator=</a>().</p>
<!-- @@@QMapIterator -->
<!-- $$$findNext[overload1]$$$findNextconstT& -->
<h3 class="fn" id="findNext"><a name="findNext"></a><span class="type">bool</span> QMapIterator::<span class="name">findNext</span>(const <span class="type">T</span> &<i>value</i>)</h3>
<p>Searches for <i>value</i> starting from the current iterator position forward. Returns <code>true</code> if a (key, value) pair with value <i>value</i> is found; otherwise returns <code>false</code>.</p>
<p>After the call, if <i>value</i> was found, the iterator is positioned just after the matching item; otherwise, the iterator is positioned at the back of the container.</p>
<p><b>See also </b><a href="qmapiterator.html#findPrevious">findPrevious</a>().</p>
<!-- @@@findNext -->
<!-- $$$findPrevious[overload1]$$$findPreviousconstT& -->
<h3 class="fn" id="findPrevious"><a name="findPrevious"></a><span class="type">bool</span> QMapIterator::<span class="name">findPrevious</span>(const <span class="type">T</span> &<i>value</i>)</h3>
<p>Searches for <i>value</i> starting from the current iterator position backward. Returns <code>true</code> if a (key, value) pair with value <i>value</i> is found; otherwise returns <code>false</code>.</p>
<p>After the call, if <i>value</i> was found, the iterator is positioned just before the matching item; otherwise, the iterator is positioned at the front of the container.</p>
<p><b>See also </b><a href="qmapiterator.html#findNext">findNext</a>().</p>
<!-- @@@findPrevious -->
<!-- $$$hasNext[overload1]$$$hasNext -->
<h3 class="fn" id="hasNext"><a name="hasNext"></a><span class="type">bool</span> QMapIterator::<span class="name">hasNext</span>() const</h3>
<p>Returns <code>true</code> if there is at least one item ahead of the iterator, i.e. the iterator is <i>not</i> at the back of the container; otherwise returns <code>false</code>.</p>
<p><b>See also </b><a href="qmapiterator.html#hasPrevious">hasPrevious</a>() and <a href="qmapiterator.html#next">next</a>().</p>
<!-- @@@hasNext -->
<!-- $$$hasPrevious[overload1]$$$hasPrevious -->
<h3 class="fn" id="hasPrevious"><a name="hasPrevious"></a><span class="type">bool</span> QMapIterator::<span class="name">hasPrevious</span>() const</h3>
<p>Returns <code>true</code> if there is at least one item behind the iterator, i.e. the iterator is <i>not</i> at the front of the container; otherwise returns <code>false</code>.</p>
<p><b>See also </b><a href="qmapiterator.html#hasNext">hasNext</a>() and <a href="qmapiterator.html#previous">previous</a>().</p>
<!-- @@@hasPrevious -->
<!-- $$$key[overload1]$$$key -->
<h3 class="fn" id="key"><a name="key"></a>const <span class="type">Key</span> &QMapIterator::<span class="name">key</span>() const</h3>
<p>Returns the key of the last item that was jumped over using one of the traversal functions (<a href="qmapiterator.html#next">next</a>(), <a href="qmapiterator.html#previous">previous</a>(), <a href="qmapiterator.html#findNext">findNext</a>(), <a href="qmapiterator.html#findPrevious">findPrevious</a>()).</p>
<p>After a call to <a href="qmapiterator.html#next">next</a>() or <a href="qmapiterator.html#findNext">findNext</a>(), key() is equivalent to <a href="qmapiterator.html#peekPrevious">peekPrevious</a>().key(). After a call to <a href="qmapiterator.html#previous">previous</a>() or <a href="qmapiterator.html#findPrevious">findPrevious</a>(), key() is equivalent to <a href="qmapiterator.html#peekNext">peekNext</a>().key().</p>
<p><b>See also </b><a href="qmapiterator.html#value">value</a>().</p>
<!-- @@@key -->
<!-- $$$next[overload1]$$$next -->
<h3 class="fn" id="next"><a name="next"></a><span class="type">Item</span> QMapIterator::<span class="name">next</span>()</h3>
<p>Returns the next item and advances the iterator by one position.</p>
<p>Call <a href="qmapiterator.html#key">key</a>() on the return value to obtain the item's key, and <a href="qmapiterator.html#value">value</a>() to obtain the value.</p>
<p>Calling this function on an iterator located at the back of the container leads to undefined results.</p>
<p><b>See also </b><a href="qmapiterator.html#hasNext">hasNext</a>(), <a href="qmapiterator.html#peekNext">peekNext</a>(), and <a href="qmapiterator.html#previous">previous</a>().</p>
<!-- @@@next -->
<!-- $$$peekNext[overload1]$$$peekNext -->
<h3 class="fn" id="peekNext"><a name="peekNext"></a><span class="type">Item</span> QMapIterator::<span class="name">peekNext</span>() const</h3>
<p>Returns the next item without moving the iterator.</p>
