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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 >QFutureIterator</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">QFutureIterator Class</h1>
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<p>The <a href="qfutureiterator.html">QFutureIterator</a> class provides a Java-style const iterator for <a href="qfuture.html">QFuture</a>. <a href="#details">More...</a></p>
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<tr><td class="memItemLeft rightAlign topAlign"> Header:</td><td class="memItemRight bottomAlign"> <span class="preprocessor">#include <QFutureIterator></span>
</td></tr><tr><td class="memItemLeft rightAlign topAlign"> qmake:</td><td class="memItemRight bottomAlign"> QT += core</td></tr><tr><td class="memItemLeft rightAlign topAlign"> Since:</td><td class="memItemRight bottomAlign"> Qt 4.4</td></tr></table></div><ul>
<li><a href="qfutureiterator-members.html">List of all members, including inherited members</a></li>
</ul>
<p><b>Note:</b> All functions in this class are reentrant.</p>
<a name="public-functions"></a>
<h2 id="public-functions">Public Functions</h2>
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<tr><td class="memItemLeft rightAlign topAlign"> </td><td class="memItemRight bottomAlign"><b><a href="qfutureiterator.html#QFutureIterator">QFutureIterator</a></b>(const QFuture<T> &<i>future</i>)</td></tr>
<tr><td class="memItemLeft rightAlign topAlign"> bool </td><td class="memItemRight bottomAlign"><b><a href="qfutureiterator.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="qfutureiterator.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="qfutureiterator.html#hasNext">hasNext</a></b>() const</td></tr>
<tr><td class="memItemLeft rightAlign topAlign"> bool </td><td class="memItemRight bottomAlign"><b><a href="qfutureiterator.html#hasPrevious">hasPrevious</a></b>() const</td></tr>
<tr><td class="memItemLeft rightAlign topAlign"> const T &</td><td class="memItemRight bottomAlign"><b><a href="qfutureiterator.html#next">next</a></b>()</td></tr>
<tr><td class="memItemLeft rightAlign topAlign"> const T &</td><td class="memItemRight bottomAlign"><b><a href="qfutureiterator.html#peekNext">peekNext</a></b>() const</td></tr>
<tr><td class="memItemLeft rightAlign topAlign"> const T &</td><td class="memItemRight bottomAlign"><b><a href="qfutureiterator.html#peekPrevious">peekPrevious</a></b>() const</td></tr>
<tr><td class="memItemLeft rightAlign topAlign"> const T &</td><td class="memItemRight bottomAlign"><b><a href="qfutureiterator.html#previous">previous</a></b>()</td></tr>
<tr><td class="memItemLeft rightAlign topAlign"> void </td><td class="memItemRight bottomAlign"><b><a href="qfutureiterator.html#toBack">toBack</a></b>()</td></tr>
<tr><td class="memItemLeft rightAlign topAlign"> void </td><td class="memItemRight bottomAlign"><b><a href="qfutureiterator.html#toFront">toFront</a></b>()</td></tr>
<tr><td class="memItemLeft rightAlign topAlign"> QFutureIterator &</td><td class="memItemRight bottomAlign"><b><a href="qfutureiterator.html#operator-eq">operator=</a></b>(const QFuture<T> &<i>future</i>)</td></tr>
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<a name="details"></a>
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<div class="descr">
<h2 id="details">Detailed Description</h2>
<p>The <a href="qfutureiterator.html">QFutureIterator</a> class provides a Java-style const iterator for <a href="qfuture.html">QFuture</a>.</p>
<p><a href="qfuture.html">QFuture</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>An alternative to using iterators is to use index positions. Some <a href="qfuture.html">QFuture</a> member functions take an index as their first parameter, making it possible to access results without using iterators.</p>
<p><a href="qfutureiterator.html">QFutureIterator</a><T> allows you to iterate over a <a href="qfuture.html">QFuture</a><T>. Note that there is no mutable iterator for <a href="qfuture.html">QFuture</a> (unlike the other Java-style iterators).</p>
<p>The <a href="qfutureiterator.html">QFutureIterator</a> constructor takes a <a href="qfuture.html">QFuture</a> as its argument. After construction, the iterator is located at the very beginning of the result list (i.e. before the first result). Here's how to iterate over all the results sequentially:</p>
<pre class="cpp">
<span class="type"><a href="qfuture.html">QFuture</a></span><span class="operator"><</span><span class="type"><a href="qstring.html">QString</a></span><span class="operator">></span> future;
