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251 lines
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<title>Collection Classes</title>
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<a href="index.html">
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<font color="#004faf">Home</font></a>
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<font color="#004faf">All Classes</font></a>
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<font color="#004faf">Main Classes</font></a>
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<font color="#004faf">Annotated</font></a>
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<font color="#004faf">Grouped Classes</font></a>
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<font color="#004faf">Functions</font></a>
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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>
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<p> <!-- index collection classes --><a name="collection-classes"></a><!-- index persistent data --><a name="persistent-data"></a>
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<p> A collection class is a container which holds a number of items in a
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data structure and provides various operations to manipulate the
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contents of the collection, such as insert item, remove item, find
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item, etc.
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<p> Qt has several value-based and several pointer-based collection
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classes. The pointer-based collection classes work with pointers to
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items, while the value-based classes store copies of their items. The
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value-based collections are very similar to STL container classes, and
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can be used with STL algorithms and containers. See the <a href="qt-template-lib.html">Qt Template Library</a> documentation for
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details.
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<p> The value-based collections are:
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<ul>
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<li> <a href="qvaluelist.html">QValueList</a>, a value-based list.
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<li> <a href="qvaluevector.html">QValueVector</a>, a value-based vector.
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<li> <a href="qvaluestack.html">QValueStack</a>, a value-based stack.
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<li> <a href="qmap.html">QMap</a>, a value-based dictionary (associative array).
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</ul>
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<p> The pointer-based collections are:
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<ul>
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<li> <a href="qcache.html">QCache</a> and <a href="qintcache.html">QIntCache</a>, LRU (least recently used) caches.
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<li> <a href="qdict.html">QDict</a>, <a href="qintdict.html">QIntDict</a> and <a href="qptrdict.html">QPtrDict</a> dictionaries.
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<li> <a href="qptrlist.html">QPtrList</a>, a doubly linked list.
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<li> <a href="qptrqueue.html">QPtrQueue</a>, a FIFO (first in, first out) queue.
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<li> <a href="qptrstack.html">QPtrStack</a>, a LIFO (last in, first out) stack.
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<li> <a href="qptrvector.html">QPtrVector</a>, a vector.
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</ul>
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<p> <a href="qmemarray.html">QMemArray</a> is exceptional; it is neither pointer nor value based,
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but memory based. For maximum efficiency with the simple data types
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usually used in arrays, it uses bitwise operations to copy and compare
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array elements.
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<p> Some of these classes have corresponding iterators. An iterator
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is a class for traversing the items in a collection:
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<ul>
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<li> <a href="qcacheiterator.html">QCacheIterator</a> and
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<a href="qintcacheiterator.html">QIntCacheIterator</a>
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<li> <a href="qdictiterator.html">QDictIterator</a>,
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<a href="qintdictiterator.html">QIntDictIterator</a>, and
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<a href="qptrdictiterator.html">QPtrDictIterator</a>
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<li> <a href="qptrlistiterator.html">QPtrListIterator</a>
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<li> <a href="qvaluelistiterator.html">QValueListIterator</a>, and
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<a href="qvaluelistconstiterator.html">QValueListConstIterator</a>
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<li> <a href="qmapiterator.html">QMapIterator</a>, and
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<a href="qmapconstiterator.html">QMapConstIterator</a>
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</ul>
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<p> The value-based collections plus algorithms operating on them are
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grouped together in the <a href="qt-template-lib.html">Qt Template
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Library</a>; see also the <a href="qtl.html">Qt Template
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Library Classes</a>.
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<p> The rest of this page dicusses the pointer-based containers.
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<p> <h2> Architecture of the pointer-based containers
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</h2>
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<a name="1"></a><p> There are four internal base classes for the pointer-based
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containers (QGCache, QGDict, QGList and QGVector) that operate on
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void pointers. A thin template layer implements the actual
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collections by casting item pointers to and from void pointers.
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<p> This strategy allows Qt's templates to be very economical on space
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(instantiating one of these templates adds only inlinable calls to
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the base classes), without hurting performance.
