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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> TQt 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">TQt Template Library</a> documentation for
details.
<p> The value-based collections are:
<ul>
<li> <a href="tqvaluelist.html">TQValueList</a>, a value-based list.
<li> <a href="tqvaluevector.html">TQValueVector</a>, a value-based vector.
<li> <a href="tqvaluestack.html">TQValueStack</a>, a value-based stack.
<li> <a href="tqmap.html">TQMap</a>, a value-based dictionary (associative array).
</ul>
<p> The pointer-based collections are:
<ul>
<li> <a href="ntqcache.html">TQCache</a> and <a href="ntqintcache.html">TQIntCache</a>, LRU (least recently used) caches.
<li> <a href="ntqdict.html">TQDict</a>, <a href="ntqintdict.html">TQIntDict</a> and <a href="tqptrdict.html">TQPtrDict</a> dictionaries.
<li> <a href="tqptrlist.html">TQPtrList</a>, a doubly linked list.
<li> <a href="tqptrqueue.html">TQPtrQueue</a>, a FIFO (first in, first out) queue.
<li> <a href="tqptrstack.html">TQPtrStack</a>, a LIFO (last in, first out) stack.
<li> <a href="tqptrvector.html">TQPtrVector</a>, a vector.
</ul>
<p> <a href="ntqmemarray.html">TQMemArray</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">TQCacheIterator</a> and
<a href="qintcacheiterator.html">TQIntCacheIterator</a>
<li> <a href="qdictiterator.html">TQDictIterator</a>,
<a href="qintdictiterator.html">TQIntDictIterator</a>, and
<a href="tqptrdictiterator.html">TQPtrDictIterator</a>
<li> <a href="tqptrlistiterator.html">TQPtrListIterator</a>
<li> <a href="tqvaluelistiterator.html">TQValueListIterator</a>, and
<a href="tqvaluelistconstiterator.html">TQValueListConstIterator</a>
<li> <a href="tqmapiterator.html">TQMapIterator</a>, and
<a href="tqmapconstiterator.html">TQMapConstIterator</a>
</ul>
<p> The value-based collections plus algorithms operating on them are
grouped together in the <a href="qt-template-lib.html">TQt Template
Library</a>; see also the <a href="ntqtl.html">TQt 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 (TQGCache, TQGDict, TQGList and TQGVector) 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 TQt'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="tqptrlist.html">TQPtrList</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 &lt;<a href="tqptrlist-h.html">tqptrlist.h</a>&gt;
    #include &lt;<a href="qstring-h.html">ntqstring.h</a>&gt;
    #include &lt;stdio.h&gt;

    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="ntqstring.html">TQString</a>     n;
        int         s;
    };

    int main()
    {
        <a href="tqptrlist.html">TQPtrList</a>&lt;Employee&gt; list;        // list of pointers to Employee
        list.<a href="tqptrcollection.html#setAutoDelete">setAutoDelete</a>( TRUE );     // delete items when they are removed

        list.<a href="tqptrlist.html#append">append</a>( new Employee("Bill", 50000) );
        list.<a href="tqptrlist.html#append">append</a>( new Employee("Steve",80000) );
        list.<a href="tqptrlist.html#append">append</a>( new Employee("Ron",  60000) );

        <a href="tqptrlistiterator.html">TQPtrListIterator</a>&lt;Employee&gt; it(list); // iterator for employee list
        for ( it.<a href="tqptrlistiterator.html#toLast">toLast</a>(); it.<a href="tqptrlistiterator.html#current">current</a>(); --it) ) {
            Employee *emp = it.<a href="tqptrlistiterator.html#current">current</a>();
            printf( "%s earns %d\n", emp-&gt;name(), emp-&gt;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="tqptrcollection.html">TQPtrCollection</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="tqptrcollection.html#setAutoDelete">TQPtrCollection::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="tqptrcollection.html#newItem">TQPtrCollection::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="tqptrcollection.html#deleteItem">TQPtrCollection::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="tqptrlist.html">TQPtrList</a>&lt;type&gt;, defines a
collection of <em>pointers</em> to <em>type</em> objects. The pointer (*) is
implicit.
<p> We discuss <a href="tqptrlist.html">TQPtrList</a> here, but the same techniques apply to all
pointer-based collection classes and all collection class iterators.
<p> Template instantiation:
<pre>
    <a href="tqptrlist.html">TQPtrList</a>&lt;Employee&gt; 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="tqptrlist.html">TQPtrList</a>&lt;Employee&gt; list;

    // This works: Employee is defined before it is used
    class Employee {
        ...
    };
    <a href="tqptrlist.html">TQPtrList</a>&lt;Employee&gt; list;
</pre>
 