<span class="operator">.</span><span class="operator">.</span><span class="operator">.</span>
<span class="type"><a href="qfutureiterator.html#QFutureIterator">QFutureIterator</a></span><span class="operator"><</span><span class="type"><a href="qstring.html">QString</a></span><span class="operator">></span> i(future);
<span class="keyword">while</span> (i<span class="operator">.</span>hasNext())
<a href="qtglobal.html#qDebug">qDebug</a>() <span class="operator"><</span><span class="operator"><</span> i<span class="operator">.</span>next();
</pre>
<p>The <a href="qfutureiterator.html#next">next</a>() function returns the next result (waiting for it to become available, if necessary) from the future and advances the iterator. Unlike STL-style iterators, Java-style iterators point <i>between</i> results rather than directly <i>at</i> results. The first call to <a href="qfutureiterator.html#next">next</a>() advances the iterator to the position between the first and second result, and returns the first result; the second call to <a href="qfutureiterator.html#next">next</a>() advances the iterator to the position between the second and third result, and returns the second result; 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="qfutureiterator.html#QFutureIterator">QFutureIterator</a></span><span class="operator"><</span><span class="type"><a href="qstring.html">QString</a></span><span class="operator">></span> i(future);
i<span class="operator">.</span>toBack();
<span class="keyword">while</span> (i<span class="operator">.</span>hasPrevious())
<a href="qtglobal.html#qDebug">qDebug</a>() <span class="operator"><</span><span class="operator"><</span> i<span class="operator">.</span>previous();
</pre>
<p>If you want to find all occurrences of a particular value, use <a href="qfutureiterator.html#findNext">findNext</a>() or <a href="qfutureiterator.html#findPrevious">findPrevious</a>() in a loop.</p>
<p>Multiple iterators can be used on the same future. If the future is modified while a <a href="qfutureiterator.html">QFutureIterator</a> is active, the <a href="qfutureiterator.html">QFutureIterator</a> will continue iterating over the original future, ignoring the modified copy.</p>
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<p><b>See also </b><a href="qfuture-const-iterator.html">QFuture::const_iterator</a> and <a href="qfuture.html">QFuture</a>.</p>
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<div class="func">
<h2>Member Function Documentation</h2>
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<h3 class="fn" id="QFutureIterator"><a name="QFutureIterator"></a>QFutureIterator::<span class="name">QFutureIterator</span>(const <span class="type"><a href="qfuture.html">QFuture</a></span><<span class="type">T</span>> &<i>future</i>)</h3>
<p>Constructs an iterator for traversing <i>future</i>. The iterator is set to be at the front of the result list (before the first result).</p>
<p><b>See also </b><a href="qfutureiterator.html#operator-eq">operator=</a>().</p>
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<h3 class="fn" id="findNext"><a name="findNext"></a><span class="type">bool</span> QFutureIterator::<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 <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 result; otherwise, the iterator is positioned at the back of the result list.</p>
<p><b>See also </b><a href="qfutureiterator.html#findPrevious">findPrevious</a>().</p>
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<!-- $$$findPrevious[overload1]$$$findPreviousconstT& -->
<h3 class="fn" id="findPrevious"><a name="findPrevious"></a><span class="type">bool</span> QFutureIterator::<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 <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 result; otherwise, the iterator is positioned at the front of the result list.</p>
<p><b>See also </b><a href="qfutureiterator.html#findNext">findNext</a>().</p>
<!-- @@@findPrevious -->
<!-- $$$hasNext[overload1]$$$hasNext -->
<h3 class="fn" id="hasNext"><a name="hasNext"></a><span class="type">bool</span> QFutureIterator::<span class="name">hasNext</span>() const</h3>
<p>Returns <code>true</code> if there is at least one result ahead of the iterator, e.g., the iterator is <i>not</i> at the back of the result list; otherwise returns false.</p>
<p><b>See also </b><a href="qfutureiterator.html#hasPrevious">hasPrevious</a>() and <a href="qfutureiterator.html#next">next</a>().</p>