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<p> <h2> A <a href="qptrlist.html">QPtrList</a> Example
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</h2>
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<a name="2"></a><p> This example shows how to store Employee items in a list and prints
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them out in reverse order:
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<p> <pre>
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#include <<a href="qptrlist-h.html">qptrlist.h</a>>
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#include <<a href="qstring-h.html">qstring.h</a>>
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#include <stdio.h>
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class Employee
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{
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public:
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Employee( const char *name, int salary ) { n=name; s=salary; }
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const char *name() const { return n; }
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int salary() const { return s; }
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private:
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<a href="qstring.html">QString</a> n;
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int s;
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};
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int main()
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{
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<a href="qptrlist.html">QPtrList</a><Employee> list; // list of pointers to Employee
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list.<a href="qptrcollection.html#setAutoDelete">setAutoDelete</a>( TRUE ); // delete items when they are removed
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list.<a href="qptrlist.html#append">append</a>( new Employee("Bill", 50000) );
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list.<a href="qptrlist.html#append">append</a>( new Employee("Steve",80000) );
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list.<a href="qptrlist.html#append">append</a>( new Employee("Ron", 60000) );
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<a href="qptrlistiterator.html">QPtrListIterator</a><Employee> it(list); // iterator for employee list
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for ( it.<a href="qptrlistiterator.html#toLast">toLast</a>(); it.<a href="qptrlistiterator.html#current">current</a>(); --it) ) {
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Employee *emp = it.<a href="qptrlistiterator.html#current">current</a>();
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printf( "%s earns %d\n", emp->name(), emp->salary() );
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}
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return 0;
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}
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</pre>
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<p> Program output:
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<pre>
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Ron earns 60000
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Steve earns 80000
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Bill earns 50000
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</pre>
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<p> <h2> Managing Collection Items
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</h2>
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<a name="3"></a><p> All pointer-based collections inherit the <a href="qptrcollection.html">QPtrCollection</a> base class.
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This class only knows about the number of items in the collection and
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the deletion strategy.
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<p> By default, items in a collection are not deleted when they are
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removed from the collection. The <a href="qptrcollection.html#setAutoDelete">QPtrCollection::setAutoDelete</a>()
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function specifies the deletion strategy. In the list example, we
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enable auto-deletion to make the list delete the items when they are
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removed from the list.
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<p> When inserting an item into a collection, only the pointer is copied,
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not the item itself. This is called a <a href="shclass.html#shallow-copy">shallow copy</a>. It is possible to
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make the collection copy all of the item's data (known as a <a href="shclass.html#deep-copy">deep copy</a>)
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when an item is inserted. All collection functions that insert an
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item call the virtual function <a href="qptrcollection.html#newItem">QPtrCollection::newItem</a>() for the item
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to be inserted. Inherit a collection and reimplement it if you want
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to have deep copies in your collection.
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<p> When removing an item from a list, the virtual function
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<a href="qptrcollection.html#deleteItem">QPtrCollection::deleteItem</a>() is called. The default implementation
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in all collection classes deletes the item if auto-deletion is
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enabled.
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<p> <h2> Usage
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</h2>
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<a name="4"></a><p> A pointer-based collection class, such as <a href="qptrlist.html">QPtrList</a><type>, defines a
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collection of <em>pointers</em> to <em>type</em> objects. The pointer (*) is
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implicit.
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<p> We discuss <a href="qptrlist.html">QPtrList</a> here, but the same techniques apply to all
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pointer-based collection classes and all collection class iterators.
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<p> Template instantiation:
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<pre>
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<a href="qptrlist.html">QPtrList</a><Employee> list; // wherever the list is used
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</pre>
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<p> The item's class or type, Employee in our example, must be defined prior
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to the list definition.
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<p> <pre>
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// Does not work: Employee is not defined
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class Employee;
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<a href="qptrlist.html">QPtrList</a><Employee> list;
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// This works: Employee is defined before it is used
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class Employee {
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...
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};
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<a href="qptrlist.html">QPtrList</a><Employee> list;
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</pre>
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<p> <h2> Iterators
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</h2>
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<a name="5"></a><p> Although <a href="qptrlist.html">QPtrList</a> has member functions to traverse the list, it can
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often be better to make use of an iterator. <a href="qptrlistiterator.html">QPtrListIterator</a> is very
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safe and can traverse lists that are being modified at the same time.
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Multiple iterators can work independently on the same collection.
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<p> A <a href="qptrlist.html">QPtrList</a> has an internal list of all the iterators that are
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currently operating on it. When a list entry is removed, the list
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updates all iterators accordingly.
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<p> The <a href="qdict.html">QDict</a> and <a href="qcache.html">QCache</a> collections have no traversal functions. To
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traverse these collections, you must use <a href="qdictiterator.html">QDictIterator</a> or <a href="qcacheiterator.html">QCacheIterator</a>.
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<p> <h2> Predefined Collections
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</h2>
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<a name="6"></a><p> Qt has the following predefined collection classes:
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<ul>
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<li> String lists: <a href="qstrlist.html">QStrList</a>, <a href="qstrilist.html">QStrIList</a> (<a href="qstrlist-h.html">qstrlist.h</a>) and
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<a href="qstringlist.html">QStringList</a> (<a href="qstringlist-h.html">qstringlist.h</a>)
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<li> String vectors: QStrVec and QStrIVec (qstrvec.h); these are obsolete
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</ul>
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<p> In almost all cases you would choose <a href="qstringlist.html">QStringList</a>, a value
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list of <a href="shclass.html#implicitly-shared">implicitly shared</a> <a href="qstring.html">QString</a> Unicode strings. QPtrStrList and
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QPtrStrIList store only char pointers, not the strings themselves.
