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321 lines
14 KiB
321 lines
14 KiB
14 years ago
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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
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<!-- /home/espenr/tmp/qt-3.3.8-espenr-2499/qt-x11-free-3.3.8/doc/qtl.doc:36 -->
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<html>
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<head>
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<meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1">
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<title>Qt Template Library</title>
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<style type="text/css"><!--
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fn { margin-left: 1cm; text-indent: -1cm; }
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a:link { color: #004faf; text-decoration: none }
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a:visited { color: #672967; text-decoration: none }
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body { background: #ffffff; color: black; }
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--></style>
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</head>
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<body>
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<table border="0" cellpadding="0" cellspacing="0" width="100%">
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<tr bgcolor="#E5E5E5">
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<td valign=center>
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<a href="index.html">
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<font color="#004faf">Home</font></a>
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| <a href="classes.html">
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<font color="#004faf">All Classes</font></a>
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| <a href="mainclasses.html">
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<font color="#004faf">Main Classes</font></a>
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| <a href="annotated.html">
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<font color="#004faf">Annotated</font></a>
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| <a href="groups.html">
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<font color="#004faf">Grouped Classes</font></a>
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| <a href="functions.html">
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<font color="#004faf">Functions</font></a>
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</td>
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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>Qt Template Library</h1>
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<p>
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<p> The Qt Template Library (QTL) is a set of templates that provide
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object containers. If a suitable STL implementation is not available
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on all your target platforms, the QTL can be used instead. It provides
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a list of objects, a vector (dynamic array) of objects, a map relating
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one type to another (also called a dictionary or associative array),
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and associated <a href="#Iterators">iterators</a> and <a href="#Algorithms">algorithms</a>. A container is an object which
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contains and manages other objects and provides iterators that allow
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the contained objects to be accessed.
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<p> The QTL classes' naming conventions are consistent with the other Qt
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classes (e.g., count(), isEmpty()). They also provide extra functions
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for compatibility with STL algorithms, such as size() and empty().
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Programmers already familiar with the STL <tt>map</tt> can use the
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STL-compatible functions if preferred.
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<p> Compared to the STL, the QTL only contains the most important features
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of the STL container API. Compared with the STL, QTL has no platform
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differences, but is often a little slower and often expands to less
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object code.
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<p> If you cannot make copies of the objects you want to store you should
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use <a href="qptrcollection.html">QPtrCollection</a> and friends, all of which operate on pointers
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rather than values. This applies, for example, to all classes derived
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from <a href="qobject.html">QObject</a>. A <a href="qobject.html">QObject</a> does not have a copy constructor, so using
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it as value is impossible. You may choose to store pointers to
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QObjects in a <a href="qvaluelist.html">QValueList</a>, but using <a href="qptrlist.html">QPtrList</a> directly seems to be the
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better choice for this kind of application domain. QPtrList, like all
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other QPtrCollection based containers, provides far more sanity
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checking than a speed-optimized value based container.
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<p> If you have objects that implement value semantics, and the STL is not
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available on your target platform, the Qt Template Library can be used
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instead. Value semantics require at least:
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<ul>
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<li> a copy constructor;
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<li> an assignment operator;
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<li> a defaultconstructor, i.e. a constructor that does not take any arguments.
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</ul>
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<p> Note that a fast copy constructor is absolutely crucial to achieve
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good overall performance of the container, since many copy operations
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will occur.
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<p> If you intend sorting your data you must implement <a href="qcstring.html#operator-lt-2">operator<</a>() for
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your data's class.
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<p> Good candidates for value based classes are <a href="qrect.html">QRect</a>, <a href="qpoint.html">QPoint</a>, <a href="qsize.html">QSize</a>,
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<a href="qstring.html">QString</a> and all simple C++ types, such as int, bool or double.
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<p> The Qt Template Library is designed for speed. Iterators are extremely
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fast. To achieve this performance, less error checking is done than in
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the <a href="qptrcollection.html">QPtrCollection</a> based containers. A QTL container, for example,
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does not track any associated iterators. This makes certain validity
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checks, for example when removing items, impossible to perform
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automatically, but does lead to extremely good performance.
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<p> <a name="Iterators"></a>
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<h2> Iterators
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</h2>
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<a name="1"></a><p> The Qt Template Library deals with value objects, not with pointers.
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For that reason, there is no other way of iterating over containers
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other than with iterators. This is no disadvantage as the size of an
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iterator matches the size of a normal pointer.