<!-- @@@hasNext -->
<!-- $$$hasPrevious[overload1]$$$hasPrevious -->
<h3 class="fn" id="hasPrevious"><a name="hasPrevious"></a><span class="type">bool</span> QFutureIterator::<span class="name">hasPrevious</span>() const</h3>
<p>Returns <code>true</code> if there is at least one result ahead of the iterator, e.g., the iterator is <i>not</i> at the front of the result list; otherwise returns false.</p>
<p><b>See also </b><a href="qfutureiterator.html#hasNext">hasNext</a>() and <a href="qfutureiterator.html#previous">previous</a>().</p>
<!-- @@@hasPrevious -->
<!-- $$$next[overload1]$$$next -->
<h3 class="fn" id="next"><a name="next"></a>const <span class="type">T</span> &QFutureIterator::<span class="name">next</span>()</h3>
<p>Returns the next result and advances the iterator by one position.</p>
<p>Calling this function on an iterator located at the back of the result list leads to undefined results.</p>
<p><b>See also </b><a href="qfutureiterator.html#hasNext">hasNext</a>(), <a href="qfutureiterator.html#peekNext">peekNext</a>(), and <a href="qfutureiterator.html#previous">previous</a>().</p>
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<h3 class="fn" id="peekNext"><a name="peekNext"></a>const <span class="type">T</span> &QFutureIterator::<span class="name">peekNext</span>() const</h3>
<p>Returns the next result without moving the iterator.</p>
<p>Calling this function on an iterator located at the back of the result list leads to undefined results.</p>
<p><b>See also </b><a href="qfutureiterator.html#hasNext">hasNext</a>(), <a href="qfutureiterator.html#next">next</a>(), and <a href="qfutureiterator.html#peekPrevious">peekPrevious</a>().</p>
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<!-- $$$peekPrevious[overload1]$$$peekPrevious -->
<h3 class="fn" id="peekPrevious"><a name="peekPrevious"></a>const <span class="type">T</span> &QFutureIterator::<span class="name">peekPrevious</span>() const</h3>
<p>Returns the previous result without moving the iterator.</p>
<p>Calling this function on an iterator located at the front of the result list leads to undefined results.</p>
<p><b>See also </b><a href="qfutureiterator.html#hasPrevious">hasPrevious</a>(), <a href="qfutureiterator.html#previous">previous</a>(), and <a href="qfutureiterator.html#peekNext">peekNext</a>().</p>
<!-- @@@peekPrevious -->
<!-- $$$previous[overload1]$$$previous -->
<h3 class="fn" id="previous"><a name="previous"></a>const <span class="type">T</span> &QFutureIterator::<span class="name">previous</span>()</h3>
<p>Returns the previous result and moves the iterator back by one position.</p>
<p>Calling this function on an iterator located at the front of the result list leads to undefined results.</p>
<p><b>See also </b><a href="qfutureiterator.html#hasPrevious">hasPrevious</a>(), <a href="qfutureiterator.html#peekPrevious">peekPrevious</a>(), and <a href="qfutureiterator.html#next">next</a>().</p>
<!-- @@@previous -->
<!-- $$$toBack[overload1]$$$toBack -->
<h3 class="fn" id="toBack"><a name="toBack"></a><span class="type">void</span> QFutureIterator::<span class="name">toBack</span>()</h3>
<p>Moves the iterator to the back of the result list (after the last result).</p>
<p><b>See also </b><a href="qfutureiterator.html#toFront">toFront</a>() and <a href="qfutureiterator.html#previous">previous</a>().</p>
<!-- @@@toBack -->
<!-- $$$toFront[overload1]$$$toFront -->
<h3 class="fn" id="toFront"><a name="toFront"></a><span class="type">void</span> QFutureIterator::<span class="name">toFront</span>()</h3>
<p>Moves the iterator to the front of the result list (before the first result).</p>
<p><b>See also </b><a href="qfutureiterator.html#toBack">toBack</a>() and <a href="qfutureiterator.html#next">next</a>().</p>
<!-- @@@toFront -->
<!-- $$$operator=[overload1]$$$operator=constQFuture<T>& -->
<h3 class="fn" id="operator-eq"><a name="operator-eq"></a><span class="type"><a href="qfutureiterator.html#QFutureIterator">QFutureIterator</a></span> &QFutureIterator::<span class="name">operator=</span>(const <span class="type"><a href="qfuture.html">QFuture</a></span><<span class="type">T</span>> &<i>future</i>)</h3>
<p>Makes the iterator operate on <i>future</i>. The iterator is set to be at the front of the result list (before the first result).</p>
<p><b>See also </b><a href="qfutureiterator.html#toFront">toFront</a>() and <a href="qfutureiterator.html#toBack">toBack</a>().</p>
<!-- @@@operator= -->
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