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<p> <h2> List of Pointer-based Collection Classes and Related
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Iterator Classes
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</h2>
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<a name="7"></a><p>
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<p><table width="100%">
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<tr bgcolor=#f0f0f0><td><b><a href="qasciicache.html">QAsciiCache</a></b><td>Template class that provides a cache based on char* keys
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<tr bgcolor=#f0f0f0><td><b><a href="qasciicacheiterator.html">QAsciiCacheIterator</a></b><td>Iterator for QAsciiCache collections
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<tr bgcolor=#f0f0f0><td><b><a href="qasciidict.html">QAsciiDict</a></b><td>Template class that provides a dictionary based on char* keys
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<tr bgcolor=#f0f0f0><td><b><a href="qasciidictiterator.html">QAsciiDictIterator</a></b><td>Iterator for QAsciiDict collections
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<tr bgcolor=#f0f0f0><td><b><a href="qbitarray.html">QBitArray</a></b><td>Array of bits
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<tr bgcolor=#f0f0f0><td><b><a href="qbitval.html">QBitVal</a></b><td>Internal class, used with QBitArray
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<tr bgcolor=#f0f0f0><td><b><a href="qbuffer.html">QBuffer</a></b><td>I/O device that operates on a QByteArray
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<tr bgcolor=#f0f0f0><td><b><a href="qbytearray.html">QByteArray</a></b><td>Array of bytes
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<tr bgcolor=#f0f0f0><td><b><a href="qcache.html">QCache</a></b><td>Template class that provides a cache based on QString keys
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<tr bgcolor=#f0f0f0><td><b><a href="qcacheiterator.html">QCacheIterator</a></b><td>Iterator for QCache collections
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<tr bgcolor=#f0f0f0><td><b><a href="qcstring.html">QCString</a></b><td>Abstraction of the classic C zero-terminated char array (char *)
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<tr bgcolor=#f0f0f0><td><b><a href="qdict.html">QDict</a></b><td>Template class that provides a dictionary based on QString keys
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<tr bgcolor=#f0f0f0><td><b><a href="qdictiterator.html">QDictIterator</a></b><td>Iterator for QDict collections
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<tr bgcolor=#f0f0f0><td><b><a href="qintcache.html">QIntCache</a></b><td>Template class that provides a cache based on long keys
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<tr bgcolor=#f0f0f0><td><b><a href="qintcacheiterator.html">QIntCacheIterator</a></b><td>Iterator for QIntCache collections
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<tr bgcolor=#f0f0f0><td><b><a href="qintdict.html">QIntDict</a></b><td>Template class that provides a dictionary based on long keys
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<tr bgcolor=#f0f0f0><td><b><a href="qintdictiterator.html">QIntDictIterator</a></b><td>Iterator for QIntDict collections
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<tr bgcolor=#f0f0f0><td><b><a href="qobjectlist.html">QObjectList</a></b><td>QPtrList of QObjects
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<tr bgcolor=#f0f0f0><td><b><a href="qobjectlistiterator.html">QObjectListIterator</a></b><td>Iterator for QObjectLists
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<tr bgcolor=#f0f0f0><td><b><a href="qptrcollection.html">QPtrCollection</a></b><td>The base class of most pointer-based Qt collections
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<tr bgcolor=#f0f0f0><td><b><a href="qptrdict.html">QPtrDict</a></b><td>Template class that provides a dictionary based on void* keys
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<tr bgcolor=#f0f0f0><td><b><a href="qptrdictiterator.html">QPtrDictIterator</a></b><td>Iterator for QPtrDict collections
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<tr bgcolor=#f0f0f0><td><b><a href="qptrlist.html">QPtrList</a></b><td>Template class that provides a list
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<tr bgcolor=#f0f0f0><td><b><a href="qptrlistiterator.html">QPtrListIterator</a></b><td>Iterator for QPtrList collections
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<tr bgcolor=#f0f0f0><td><b><a href="qptrqueue.html">QPtrQueue</a></b><td>Template class that provides a queue
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<tr bgcolor=#f0f0f0><td><b><a href="qstrilist.html">QStrIList</a></b><td>Doubly-linked list of char* with case-insensitive comparison
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<tr bgcolor=#f0f0f0><td><b><a href="qstrlist.html">QStrList</a></b><td>Doubly-linked list of char*
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</table>
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<p><address><hr><div align=center>
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<table width=100% cellspacing=0 border=0><tr>
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<td>Copyright © 2007
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<a href="troll.html">Trolltech</a><td align=center><a href="trademarks.html">Trademarks</a>
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<td align=right><div align=right>Qt 3.3.8</div>
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</table></div></address></body>
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