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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN"><html><head><meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1">
<title>Qt Toolkit - QMap Class</title><style type="text/css"><!--
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<h1 align=center>QMap Class Reference</h1><br clear="all">
<p>
The QMap class is a value based template class that provides a dictionary
<a href="#details">More...</a>
<p>
<code>#include <<a href="qmap-h.html">qmap.h</a>></code>
<p><a href="qmap-members.html">List of all member functions.</a>
<h2>Public Members</h2>
<ul>
<li><div class="fn"><a href="#3cfcf4"><b>QMap</b></a>()</div>
<li><div class="fn"><a href="#b893ab"><b>QMap</b></a>(constQMap<Key,T>&m)</div>
<li><div class="fn"><a href="#6c41e3"><b>~QMap</b></a>()</div>
<li><div class="fn">QMap<Key, T>&<a href="#e2c5fc"><b>operator=</b></a>(constQMap<Key, T>&m)</div>
<li><div class="fn">Iterator<a href="#4aaaf0"><b>begin</b></a>()</div>
<li><div class="fn">Iterator<a href="#ecaed1"><b>end</b></a>()</div>
<li><div class="fn">ConstIterator<a href="#9bed46"><b>begin</b></a>()const</div>
<li><div class="fn">ConstIterator<a href="#534f76"><b>end</b></a>()const</div>
<li><div class="fn">Iterator<a href="#fa2738"><b>find</b></a>(constKey&k)</div>
<li><div class="fn">ConstIterator<a href="#12d6cb"><b>find</b></a>(constKey&k)const</div>
<li><div class="fn">T&<a href="#df2d45"><b>operator[]</b></a>(constKey&k)</div>
<li><div class="fn">constT&<a href="#961225"><b>operator[]</b></a>(constKey&k)const</div>
<li><div class="fn">bool<a href="#32b0f6"><b>contains</b></a>(constKey&k)const</div>
<li><div class="fn">uint<a href="#31e76e"><b>count</b></a>()const</div>
<li><div class="fn">bool<a href="#e636aa"><b>isEmpty</b></a>()const</div>
<li><div class="fn">Iterator<a href="#3a71b8"><b>insert</b></a>(constKey&key, constT&value)</div>
<li><div class="fn">void<a href="#b9697e"><b>remove</b></a>(Iteratorit)</div>
<li><div class="fn">void<a href="#5f0d58"><b>remove</b></a>(constKey&k)</div>
<li><div class="fn">Iterator<a href="#073009"><b>replace</b></a>(constKey&k, constT&v)</div>
<li><div class="fn">void<a href="#ad52f8"><b>clear</b></a>()</div>
</ul>
<h2>Protected Members</h2>
<ul>
<li><div class="fn">void<a href="#fafe7a"><b>detach</b></a>()</div>
</ul>
<h2>Related Functions</h2>
(Note that these are not member functions.)
<ul>
<li>QDataStream& <a href="qmap.html#4c3cf5"><b>operator>></b></a> (QDataStream & s, QMap<Key,T> & m)
<li>QDataStream& <a href="qmap.html#852287"><b>operator<<</b></a> (QDataStream & s, const QMap<Key,T> & m)
</ul>
<hr><h2><a name="details"></a>Detailed Description</h2>
The QMap class is a value based template class that provides a dictionary
<p>
Define a template instance QMap<Key,Data> to create a dictionary
with keys of type Key and values of type Data. QMap does not store
pointers to the members of the map. Instead, it holds a copy of
every member. For that reason this kind of classes is called "value
based" while <a href="qlist.html">QList</a> and <a href="qdict.html">QDict</a> are "reference based".
<p>Some classes can not be used within a QMap, for example everything
derived from <a href="qobject.html">QObject</a> and thus all classes that implement widgets.
Only values can be used in a QMap. To qualify as a value, the class
must provide
<ul>
<li>a copy constructor,
<li>an assignment operator and
<li> a default constructor, i.e. a constructor that does not take any arguments.
