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<td >Qt 5.12</td><td ><a href="qtcore-index.html">Qt Core</a></td><td ><a href="qtcore-module.html">C++ Classes</a></td><td >QHashIterator</td></tr></table><table class="buildversion"><tr>
<td id="buildversion" width="100%" align="right"><a href="qtcore-index.html">Qt 5.12.6 Reference Documentation</a></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">QHashIterator Class</h1>
<!-- $$$QHashIterator-brief -->
<p>The <a href="qhashiterator.html">QHashIterator</a> class provides a Java-style const iterator for <a href="qhash.html#qhash">QHash</a> and <a href="qmultihash.html">QMultiHash</a>. <a href="#details">More...</a></p>
<!-- @@@QHashIterator -->
<div class="table"><table class="alignedsummary">
<tr><td class="memItemLeft rightAlign topAlign"> Header:</td><td class="memItemRight bottomAlign"> <span class="preprocessor">#include <QHashIterator></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="qhashiterator-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="qhashiterator.html#QHashIterator">QHashIterator</a></b>(const QHash<Key, T> &<i>hash</i>)</td></tr>
<tr><td class="memItemLeft rightAlign topAlign"> bool </td><td class="memItemRight bottomAlign"><b><a href="qhashiterator.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="qhashiterator.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="qhashiterator.html#hasNext">hasNext</a></b>() const</td></tr>
<tr><td class="memItemLeft rightAlign topAlign"> bool </td><td class="memItemRight bottomAlign"><b><a href="qhashiterator.html#hasPrevious">hasPrevious</a></b>() const</td></tr>
<tr><td class="memItemLeft rightAlign topAlign"> const Key &</td><td class="memItemRight bottomAlign"><b><a href="qhashiterator.html#key">key</a></b>() const</td></tr>
<tr><td class="memItemLeft rightAlign topAlign"> QHashIterator::Item </td><td class="memItemRight bottomAlign"><b><a href="qhashiterator.html#next">next</a></b>()</td></tr>
<tr><td class="memItemLeft rightAlign topAlign"> QHashIterator::Item </td><td class="memItemRight bottomAlign"><b><a href="qhashiterator.html#peekNext">peekNext</a></b>() const</td></tr>
<tr><td class="memItemLeft rightAlign topAlign"> QHashIterator::Item </td><td class="memItemRight bottomAlign"><b><a href="qhashiterator.html#peekPrevious">peekPrevious</a></b>() const</td></tr>
<tr><td class="memItemLeft rightAlign topAlign"> QHashIterator::Item </td><td class="memItemRight bottomAlign"><b><a href="qhashiterator.html#previous">previous</a></b>()</td></tr>
<tr><td class="memItemLeft rightAlign topAlign"> void </td><td class="memItemRight bottomAlign"><b><a href="qhashiterator.html#toBack">toBack</a></b>()</td></tr>
<tr><td class="memItemLeft rightAlign topAlign"> void </td><td class="memItemRight bottomAlign"><b><a href="qhashiterator.html#toFront">toFront</a></b>()</td></tr>
<tr><td class="memItemLeft rightAlign topAlign"> const T &</td><td class="memItemRight bottomAlign"><b><a href="qhashiterator.html#value">value</a></b>() const</td></tr>
<tr><td class="memItemLeft rightAlign topAlign"> QHashIterator<Key, T> &</td><td class="memItemRight bottomAlign"><b><a href="qhashiterator.html#operator-eq">operator=</a></b>(const QHash<Key, T> &<i>container</i>)</td></tr>
</table></div>
<a name="details"></a>
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<div class="descr">
<h2 id="details">Detailed Description</h2>
<p>The <a href="qhashiterator.html">QHashIterator</a> class provides a Java-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> 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="qhashiterator.html">QHashIterator</a><Key, T> 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 hash as you iterate over it, use <a href="qmutablehashiterator.html">QMutableHashIterator</a> instead.</p>
<p>The <a href="qhashiterator.html">QHashIterator</a> constructor takes a <a href="qhash.html#qhash">QHash</a> as argument. After construction, the iterator is located at the very beginning of the hash (before the first item). Here's how to iterate over all the elements sequentially:</p>
<pre class="cpp">
<span class="type"><a href="qhash.html">QHash</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> hash;
<span class="operator">.</span><span class="operator">.</span><span class="operator">.</span>
<span class="type"><a href="qhashiterator.html#QHashIterator">QHashIterator</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(hash);
<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="qhashiterator.html#next">next</a>() function returns the next item in the hash and advances the iterator. The <a href="qhashiterator.html#key">key</a>() and <a href="qhashiterator.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="qhashiterator.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="qhashiterator.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="qhashiterator.html#QHashIterator">QHashIterator</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(hash);
