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<td align="right" valign="center"><img src="logo32.png" align="right" width="64" height="32" border="0"></td></tr></table><h1 align=center>Collection Classes</h1>
<p> <!-- index collection classes --><a name="collection-classes"></a><!-- index persistent data --><a name="persistent-data"></a>
<p> A collection class is a container which holds a number of items in a
data structure and provides various operations to manipulate the
contents of the collection, such as insert item, remove item, find
item, etc.
<p> Qt has several value-based and several pointer-based collection
classes. The pointer-based collection classes work with pointers to
items, while the value-based classes store copies of their items. The
value-based collections are very similar to STL container classes, and
can be used with STL algorithms and containers. See the <a href="qt-template-lib.html">Qt Template Library</a> documentation for
details.
<p> The value-based collections are:
<ul>
<li> <a href="qvaluelist.html">QValueList</a>, a value-based list.
<li> <a href="qvaluevector.html">QValueVector</a>, a value-based vector.
<li> <a href="qvaluestack.html">QValueStack</a>, a value-based stack.
<li> <a href="qmap.html">QMap</a>, a value-based dictionary (associative array).
</ul>
<p> The pointer-based collections are:
<ul>
<li> <a href="qcache.html">QCache</a> and <a href="qintcache.html">QIntCache</a>, LRU (least recently used) caches.
<li> <a href="qdict.html">QDict</a>, <a href="qintdict.html">QIntDict</a> and <a href="qptrdict.html">QPtrDict</a> dictionaries.
<li> <a href="qptrlist.html">QPtrList</a>, a doubly linked list.
<li> <a href="qptrqueue.html">QPtrQueue</a>, a FIFO (first in, first out) queue.
<li> <a href="qptrstack.html">QPtrStack</a>, a LIFO (last in, first out) stack.
<li> <a href="qptrvector.html">QPtrVector</a>, a vector.
</ul>
<p> <a href="qmemarray.html">QMemArray</a> is exceptional; it is neither pointer nor value based,
but memory based. For maximum efficiency with the simple data types
usually used in arrays, it uses bitwise operations to copy and compare
array elements.
<p> Some of these classes have corresponding iterators. An iterator
is a class for traversing the items in a collection:
<ul>
<li> <a href="qcacheiterator.html">QCacheIterator</a> and
<a href="qintcacheiterator.html">QIntCacheIterator</a>
<li> <a href="qdictiterator.html">QDictIterator</a>,
<a href="qintdictiterator.html">QIntDictIterator</a>, and
<a href="qptrdictiterator.html">QPtrDictIterator</a>
<li> <a href="qptrlistiterator.html">QPtrListIterator</a>
<li> <a href="qvaluelistiterator.html">QValueListIterator</a>, and
<a href="qvaluelistconstiterator.html">QValueListConstIterator</a>
<li> <a href="qmapiterator.html">QMapIterator</a>, and
<a href="qmapconstiterator.html">QMapConstIterator</a>
</ul>
<p> The value-based collections plus algorithms operating on them are
grouped together in the <a href="qt-template-lib.html">Qt Template
Library</a>; see also the <a href="qtl.html">Qt Template
Library Classes</a>.
<p> The rest of this page dicusses the pointer-based containers.
<p> <h2> Architecture of the pointer-based containers
</h2>
<a name="1"></a><p> There are four internal base classes for the pointer-based
containers (QGCache, QGDict, QGList and QGVector) that operate on
void pointers. A thin template layer implements the actual
collections by casting item pointers to and from void pointers.
<p> This strategy allows Qt's templates to be very economical on space
(instantiating one of these templates adds only inlinable calls to
the base classes), without hurting performance.