</ul>
<p>Note that C++ defaults to field-by-field assignment operators and
copy constructors if no explicit version is supplied. In many cases,
this is sufficient.
<p>The class used for the key requires that the <code>operator<</code> is implemented
and defines a total order on the keys.
<p>Example:
<pre> #include <qmap.h>
#include <qstring.h>
#include <stdio.h>
class Employee
{
public:
Employee(): s(0) {}
Employee( const QString& name, int salary )
: n(name), s(salary)
{}
<a href="qstring.html">QString</a> name() const { return n; }
int salary() const { return s; }
void setSalary( int salary ) { s = salary; }
private:
<a href="qstring.html">QString</a> n;
int s;
};
void main()
{
typedef QMap<<a href="qstring.html">QString</a>,Employee> EmployeeMap;
EmployeeMap map; // map of Employee
map.insert( "Gates", Employee("Bill", 50000) );
map.insert( "Ballmer", Employee("Steve",80000) );
map.insert( "Sommer,", Employee("Ron", 60000) );
Employee joe( "Joe", 50000 );
map.insert( "Doe", joe );
joe.setSalary( 4000 );
EmployeeMap::Iterator it;
for( it = map.begin(); it != map.end(); ++it )
printf( "%s, %s earns %d\n", it.key().latin1(), it.data().name().latin1(), it.data().salary() );
}
</pre>
<p>Program output:
<pre> Ballmer, Steve earns 80000
Doe, Joe earns 50000
Gates, Bill earns 50000
Sommer, Ron earns 60000
</pre>
<p>As you can see, the latest changes to Joe's salary did not affect the value
in the list because the map created a copy of Joe's entry. In addition you
should notice that the items are alphabetically sorted when iterating
over the map.
<p>There are two ways to find values in the list. The first one is to use
the <a href="#12d6cb">find</a>() function. It returns an iterator pointing to the desired
item or the <a href="#534f76">end</a>() iterator it no such element exists.
<p>The second approach uses the operator[]. But be warned: If you don't know
that the element you are searching for is really in the list, then you
should not use operator[]. The following example illustrates that.
<p><pre> <a href="qmap.html">QMap</a><<a href="qstring.html">QString</a>,QString> map;
map.<a href="#3a71b8">insert</a>( "Weis", "Torben" );
str << map["Weis"] << map["Ettrich"] << endl;
const QMap<<a href="qstring.html">QString</a>,QString>& map2 = map;
str << map2["Weis"] << map2["Reggie"] << endl;
</pre>
<p>The code fragment will print out "Torben", "" and the second part will
print "Torben", "". In addition the first fragment inserted an empty entry
with key "Ettrich". The second one did not insert an empty entry with
key "Reggie" because the const operator[] was used which can not do insertion.
So if you are not sure whether a certain element is in the map you should
use find() and iterators.
<p>If you just want to know whether a certain key is contained in the map,
the the <a href="#32b0f6">contains</a>() function is what you are looking for. In addition <a href="#31e76e">count</a>()
tells you how many keys there are currently in the map.
<p>Another method for traversing a map is to use the functions <a href="#4aaaf0">begin</a>()
and end(). With a simple for loop as shown in the example you can
iterate over the complete map. It is safe to have multiple
iterators at the same time. If some member of the map is removed
then only iterators pointing to the removed member become
invalid. Inserting in the map does not invalidate any iterator.
<p>Since QMap is value based there is no need to care about deleting
elements in the list. The list holds its own copies and will free
them if the corresponding member or the list itself is deleted. You
can force the list to free all of its item with <a href="#ad52f8">clear</a>().
<p>QMap is implicitly shared. This means you can just make copies of
the map in time O(1). If multiple QMap instances share the same data
and one is modifying the map's data then this modifying instance
makes a copy and modifies its private copy - thus it does not affect
other instances. From a developer's point of view you can think
that a QMap and a copy of this map have nothing to do with each
other.