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="qhashiterator.html#findNext">findNext</a>() or <a href="qhashiterator.html#findPrevious">findPrevious</a>() in a loop. For example:</p>
<pre class="cpp">
<span class="type"><a href="qhashiterator.html#QHashIterator">QHashIterator</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(hash);
<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 hash. If the hash is modified while a <a href="qhashiterator.html">QHashIterator</a> is active, the <a href="qhashiterator.html">QHashIterator</a> will continue iterating over the original hash, ignoring the modified copy.</p>
</div>
<p><b>See also </b><a href="qmutablehashiterator.html">QMutableHashIterator</a> and <a href="qhash-const-iterator.html">QHash::const_iterator</a>.</p>
<!-- @@@QHashIterator -->
<div class="func">
<h2>Member Function Documentation</h2>
<!-- $$$ -->
<h3 class="fn fngroupitem" id="findPrevious"><a name="findPrevious"></a><span class="type">bool</span> QHashIterator::<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="qhashiterator.html#findNext">findNext</a>().</p>
<!-- @@@ -->
<!-- $$$ -->
<h3 class="fn fngroupitem" id="findNext"><a name="findNext"></a><span class="type">bool</span> QHashIterator::<span class="name">findNext</span>(const <span class="type">T</span> &<i>value</i>)</h3>
<p>Searches for <i>value</i> starting from the current iterator position forward. Returns <code>true</code> if a (key, value) pair with value <i>value</i> is found; otherwise returns <code>false</code>.</p>
<p>After the call, if <i>value</i> was found, the iterator is positioned just after the matching item; otherwise, the iterator is positioned at the back of the container.</p>
<p><b>See also </b><a href="qhashiterator.html#findPrevious">findPrevious</a>().</p>
<!-- @@@ -->
<!-- $$$ -->
<h3 class="fn fngroupitem" id="key"><a name="key"></a>const <span class="type">Key</span> &QHashIterator::<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="qhashiterator.html#next">next</a>(), <a href="qhashiterator.html#previous">previous</a>(), <a href="qhashiterator.html#findNext">findNext</a>(), <a href="qhashiterator.html#findPrevious">findPrevious</a>()).</p>
<p>After a call to <a href="qhashiterator.html#next">next</a>() or <a href="qhashiterator.html#findNext">findNext</a>(), <a href="qhashiterator.html#key">key</a>() is equivalent to <a href="qhashiterator.html#peekPrevious">peekPrevious</a>().<a href="qhashiterator.html#key">key</a>(). After a call to <a href="qhashiterator.html#previous">previous</a>() or <a href="qhashiterator.html#findPrevious">findPrevious</a>(), <a href="qhashiterator.html#key">key</a>() is equivalent to <a href="qhashiterator.html#peekNext">peekNext</a>().<a href="qhashiterator.html#key">key</a>().</p>
<p><b>See also </b><a href="qhashiterator.html#value">value</a>().</p>
<!-- @@@ -->
<!-- $$$ -->
<h3 class="fn fngroupitem" id="value"><a name="value"></a>const <span class="type">T</span> &QHashIterator::<span class="name">value</span>() const</h3>
<p>Returns the value of the last item that was jumped over using one of the traversal functions (<a href="qhashiterator.html#next">next</a>(), <a href="qhashiterator.html#previous">previous</a>(), <a href="qhashiterator.html#findNext">findNext</a>(), <a href="qhashiterator.html#findPrevious">findPrevious</a>()).</p>
<p>After a call to <a href="qhashiterator.html#next">next</a>() or <a href="qhashiterator.html#findNext">findNext</a>(), <a href="qhashiterator.html#value">value</a>() is equivalent to <a href="qhashiterator.html#peekPrevious">peekPrevious</a>().<a href="qhashiterator.html#value">value</a>(). After a call to <a href="qhashiterator.html#previous">previous</a>() or <a href="qhashiterator.html#findPrevious">findPrevious</a>(), <a href="qhashiterator.html#value">value</a>() is equivalent to <a href="qhashiterator.html#peekNext">peekNext</a>().<a href="qhashiterator.html#value">value</a>().</p>
<p><b>See also </b><a href="qhashiterator.html#key">key</a>().</p>
<!-- @@@ -->
<!-- $$$ -->
<h3 class="fn fngroupitem" id="peekPrevious"><a name="peekPrevious"></a><span class="type">QHashIterator::Item</span> QHashIterator::<span class="name">peekPrevious</span>() const</h3>
<p>Returns the previous item without moving the iterator.</p>
<p>Call <a href="qhashiterator.html#key">key</a>() on the return value to obtain the item's key, and <a href="qhashiterator.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="qhashiterator.html#hasPrevious">hasPrevious</a>(), <a href="qhashiterator.html#previous">previous</a>(), and <a href="qhashiterator.html#peekNext">peekNext</a>().</p>
