<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN"> <!-- /home/espenr/tmp/qt-3.3.8-espenr-2499/qt-x11-free-3.3.8/doc/collect.doc:36 --> <html> <head> <meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1"> <title>Collection Classes</title> <style type="text/css"><!-- fn { margin-left: 1cm; text-indent: -1cm; } a:link { color: #004faf; text-decoration: none } a:visited { color: #672967; text-decoration: none } body { background: #ffffff; color: black; } --></style> </head> <body> <table border="0" cellpadding="0" cellspacing="0" width="100%"> <tr bgcolor="#E5E5E5"> <td valign=center> <a href="index.html"> <font color="#004faf">Home</font></a> | <a href="classes.html"> <font color="#004faf">All Classes</font></a> | <a href="mainclasses.html"> <font color="#004faf">Main Classes</font></a> | <a href="annotated.html"> <font color="#004faf">Annotated</font></a> | <a href="groups.html"> <font color="#004faf">Grouped Classes</font></a> | <a href="functions.html"> <font color="#004faf">Functions</font></a> </td> <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="ntqvaluelist.html">TQValueList</a>, a value-based list. <li> <a href="ntqvaluevector.html">TQValueVector</a>, a value-based vector. <li> <a href="ntqvaluestack.html">TQValueStack</a>, a value-based stack. <li> <a href="ntqmap.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="ntqptrdict.html">TQPtrDict</a> dictionaries. <li> <a href="ntqptrlist.html">TQPtrList</a>, a doubly linked list. <li> <a href="ntqptrqueue.html">TQPtrQueue</a>, a FIFO (first in, first out) queue. <li> <a href="ntqptrstack.html">TQPtrStack</a>, a LIFO (last in, first out) stack. <li> <a href="ntqptrvector.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="qptrdictiterator.html">TQPtrDictIterator</a> <li> <a href="qptrlistiterator.html">TQPtrListIterator</a> <li> <a href="qvaluelistiterator.html">TQValueListIterator</a>, and <a href="qvaluelistconstiterator.html">TQValueListConstIterator</a> <li> <a href="qmapiterator.html">TQMapIterator</a>, and <a href="qmapconstiterator.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="ntqptrlist.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 <<a href="qptrlist-h.html">ntqptrlist.h</a>> #include <<a href="qstring-h.html">ntqstring.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="ntqstring.html">TQString</a> n; int s; }; int main() { <a href="ntqptrlist.html">TQPtrList</a><Employee> list; // list of pointers to Employee list.<a href="ntqptrcollection.html#setAutoDelete">setAutoDelete</a>( TRUE ); // delete items when they are removed list.<a href="ntqptrlist.html#append">append</a>( new Employee("Bill", 50000) ); list.<a href="ntqptrlist.html#append">append</a>( new Employee("Steve",80000) ); list.<a href="ntqptrlist.html#append">append</a>( new Employee("Ron", 60000) ); <a href="qptrlistiterator.html">TQPtrListIterator</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="ntqptrcollection.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="ntqptrcollection.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="ntqptrcollection.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="ntqptrcollection.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="ntqptrlist.html">TQPtrList</a><type>, defines a collection of <em>pointers</em> to <em>type</em> objects. The pointer (*) is implicit. <p> We discuss <a href="ntqptrlist.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="ntqptrlist.html">TQPtrList</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="ntqptrlist.html">TQPtrList</a><Employee> list; // This works: Employee is defined before it is used class Employee { ... }; <a href="ntqptrlist.html">TQPtrList</a><Employee> list; </pre> <p> <h2> Iterators </h2> <a name="5"></a><p> Although <a href="ntqptrlist.html">TQPtrList</a> has member functions to traverse the list, it can often be better to make use of an iterator. <a href="qptrlistiterator.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="ntqptrlist.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="ntqobjectlist.html">TQObjectList</a></b><td>TQPtrList of TQObjects <tr bgcolor=#f0f0f0><td><b><a href="qobjectlistiterator.html">TQObjectListIterator</a></b><td>Iterator for TQObjectLists <tr bgcolor=#f0f0f0><td><b><a href="ntqptrcollection.html">TQPtrCollection</a></b><td>The base class of most pointer-based TQt collections <tr bgcolor=#f0f0f0><td><b><a href="ntqptrdict.html">TQPtrDict</a></b><td>Template class that provides a dictionary based on void* keys <tr bgcolor=#f0f0f0><td><b><a href="qptrdictiterator.html">TQPtrDictIterator</a></b><td>Iterator for TQPtrDict collections <tr bgcolor=#f0f0f0><td><b><a href="ntqptrlist.html">TQPtrList</a></b><td>Template class that provides a list <tr bgcolor=#f0f0f0><td><b><a href="qptrlistiterator.html">TQPtrListIterator</a></b><td>Iterator for TQPtrList collections <tr bgcolor=#f0f0f0><td><b><a href="ntqptrqueue.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* </table> <!-- eof --> <p><address><hr><div align=center> <table width=100% cellspacing=0 border=0><tr> <td>Copyright © 2007 <a href="troll.html">Trolltech</a><td align=center><a href="trademarks.html">Trademarks</a> <td align=right><div align=right>TQt 3.3.8</div> </table></div></address></body> </html>