<p>There are two ways of inserting new elements in a list. One uses the
<a href="#3a71b8">insert</a>() method while the other one uses operator[] like this:
<p><pre> <a href="qmap.html">QMap</a><<a href="qstring.html">QString</a>,QString> map;
map["Weis"] = "Torben";
</pre>
;
<p>Items can be removed from the map in two ways. The first is to pass
an iterator to the <a href="#5f0d58">remove</a>(). The other possibility is to pass a key
value to remove() which will delete the entry with the requested
key. In addition you can clear the entire map using the clear()
method.
<p>See also <a href="qmapiterator.html">QMapIterator</a>.
<hr><h2>Member Function Documentation</h2>
<h3 class="fn"><a name="3cfcf4"></a>QMap::QMap()</h3>
<p>Constructs an empty map.
<h3 class="fn"><a name="b893ab"></a>QMap::QMap(constQMap<Key,T>&m)</h3>
<p>Constructs a copy of <em>m.</em>
<p>This operation costs O(1) time since QMap is implicit shared. The
first instance applying modifications to a shared list will create a
copy which takes in turn O(<a href="n.html">n</a>) time. However returning a QMap from a
function is very fast.
<h3 class="fn"><a name="6c41e3"></a>QMap::~QMap()</h3>
<p>Destroys the map. References to the values in the map and all
iterators of this map become invalidated. Since QMap is highly tuned
for performance you won't see warnings if you use invalid iterators,
because it is impossible for an iterator to check whether it is
valid or not.
<h3 class="fn">ConstIterator<a name="9bed46"></a>QMap::begin()const</h3>
<p>Returns an iterator pointing to the first element in the map. This
iterator equals <a href="#534f76">end</a>() if the map is empty;
<p>See also <a href="#534f76">end</a>() and <a href="qmapconstiterator.html">QMapConstIterator</a>.
<h3 class="fn">Iterator<a name="4aaaf0"></a>QMap::begin()</h3>
<p>Returns an iterator pointing to the first element in the map. This
iterator equals <a href="#534f76">end</a>() if the map is empty;
<p>See also <a href="#534f76">end</a>() and <a href="qmapiterator.html">QMapIterator</a>.
<h3 class="fn">void<a name="ad52f8"></a>QMap::clear()</h3>
<p>Removes all items from the map.
<p>See also <a href="#5f0d58">remove</a>().
<h3 class="fn">bool<a name="32b0f6"></a>QMap::contains(constKey&k)const</h3>
<p>Returns TRUE if the key <em>k</em> is contained in the map.
<h3 class="fn">uint<a name="31e76e"></a>QMap::count()const</h3>
<p>Returns the number of items in the ap.
<p>See also <a href="#e636aa">isEmpty</a>().
<h3 class="fn">void<a name="fafe7a"></a>QMap::detach() <code>[protected]</code></h3>
<p>If the map does not share its data with another QMap instance, then
nothing happens, otherwise the function creates a new copy of this
data and detaches from the shared one. This function is called
whenever the map is modified. The implicit sharing mechanism is
implemented this way.
<h3 class="fn">ConstIterator<a name="534f76"></a>QMap::end()const</h3>
<p>Returns an iterator pointing behind the last element in the map. This
iterator equals <a href="#4aaaf0">begin</a>() if the map is empty.
<p>See also <a href="#4aaaf0">begin</a>() and <a href="qmapconstiterator.html">QMapConstIterator</a>.
<h3 class="fn">Iterator<a name="ecaed1"></a>QMap::end()</h3>
<p>Returns an iterator pointing behind the last element in the map. This
iterator equals <a href="#4aaaf0">begin</a>() if the map is empty.
<p>See also <a href="#4aaaf0">begin</a>() and <a href="qmapiterator.html">QMapIterator</a>.
