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/****************************************************************************
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**
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** Copyright (C) 2009 Nokia Corporation and/or its subsidiary(-ies).
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** All rights reserved.
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** Contact: Nokia Corporation (qt-info@nokia.com)
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**
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** This file is part of the documentation of the Qt Toolkit.
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**
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** $QT_BEGIN_LICENSE:LGPL$
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** No Commercial Usage
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** This file contains pre-release code and may not be distributed.
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** contained in the Technology Preview License Agreement accompanying
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** this package.
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**
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** GNU Lesser General Public License Usage
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** In addition, as a special exception, Nokia gives you certain additional
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** rights. These rights are described in the Nokia Qt LGPL Exception
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** version 1.1, included in the file LGPL_EXCEPTION.txt in this package.
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**
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**
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**
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**
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**
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**
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** $QT_END_LICENSE$
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**
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****************************************************************************/
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/*!
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\page qt4-tulip.html
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\title The Tulip Container Classes
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\contentspage {What's New in Qt 4}{Home}
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\previouspage What's New in Qt 4
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\nextpage The Interview Framework
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Qt 4 introduces a new set of containers that supersede both the old
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QCollection pointer-based containers and the newer QTL value-based
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containers.
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\tableofcontents
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\section1 General Overview
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The Tulip containers are similar to Qt 3's QTL containers
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(QValueList, QValueVector, QMap), but have the following
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advantages:
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\list
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\o The containers provide new iterators with a nicer, less
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error-prone syntax than STL, inspired by Java's iterators. (The
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STL-style iterators are still available as a lightweight,
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STL-compatible alternative.)
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\o The containers have been optimized for minimal code expansion.
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\o An empty container performs no memory allocation, and only
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requires the same space as a pointer.
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\o Even though they are implicitly shared, they can safely be copied
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across different threads without formality. There's no need to use
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\c QDeepCopy.
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\endlist
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Tulip provides the following sequential containers: QList,
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QLinkedList, QVector, QStack, and QQueue. For most
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applications, QList is the best type to use. Although it is
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implemented as an array-list, it provides very fast prepends and
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appends. If you really need a linked-list, use QLinkedList; if you
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want your items to occupy consecutive memory locations, use QVector.
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QStack and QQueue are convenience classes that provide LIFO and
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FIFO semantics.
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Tulip also provides these associative containers: QMap,
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QMultiMap, QHash, QMultiHash, and QSet. The "Multi" containers
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conveniently support multiple values associated with a single
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key. The "Hash" containers provide faster lookup by using a hash
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function instead of a binary search on a sorted set.
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The Tulip containers support the \l foreach keyword, a Qt-specific
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addition to the C++ language that is implemented using the standard
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C++ preprocessor. The syntax is:
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\snippet doc/src/snippets/code/doc_src_qt4-tulip.qdoc 0
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Example:
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\snippet doc/src/snippets/code/doc_src_qt4-tulip.qdoc 1
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The iterator variable can also be defined outside the loop. For
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example:
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\snippet doc/src/snippets/code/doc_src_qt4-tulip.qdoc 2
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Just like standard \c for loops, foreach supports braces, \c
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break, \c continue, and nested loops. Qt makes a copy of the
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container when it enters the loop. If you modify the container as
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you are iterating, that won't affect the loop.
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For details about the new containers, see the
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\l{Generic Containers} and \l{Generic Algorithms} overview documents.
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In addition to the new containers, considerable work has also gone into
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QByteArray and QString. The Qt 3 QCString class has been
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merged with QByteArray. The new QByteArray automatically provides
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a '\0' terminator after the last character. For example, the byte array
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of size 5 containing "abcde" has a null byte at position 5 (one past
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the end). This solves all the typical problems that occurred in Qt 3
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with conversions between QByteArray and QCString.
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To avoid crashes, QByteArray::data() never returns a null
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pointer. Furthermore, the distinction between null and empty
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strings has been watered down so that \c{QByteArray() ==
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QByteArray("")} and \c{QString() == QString("")}.
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\section1 Examples
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The first group of examples show how to use the new Java-style
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iterators. The main difference between the Java-style iterators and the
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STL-style iterators is that the Java-style ones point between items (or
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before the first item, or after the last item), whereas the STL ones
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point at an item (or past the last item). One advantage of the
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Java-style iterators is that iterating forward and backward are
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symmetric operations.
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Traversing a container using a Java-style iterator:
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\snippet doc/src/snippets/code/doc_src_qt4-tulip.qdoc 3
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Modifying items using a Java-style iterator:
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\snippet doc/src/snippets/code/doc_src_qt4-tulip.qdoc 4
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Removing items using a Java-style iterator:
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\snippet doc/src/snippets/code/doc_src_qt4-tulip.qdoc 5
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Iterating over items with a particular value using STL-style vs.
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Java-style iterators:
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\snippet doc/src/snippets/code/doc_src_qt4-tulip.qdoc 6
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Modifying and removing items using STL-style vs. Java-style
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iterators:
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\snippet doc/src/snippets/code/doc_src_qt4-tulip.qdoc 7
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The next group of examples show the API of the container classes
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themselves. The API is similar to the QTL classes of Qt 3, but is nicer
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in many respects.
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Iterating over a QList using an index (which is fast even for large
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lists, because QList is implemented as an array-list):
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\snippet doc/src/snippets/code/doc_src_qt4-tulip.qdoc 8
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Retrieving a value from a map, using a default value if the key
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doesn't exist:
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\snippet doc/src/snippets/code/doc_src_qt4-tulip.qdoc 9
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Getting all the values for a particular key in a QMultiMap or QMultiHash:
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\snippet doc/src/snippets/code/doc_src_qt4-tulip.qdoc 10
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\section1 Comparison with Qt 3
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Tulip containers are value based. If you want to store a list where
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each item is a QWidget *, use QList<QWidget *>.
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The new containers do not support auto-delete. In practice, we
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discovered that the only case where auto-delete proved worthwhile was
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when the data really should be stored as a value rather than as a
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pointer (e.g., QList<int> rather than QList<int *>). If you need
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to delete all the items in a container, use qDeleteAll().
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If you use QValueList in Qt 3, you can replace it with either
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QList or QLinkedList in Qt 4. In most cases, QList is the best
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choice: It is typically faster, results in less code in your
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executable, and requires less memory. However, QLinkedList's
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iterators provide stronger guarantees, and only QLinkedList provides
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constant-time insertions in the middle, which can make a difference for
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lists with thousands of items.
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If you use QValueVector or QMap in Qt 3, the corresponding Qt 4
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classes (QVector, QMap) are very similar to use.
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*/
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