<p> <h2> A <a href="qptrlist.html">QPtrList</a> Example
</h2>
<a name="2"></a><p> This example shows how to store Employee items in a list and prints
them out in reverse order:
<p> <pre>
#include <<a href="qptrlist-h.html">qptrlist.h</a>>
#include <<a href="qstring-h.html">qstring.h</a>>
#include <stdio.h>
class Employee
{
public:
Employee( const char *name, int salary ) { n=name; s=salary; }
const char *name() const { return n; }
int salary() const { return s; }
private:
<a href="qstring.html">QString</a> n;
int s;
};
int main()
{
<a href="qptrlist.html">QPtrList</a><Employee> list; // list of pointers to Employee
list.<a href="qptrcollection.html#setAutoDelete">setAutoDelete</a>( TRUE ); // delete items when they are removed
list.<a href="qptrlist.html#append">append</a>( new Employee("Bill", 50000) );
list.<a href="qptrlist.html#append">append</a>( new Employee("Steve",80000) );
list.<a href="qptrlist.html#append">append</a>( new Employee("Ron", 60000) );
<a href="qptrlistiterator.html">QPtrListIterator</a><Employee> it(list); // iterator for employee list
for ( it.<a href="qptrlistiterator.html#toLast">toLast</a>(); it.<a href="qptrlistiterator.html#current">current</a>(); --it) ) {
Employee *emp = it.<a href="qptrlistiterator.html#current">current</a>();
printf( "%s earns %d\n", emp->name(), emp->salary() );
}
return 0;
}
</pre>
<p> Program output:
<pre>
Ron earns 60000
Steve earns 80000
Bill earns 50000
</pre>
<p> <h2> Managing Collection Items
</h2>
<a name="3"></a><p> All pointer-based collections inherit the <a href="qptrcollection.html">QPtrCollection</a> base class.
This class only knows about the number of items in the collection and
the deletion strategy.
<p> By default, items in a collection are not deleted when they are
removed from the collection. The <a href="qptrcollection.html#setAutoDelete">QPtrCollection::setAutoDelete</a>()
function specifies the deletion strategy. In the list example, we
enable auto-deletion to make the list delete the items when they are
removed from the list.
<p> When inserting an item into a collection, only the pointer is copied,
not the item itself. This is called a <a href="shclass.html#shallow-copy">shallow copy</a>. It is possible to
make the collection copy all of the item's data (known as a <a href="shclass.html#deep-copy">deep copy</a>)
when an item is inserted. All collection functions that insert an
item call the virtual function <a href="qptrcollection.html#newItem">QPtrCollection::newItem</a>() for the item
to be inserted. Inherit a collection and reimplement it if you want
to have deep copies in your collection.
<p> When removing an item from a list, the virtual function
<a href="qptrcollection.html#deleteItem">QPtrCollection::deleteItem</a>() is called. The default implementation
in all collection classes deletes the item if auto-deletion is
enabled.
<p> <h2> Usage
</h2>
<a name="4"></a><p> A pointer-based collection class, such as <a href="qptrlist.html">QPtrList</a><type>, defines a
collection of <em>pointers</em> to <em>type</em> objects. The pointer (*) is
implicit.
<p> We discuss <a href="qptrlist.html">QPtrList</a> here, but the same techniques apply to all
pointer-based collection classes and all collection class iterators.
<p> Template instantiation:
<pre>
<a href="qptrlist.html">QPtrList</a><Employee> list; // wherever the list is used
</pre>
<p> The item's class or type, Employee in our example, must be defined prior
to the list definition.
<p> <pre>
// Does not work: Employee is not defined
class Employee;
<a href="qptrlist.html">QPtrList</a><Employee> list;
// This works: Employee is defined before it is used
class Employee {
...
};
<a href="qptrlist.html">QPtrList</a><Employee> list;
</pre>
<p> <h2> Iterators
</h2>
<a name="5"></a><p> Although <a href="qptrlist.html">QPtrList</a> has member functions to traverse the list, it can
often be better to make use of an iterator. <a href="qptrlistiterator.html">QPtrListIterator</a> is very
safe and can traverse lists that are being modified at the same time.
Multiple iterators can work independently on the same collection.
<p> A <a href="qptrlist.html">QPtrList</a> has an internal list of all the iterators that are
currently operating on it. When a list entry is removed, the list
updates all iterators accordingly.
<p> The <a href="qdict.html">QDict</a> and <a href="qcache.html">QCache</a> collections have no traversal functions. To
traverse these collections, you must use <a href="qdictiterator.html">QDictIterator</a> or <a href="qcacheiterator.html">QCacheIterator</a>.
<p> <h2> Predefined Collections
</h2>
<a name="6"></a><p> Qt has the following predefined collection classes:
<ul>
<li> String lists: <a href="qstrlist.html">QStrList</a>, <a href="qstrilist.html">QStrIList</a> (<a href="qstrlist-h.html">qstrlist.h</a>) and
<a href="qstringlist.html">QStringList</a> (<a href="qstringlist-h.html">qstringlist.h</a>)
<li> String vectors: QStrVec and QStrIVec (qstrvec.h); these are obsolete
</ul>
<p> In almost all cases you would choose <a href="qstringlist.html">QStringList</a>, a value
list of <a href="shclass.html#implicitly-shared">implicitly shared</a> <a href="qstring.html">QString</a> Unicode strings. QPtrStrList and
QPtrStrIList store only char pointers, not the strings themselves.