<h3 class="fn">ConstIterator<a name="12d6cb"></a>QMap::find(constKey&k)const</h3>
<p>Finds the key <em>k</em> in the map.
<p>Returns <a href="#534f76">end</a>() if no key did match.
<p>See also <a href="qmapconstiterator.html">QMapConstIterator</a>.
<h3 class="fn">Iterator<a name="fa2738"></a>QMap::find(constKey&k)</h3>
<p>Finds the key <em>k</em> in the map.
<p>Returns <a href="#534f76">end</a>() if no key did match.
<p>See also <a href="qmapiterator.html">QMapIterator</a>.
<h3 class="fn">Iterator<a name="3a71b8"></a>QMap::insert(constKey&key, constT&value)</h3>
<p>Inserts the <em>value</em> with key <em>k.</em>
<p>Returns an iterator pointing at the inserted value.
<p>See also <a href="qmapiterator.html">QMapIterator</a>.
<h3 class="fn">bool<a name="e636aa"></a>QMap::isEmpty()const</h3>
<p>Returns TRUE if the list is empty, i.e. <a href="#31e76e">count</a>() == 0. Returns FALSE
otherwise.
<p>See also <a href="#31e76e">count</a>().
<h3 class="fn">QMap<Key, T>&<a name="e2c5fc"></a>QMap::operator=(constQMap<Key, T>&m)</h3>
<p>Assigns <em>m</em> to this map and returns a reference to this map.
<p>All iterators of the current map become invalidated by this
operation. The cost of such an assignment is O(1) since QMap is
implicitly shared.
<h3 class="fn">T&<a name="df2d45"></a>QMap::operator[](constKey&k)</h3>
<p>Returns the value associated with the key <em>k.</em> If no such
key is present then an empty item is inserted with this key
and a reference to the item is returned.
<p>You can use this operator in two directions: For reading and for
writing:
<p><pre> <a href="qmap.html">QMap</a><<a href="qstring.html">QString</a>,QString> map;
map[ "Weis" ] = "Torben";
stream << map[ "Weis" ];
</pre>
<h3 class="fn">constT&<a name="961225"></a>QMap::operator[](constKey&k)const</h3>
<p>Returns the value associated with the key <em>k.</em> If no such
key is present then a reference to an empty item is returned.
<h3 class="fn">void<a name="b9697e"></a>QMap::remove(Iteratorit)</h3>
<p>Removes the item at position <em>it</em> in the map.
<p>See also <a href="#ad52f8">clear</a>() and <a href="qmapiterator.html">QMapIterator</a>.
<h3 class="fn">void<a name="5f0d58"></a>QMap::remove(constKey&k)</h3>
<p>Removes the item with the key <em>k.</em>
<p>See also <a href="#ad52f8">clear</a>().
<h3 class="fn">Iterator<a name="073009"></a>QMap::replace(constKey&k, constT&v)</h3>
<p>Replaces the value with key <em>k</em> from the map if possible and
inserts the new value <em>v</em> with key <em>k</em> in the map.
<p>See also <a href="#3a71b8">insert</a>(), <a href="#5f0d58">remove</a>() and <a href="qmapiterator.html">QMapIterator</a>.
<hr><h2>Related Functions</h2>
<h3><a href="qdatastream.html">QDataStream</a>& <a name="4c3cf5"></a>operator>> (<a href="qdatastream.html">QDataStream</a> & s, QMap<Key,T> & m)</h3>
<p>Reads a map from the stream. The types <em>Key</em> and <em>T</em> must implement
the streaming operator, too.
<h3><a href="qdatastream.html">QDataStream</a>& <a name="852287"></a>operator<< (<a href="qdatastream.html">QDataStream</a> & s, const QMap<Key,T> & m)</h3>
<p>Writes a map to the stream. The types <em>Key</em> and <em>T</em> must implement
the streaming operator, too.
<hr><p>
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