<p>Call <a href="qmapiterator.html#key">key</a>() on the return value to obtain the item's key, and <a href="qmapiterator.html#value">value</a>() to obtain the value.</p>
<p>Calling this function on an iterator located at the back of the container leads to undefined results.</p>
<p><b>See also </b><a href="qmapiterator.html#hasNext">hasNext</a>(), <a href="qmapiterator.html#next">next</a>(), and <a href="qmapiterator.html#peekPrevious">peekPrevious</a>().</p>
<!-- @@@peekNext -->
<!-- $$$peekPrevious[overload1]$$$peekPrevious -->
<h3 class="fn" id="peekPrevious"><a name="peekPrevious"></a><span class="type">Item</span> QMapIterator::<span class="name">peekPrevious</span>() const</h3>
<p>Returns the previous item without moving the iterator.</p>
<p>Call <a href="qmapiterator.html#key">key</a>() on the return value to obtain the item's key, and <a href="qmapiterator.html#value">value</a>() to obtain the value.</p>
<p>Calling this function on an iterator located at the front of the container leads to undefined results.</p>
<p><b>See also </b><a href="qmapiterator.html#hasPrevious">hasPrevious</a>(), <a href="qmapiterator.html#previous">previous</a>(), and <a href="qmapiterator.html#peekNext">peekNext</a>().</p>
<!-- @@@peekPrevious -->
<!-- $$$previous[overload1]$$$previous -->
<h3 class="fn" id="previous"><a name="previous"></a><span class="type">Item</span> QMapIterator::<span class="name">previous</span>()</h3>
<p>Returns the previous item and moves the iterator back by one position.</p>
<p>Call <a href="qmapiterator.html#key">key</a>() on the return value to obtain the item's key, and <a href="qmapiterator.html#value">value</a>() to obtain the value.</p>
<p>Calling this function on an iterator located at the front of the container leads to undefined results.</p>
<p><b>See also </b><a href="qmapiterator.html#hasPrevious">hasPrevious</a>(), <a href="qmapiterator.html#peekPrevious">peekPrevious</a>(), and <a href="qmapiterator.html#next">next</a>().</p>
<!-- @@@previous -->
<!-- $$$toBack[overload1]$$$toBack -->
<h3 class="fn" id="toBack"><a name="toBack"></a><span class="type">void</span> QMapIterator::<span class="name">toBack</span>()</h3>
<p>Moves the iterator to the back of the container (after the last item).</p>
<p><b>See also </b><a href="qmapiterator.html#toFront">toFront</a>() and <a href="qmapiterator.html#previous">previous</a>().</p>
<!-- @@@toBack -->
<!-- $$$toFront[overload1]$$$toFront -->
<h3 class="fn" id="toFront"><a name="toFront"></a><span class="type">void</span> QMapIterator::<span class="name">toFront</span>()</h3>
<p>Moves the iterator to the front of the container (before the first item).</p>
<p><b>See also </b><a href="qmapiterator.html#toBack">toBack</a>() and <a href="qmapiterator.html#next">next</a>().</p>
<!-- @@@toFront -->
<!-- $$$value[overload1]$$$value -->
<h3 class="fn" id="value"><a name="value"></a>const <span class="type">T</span> &QMapIterator::<span class="name">value</span>() const</h3>
<p>Returns the value of the last item that was jumped over using one of the traversal functions (<a href="qmapiterator.html#next">next</a>(), <a href="qmapiterator.html#previous">previous</a>(), <a href="qmapiterator.html#findNext">findNext</a>(), <a href="qmapiterator.html#findPrevious">findPrevious</a>()).</p>
<p>After a call to <a href="qmapiterator.html#next">next</a>() or <a href="qmapiterator.html#findNext">findNext</a>(), value() is equivalent to <a href="qmapiterator.html#peekPrevious">peekPrevious</a>().value(). After a call to <a href="qmapiterator.html#previous">previous</a>() or <a href="qmapiterator.html#findPrevious">findPrevious</a>(), value() is equivalent to <a href="qmapiterator.html#peekNext">peekNext</a>().value().</p>
<p><b>See also </b><a href="qmapiterator.html#key">key</a>().</p>
<!-- @@@value -->
<!-- $$$operator=[overload1]$$$operator=constQMap<Key,T>& -->
<h3 class="fn" id="operator-eq"><a name="operator-eq"></a><span class="type"><a href="qmapiterator.html#QMapIterator">QMapIterator</a></span> &QMapIterator::<span class="name">operator=</span>(const <span class="type"><a href="qmap.html">QMap</a></span><<span class="type">Key</span>, <span class="type">T</span>> &<i>map</i>)</h3>
<p>Makes the iterator operate on <i>map</i>. The iterator is set to be at the front of the map (before the first item).</p>
<p><b>See also </b><a href="qmapiterator.html#toFront">toFront</a>() and <a href="qmapiterator.html#toBack">toBack</a>().</p>
<!-- @@@operator= -->
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