<!-- @@@ -->
<!-- $$$ -->
<h3 class="fn fngroupitem" id="previous"><a name="previous"></a><span class="type">QHashIterator::Item</span> QHashIterator::<span class="name">previous</span>()</h3>
<p>Returns the previous item and moves the iterator back by one position.</p>
<p>Call <a href="qhashiterator.html#key">key</a>() on the return value to obtain the item's key, and <a href="qhashiterator.html#value">value</a>() to obtain the value.</p>
<p>Calling this function on an iterator located at the front of the container leads to undefined results.</p>
<p><b>See also </b><a href="qhashiterator.html#hasPrevious">hasPrevious</a>(), <a href="qhashiterator.html#peekPrevious">peekPrevious</a>(), and <a href="qhashiterator.html#next">next</a>().</p>
<!-- @@@ -->
<!-- $$$ -->
<h3 class="fn fngroupitem" id="hasPrevious"><a name="hasPrevious"></a><span class="type">bool</span> QHashIterator::<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="qhashiterator.html#hasNext">hasNext</a>() and <a href="qhashiterator.html#previous">previous</a>().</p>
<!-- @@@ -->
<!-- $$$ -->
<h3 class="fn fngroupitem" id="peekNext"><a name="peekNext"></a><span class="type">QHashIterator::Item</span> QHashIterator::<span class="name">peekNext</span>() const</h3>
<p>Returns the next item without moving the iterator.</p>
<p>Call <a href="qhashiterator.html#key">key</a>() on the return value to obtain the item's key, and <a href="qhashiterator.html#value">value</a>() to obtain the value.</p>
<p>Calling this function on an iterator located at the back of the container leads to undefined results.</p>
<p><b>See also </b><a href="qhashiterator.html#hasNext">hasNext</a>(), <a href="qhashiterator.html#next">next</a>(), and <a href="qhashiterator.html#peekPrevious">peekPrevious</a>().</p>
<!-- @@@ -->
<!-- $$$ -->
<h3 class="fn fngroupitem" id="next"><a name="next"></a><span class="type">QHashIterator::Item</span> QHashIterator::<span class="name">next</span>()</h3>
<p>Returns the next item and advances the iterator by one position.</p>
<p>Call <a href="qhashiterator.html#key">key</a>() on the return value to obtain the item's key, and <a href="qhashiterator.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="qhashiterator.html#hasNext">hasNext</a>(), <a href="qhashiterator.html#peekNext">peekNext</a>(), and <a href="qhashiterator.html#previous">previous</a>().</p>
<!-- @@@ -->
<!-- $$$ -->
<h3 class="fn fngroupitem" id="hasNext"><a name="hasNext"></a><span class="type">bool</span> QHashIterator::<span class="name">hasNext</span>() const</h3>
<p>Returns <code>true</code> if there is at least one item ahead of the iterator, i.e. the iterator is <i>not</i> at the back of the container; otherwise returns <code>false</code>.</p>
<p><b>See also </b><a href="qhashiterator.html#hasPrevious">hasPrevious</a>() and <a href="qhashiterator.html#next">next</a>().</p>
<!-- @@@ -->
<!-- $$$ -->
<h3 class="fn fngroupitem" id="toBack"><a name="toBack"></a><span class="type">void</span> QHashIterator::<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="qhashiterator.html#toFront">toFront</a>() and <a href="qhashiterator.html#previous">previous</a>().</p>
<!-- @@@ -->
<!-- $$$ -->
<h3 class="fn fngroupitem" id="toFront"><a name="toFront"></a><span class="type">void</span> QHashIterator::<span class="name">toFront</span>()</h3>
<p>Moves the iterator to the front of the container (before the first item).</p>
<p><b>See also </b><a href="qhashiterator.html#toBack">toBack</a>() and <a href="qhashiterator.html#next">next</a>().</p>
<!-- @@@ -->
<!-- $$$ -->
<h3 class="fn fngroupitem" id="operator-eq"><a name="operator-eq"></a><span class="type"><a href="qhashiterator.html#QHashIterator">QHashIterator</a></span><<span class="type">Key</span>, <span class="type">T</span>> &QHashIterator::<span class="name">operator=</span>(const <span class="type"><a href="qhash.html">QHash</a></span><<span class="type">Key</span>, <span class="type">T</span>> &<i>container</i>)</h3>
<p>Makes the iterator operate on <i>hash</i>. The iterator is set to be at the front of the hash (before the first item).</p>
<p><b>See also </b><a href="qhashiterator.html#toFront">toFront</a>() and <a href="qhashiterator.html#toBack">toBack</a>().</p>
<!-- @@@ -->
<!-- $$$ -->
<h3 class="fn fngroupitem" id="QHashIterator"><a name="QHashIterator"></a>QHashIterator::<span class="name">QHashIterator</span>(const <span class="type"><a href="qhash.html">QHash</a></span><<span class="type">Key</span>, <span class="type">T</span>> &<i>hash</i>)</h3>
<p>Constructs an iterator for traversing <i>hash</i>. The iterator is set to be at the front of the hash (before the first item).</p>
<p><b>See also </b><a href="qhashiterator.html#operator-eq">operator=</a>().</p>
<!-- @@@ -->
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