<p> <h2> List of Pointer-based Collection Classes and Related
Iterator Classes
</h2>
<a name="7"></a><p>
<p><table width="100%">
<tr bgcolor=#f0f0f0><td><b><a href="qasciicache.html">QAsciiCache</a></b><td>Template class that provides a cache based on char* keys
<tr bgcolor=#f0f0f0><td><b><a href="qasciicacheiterator.html">QAsciiCacheIterator</a></b><td>Iterator for QAsciiCache collections
<tr bgcolor=#f0f0f0><td><b><a href="qasciidict.html">QAsciiDict</a></b><td>Template class that provides a dictionary based on char* keys
<tr bgcolor=#f0f0f0><td><b><a href="qasciidictiterator.html">QAsciiDictIterator</a></b><td>Iterator for QAsciiDict collections
<tr bgcolor=#f0f0f0><td><b><a href="qbitarray.html">QBitArray</a></b><td>Array of bits
<tr bgcolor=#f0f0f0><td><b><a href="qbitval.html">QBitVal</a></b><td>Internal class, used with QBitArray
<tr bgcolor=#f0f0f0><td><b><a href="qbuffer.html">QBuffer</a></b><td>I/O device that operates on a QByteArray
<tr bgcolor=#f0f0f0><td><b><a href="qbytearray.html">QByteArray</a></b><td>Array of bytes
<tr bgcolor=#f0f0f0><td><b><a href="qcache.html">QCache</a></b><td>Template class that provides a cache based on QString keys
<tr bgcolor=#f0f0f0><td><b><a href="qcacheiterator.html">QCacheIterator</a></b><td>Iterator for QCache collections
<tr bgcolor=#f0f0f0><td><b><a href="qcstring.html">QCString</a></b><td>Abstraction of the classic C zero-terminated char array (char *)
<tr bgcolor=#f0f0f0><td><b><a href="qdict.html">QDict</a></b><td>Template class that provides a dictionary based on QString keys
<tr bgcolor=#f0f0f0><td><b><a href="qdictiterator.html">QDictIterator</a></b><td>Iterator for QDict collections
<tr bgcolor=#f0f0f0><td><b><a href="qintcache.html">QIntCache</a></b><td>Template class that provides a cache based on long keys
<tr bgcolor=#f0f0f0><td><b><a href="qintcacheiterator.html">QIntCacheIterator</a></b><td>Iterator for QIntCache collections
<tr bgcolor=#f0f0f0><td><b><a href="qintdict.html">QIntDict</a></b><td>Template class that provides a dictionary based on long keys
<tr bgcolor=#f0f0f0><td><b><a href="qintdictiterator.html">QIntDictIterator</a></b><td>Iterator for QIntDict collections
<tr bgcolor=#f0f0f0><td><b><a href="qobjectlist.html">QObjectList</a></b><td>QPtrList of QObjects
<tr bgcolor=#f0f0f0><td><b><a href="qobjectlistiterator.html">QObjectListIterator</a></b><td>Iterator for QObjectLists
<tr bgcolor=#f0f0f0><td><b><a href="qptrcollection.html">QPtrCollection</a></b><td>The base class of most pointer-based Qt collections
<tr bgcolor=#f0f0f0><td><b><a href="qptrdict.html">QPtrDict</a></b><td>Template class that provides a dictionary based on void* keys
<tr bgcolor=#f0f0f0><td><b><a href="qptrdictiterator.html">QPtrDictIterator</a></b><td>Iterator for QPtrDict collections
<tr bgcolor=#f0f0f0><td><b><a href="qptrlist.html">QPtrList</a></b><td>Template class that provides a list
<tr bgcolor=#f0f0f0><td><b><a href="qptrlistiterator.html">QPtrListIterator</a></b><td>Iterator for QPtrList collections
<tr bgcolor=#f0f0f0><td><b><a href="qptrqueue.html">QPtrQueue</a></b><td>Template class that provides a queue
<tr bgcolor=#f0f0f0><td><b><a href="qstrilist.html">QStrIList</a></b><td>Doubly-linked list of char* with case-insensitive comparison
<tr bgcolor=#f0f0f0><td><b><a href="qstrlist.html">QStrList</a></b><td>Doubly-linked list of char*
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