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<td align="right" valign="top" width="230"><img src="images/trolltech-logo.png" align="right" width="203" height="32" border="0" /></td></tr></table><h1 align="center">QHash::iterator Class Reference<br /><sup><sup>[<a href="qtcore.html">QtCore</a> module]</sup></sup></h1>

<td align="right" valign="top" width="230"><a href="http://www.trolltech.com"><img src="images/trolltech-logo.png" align="right" width="203" height="32" border="0" /></a></td></tr></table><h1 align="center">QHash::iterator Class Reference<br /><sup><sup>[<a href="qtcore.html">QtCore</a> module]</sup></sup></h1>

<p>The QHash::iterator class provides an STL-style non-const iterator for <a href="qhash.html">QHash</a> and <a href="qmultihash.html">QMultiHash</a>. <a href="#details">More...</a></p>

<pre>#include <QHash></pre><ul>

<pre> #include <<a href="qhash.html">QHash</a>></pre><ul>

<li><a href="qhash-iterator-members.html">List of all members, including inherited members</a></li>

</ul>

<p><a href="qhash.html">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</a><Key, T>::iterator allows you to iterate over a <a href="qhash.html">QHash</a> (or <a href="qmultihash.html">QMultiHash</a>) and to modify the value (but not the key) associated with a particular key. If you want to iterate over a const <a href="qhash.html">QHash</a>, you should use <a href="qhash-const-iterator.html">QHash::const_iterator</a>. 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</a> as well, unless you need to change the <a href="qhash.html">QHash</a> through the iterator. Const iterators are slightly faster, and can improve code readability.</p>

<p>The default QHash::iterator constructor creates an uninitialized iterator. You must initialize it using a <a href="qhash.html">QHash</a> function like <a href="qhash.html#begin">QHash::begin</a>(), <a href="qhash.html#end">QHash::end</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>  QHash<QString, int> hash;

hash.insert("January", 1);

hash.insert("February", 2);

...

hash.insert("December", 12);

<pre> QHash<QString, int> hash;

hash.insert("January", 1);

hash.insert("February", 2);

...

hash.insert("December", 12);

QHash<QString, int>::iterator i;

for (i = hash.begin(); i != hash.end(); ++i)

cout << i.key() << ": " << i.value() << endl;</pre>

QHash<QString, int>::iterator i;

for (i = hash.begin(); i != hash.end(); ++i)

cout << i.key() << ": " << i.value() << endl;</pre>

<p>Unlike <a href="qmap.html">QMap</a>, which orders its items by key, <a href="qhash.html">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>Let's see a few examples of things we can do with a QHash::iterator that we cannot do with a <a href="qhash-const-iterator.html">QHash::const_iterator</a>. Here's an example that increments every value stored in the <a href="qhash.html">QHash</a> by 2:</p>

<pre>  QHash<QString, int>::iterator i;

for (i = hash.begin(); i != hash.end(); ++i)

i.value() += 2;</pre>

<pre> QHash<QString, int>::iterator i;

for (i = hash.begin(); i != hash.end(); ++i)

i.value() += 2;</pre>

<p>Here's an example that removes all the items whose key is a string that starts with an underscore character:</p>

<pre>  QHash<QString, int>::iterator i = hash.begin();

while (i != hash.end()) {

if (i.key().startsWith("_"))

i = hash.erase(i);

else

++i;

}</pre>

<pre> QHash<QString, int>::iterator i = hash.begin();

while (i != hash.end()) {

if (i.key().startsWith("_"))

i = hash.erase(i);

else

++i;

}</pre>

<p>The call to <a href="qhash.html#erase">QHash::erase</a>() removes the item pointed to by the iterator from the hash, and returns an iterator to the next item. Here's another way of removing an item while iterating:</p>

<pre>  QHash<QString, int>::iterator i = hash.begin();

while (i != hash.end()) {

QHash<QString, int>::iterator prev = i;

++i;

if (prev.key().startsWith("_"))

hash.erase(prev);

}</pre>

<pre> QHash<QString, int>::iterator i = hash.begin();

while (i != hash.end()) {

QHash<QString, int>::iterator prev = i;

++i;

if (prev.key().startsWith("_"))

hash.erase(prev);

}</pre>

<p>It might be tempting to write code like this:</p>

<pre>  // WRONG

while (i != hash.end()) {

if (i.key().startsWith("_"))

hash.erase(i);

++i;

}</pre>

<pre><span class="comment"> // WRONG</span>

while (i != hash.end()) {

if (i.key().startsWith("_"))

hash.erase(i);

++i;

}</pre>

<p>However, this will potentially crash in <tt>++i</tt>, because <tt>i</tt> is a dangling iterator after the call to <a href="qhash.html#erase">erase</a>().</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</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</a> to rehash its internal data structure. There is one notable exception: <a href="qhash.html#erase">QHash::erase</a>(). This function can safely be called while iterating, and won't affect the order of items in the hash. 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</a>.</p>

<p>See also <a href="qhash-const-iterator.html">QHash::const_iterator</a> and <a href="qmutablehashiterator.html">QMutableHashIterator</a>.</p>

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<h3 class="fn"><a name="value"></a>T & iterator::value () const</h3>

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<p>Returns a modifiable reference to the current item's value.</p>

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<p>You can change the value of an item by using value() on the left side of an assignment, for example:</p>

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<pre>  if (i.key() == "Hello")

108

i.value() = "Bonjour";</pre>

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<pre> if (i.key() == "Hello")

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i.value() = "Bonjour";</pre>

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<p>See also <a href="qhash-iterator.html#key">key</a>() and <a href="qhash-iterator.html#operator-2a">operator*</a>().</p>

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<h3 class="fn"><a name="operator-not-eq"></a>bool iterator::operator!= ( const iterator & <i>other</i> ) const</h3>

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<p>Returns true if <i>other</i> points to a different item than this iterator; otherwise returns false.</p>

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