<p> <h2> Iterators
</h2>
<a name="5"></a><p> Although <a href="tqptrlist.html">TQPtrList</a> has member functions to traverse the list, it can
often be better to make use of an iterator. <a href="tqptrlistiterator.html">TQPtrListIterator</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="tqptrlist.html">TQPtrList</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="ntqdict.html">TQDict</a> and <a href="ntqcache.html">TQCache</a> collections have no traversal functions. To
traverse these collections, you must use <a href="qdictiterator.html">TQDictIterator</a> or <a href="qcacheiterator.html">TQCacheIterator</a>.
<p> <h2> Predefined Collections
</h2>
<a name="6"></a><p> TQt has the following predefined collection classes:
<ul>
<li> String lists: <a href="ntqstrlist.html">TQStrList</a>, <a href="qstrilist.html">TQStrIList</a> (<a href="qstrlist-h.html">ntqstrlist.h</a>) and
<a href="ntqstringlist.html">TQStringList</a> (<a href="qstringlist-h.html">ntqstringlist.h</a>)
<li> String vectors: TQStrVec and TQStrIVec (ntqstrvec.h); these are obsolete
</ul>
<p> In almost all cases you would choose <a href="ntqstringlist.html">TQStringList</a>, a value
list of <a href="shclass.html#implicitly-shared">implicitly shared</a> <a href="ntqstring.html">TQString</a> Unicode strings. TQPtrStrList and
TQPtrStrIList 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="ntqasciicache.html">TQAsciiCache</a></b><td>Template class that provides a cache based on char* keys
<tr bgcolor=#f0f0f0><td><b><a href="qasciicacheiterator.html">TQAsciiCacheIterator</a></b><td>Iterator for TQAsciiCache collections
<tr bgcolor=#f0f0f0><td><b><a href="ntqasciidict.html">TQAsciiDict</a></b><td>Template class that provides a dictionary based on char* keys
<tr bgcolor=#f0f0f0><td><b><a href="qasciidictiterator.html">TQAsciiDictIterator</a></b><td>Iterator for TQAsciiDict collections
<tr bgcolor=#f0f0f0><td><b><a href="ntqbitarray.html">TQBitArray</a></b><td>Array of bits
<tr bgcolor=#f0f0f0><td><b><a href="qbitval.html">TQBitVal</a></b><td>Internal class, used with TQBitArray
<tr bgcolor=#f0f0f0><td><b><a href="ntqbuffer.html">TQBuffer</a></b><td>I/O device that operates on a TQByteArray
<tr bgcolor=#f0f0f0><td><b><a href="qbytearray.html">TQByteArray</a></b><td>Array of bytes
<tr bgcolor=#f0f0f0><td><b><a href="ntqcache.html">TQCache</a></b><td>Template class that provides a cache based on TQString keys
<tr bgcolor=#f0f0f0><td><b><a href="qcacheiterator.html">TQCacheIterator</a></b><td>Iterator for TQCache collections
<tr bgcolor=#f0f0f0><td><b><a href="ntqcstring.html">TQCString</a></b><td>Abstraction of the classic C zero-terminated char array (char *)
<tr bgcolor=#f0f0f0><td><b><a href="ntqdict.html">TQDict</a></b><td>Template class that provides a dictionary based on TQString keys
<tr bgcolor=#f0f0f0><td><b><a href="qdictiterator.html">TQDictIterator</a></b><td>Iterator for TQDict collections
<tr bgcolor=#f0f0f0><td><b><a href="ntqintcache.html">TQIntCache</a></b><td>Template class that provides a cache based on long keys
<tr bgcolor=#f0f0f0><td><b><a href="qintcacheiterator.html">TQIntCacheIterator</a></b><td>Iterator for TQIntCache collections
<tr bgcolor=#f0f0f0><td><b><a href="ntqintdict.html">TQIntDict</a></b><td>Template class that provides a dictionary based on long keys
<tr bgcolor=#f0f0f0><td><b><a href="qintdictiterator.html">TQIntDictIterator</a></b><td>Iterator for TQIntDict collections
<tr bgcolor=#f0f0f0><td><b><a href="tqobjectlist.html">TQObjectList</a></b><td>TQPtrList of TQObjects
<tr bgcolor=#f0f0f0><td><b><a href="tqobjectlistiterator.html">TQObjectListIterator</a></b><td>Iterator for TQObjectLists
<tr bgcolor=#f0f0f0><td><b><a href="tqptrcollection.html">TQPtrCollection</a></b><td>The base class of most pointer-based TQt collections
<tr bgcolor=#f0f0f0><td><b><a href="tqptrdict.html">TQPtrDict</a></b><td>Template class that provides a dictionary based on void* keys
<tr bgcolor=#f0f0f0><td><b><a href="tqptrdictiterator.html">TQPtrDictIterator</a></b><td>Iterator for TQPtrDict collections
<tr bgcolor=#f0f0f0><td><b><a href="tqptrlist.html">TQPtrList</a></b><td>Template class that provides a list
<tr bgcolor=#f0f0f0><td><b><a href="tqptrlistiterator.html">TQPtrListIterator</a></b><td>Iterator for TQPtrList collections
<tr bgcolor=#f0f0f0><td><b><a href="tqptrqueue.html">TQPtrQueue</a></b><td>Template class that provides a queue
<tr bgcolor=#f0f0f0><td><b><a href="qstrilist.html">TQStrIList</a></b><td>Doubly-linked list of char* with case-insensitive comparison
<tr bgcolor=#f0f0f0><td><b><a href="ntqstrlist.html">TQStrList</a></b><td>Doubly-linked list of char*
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