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<p> To iterate over a container, use a loop like this:
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<pre>
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typedef QValueList<int> List;
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List list;
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for( List::Iterator it = list.begin(); it != list.end(); ++it )
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printf( "Number is %i\n", *it );
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</pre>
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<p> begin() returns the iterator pointing at the first element, while
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end() returns an iterator that points <em>after</em> the last element. end()
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marks an invalid position, so it can never be dereferenced. It's the
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break condition in any iteration, whether the start point is from
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begin() or fromLast(). For maximum speed, use increment or decrement
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iterators with the prefix operator (++it, --it) instead of the postfix
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operator (it++, it--), since the former is slightly faster.
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<p> The same concept applies to the other container classes:
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<pre>
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typedef QMap<QString,QString> Map;
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Map map;
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for( Map::iterator it = map.begin(); it != map.end(); ++it )
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printf( "Key=%s Data=%s\n", it.key().ascii(), it.data().ascii() );
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typedef QValueVector<int> Vector;
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Vector vec;
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for( Vector::iterator it = vec.begin(); it != vec.end(); ++it )
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printf( "Data=%d\n", *it );
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</pre>
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<p> There are two kind of iterators, the volatile iterator shown in the
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examples above and a version that returns a const reference to its
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current object, the ConstIterator. Const iterators are required
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whenever the container itself is const, such as a member variable
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inside a const function. Assigning a ConstIterator to a normal
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Iterator is not allowed as it would violate const semantics.
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<p> <a name="Algorithms"></a>
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<h2> Algorithms
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</h2>
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<a name="2"></a><p> The Qt Template Library defines a number of algorithms that operate on
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its containers. These algorithms are implemented as template functions
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and provide useful generic code which can be applied to any container
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that provides iterators (including your own containers).
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<p> <h3> qHeapSort()
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</h3>
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<a name="2-1"></a><p> qHeapSort() provides a well known sorting algorithm. You can use it
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like this:
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<pre>
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typedef QValueList<int> List;
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List list;
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list << 42 << 100 << 1234 << 12 << 8;
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qHeapSort( list );
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List list2;
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list2 << 42 << 100 << 1234 << 12 << 8;
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List::Iterator b = list2.find( 100 );
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List::Iterator e = list2.find( 8 );
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qHeapSort( b, e );
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double arr[] = { 3.2, 5.6, 8.9 };
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qHeapSort( arr, arr + 3 );
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</pre>
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<p> The first example sorts the entire list. The second example sorts only
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those elements that fall between the two iterators, i.e. 100, 1234 and
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12. The third example shows that iterators act like pointers and can
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be treated as such.
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<p> If using your own data types you must implement <a href="qcstring.html#operator-lt-2">operator<</a>() for
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your data's class.
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<p> Naturally, the sorting templates won't work with const iterators.
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<p> <a name="qSwap"></a>
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<h3> qSwap()
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</h3>
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<a name="2-2"></a><p> qSwap() exchanges the values of two variables:
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<pre>
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<a href="qstring.html">QString</a> second( "Einstein" );
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<a href="qstring.html">QString</a> name( "Albert" );
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qSwap( second, name );
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</pre>
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<p> <a name="qCount"></a>
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<h3> qCount()
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</h3>
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<a name="2-3"></a><p> The qCount() template function counts the number of occurrences of a
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value within a container. For example:
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<pre>
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<a href="qvaluelist.html">QValueList</a><int> list;
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list.<a href="qvaluelist.html#push_back">push_back</a>( 1 );
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list.<a href="qvaluelist.html#push_back">push_back</a>( 1 );
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list.<a href="qvaluelist.html#push_back">push_back</a>( 1 );
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list.<a href="qvaluelist.html#push_back">push_back</a>( 2 );
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int c = 0;
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qCount( list.<a href="qvaluelist.html#begin">begin</a>(), list.<a href="qvaluelist.html#end">end</a>(), 1, c ); // c == 3
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</pre>
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<p> <a name="qFind"></a>
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<h3> qFind()
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</h3>
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<a name="2-4"></a><p> The qFind() template function finds the first occurrence of a value
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within a container. For example:
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<pre>
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<a href="qvaluelist.html">QValueList</a><int> list;
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list.<a href="qvaluelist.html#push_back">push_back</a>( 1 );
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list.<a href="qvaluelist.html#push_back">push_back</a>( 1 );
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list.<a href="qvaluelist.html#push_back">push_back</a>( 1 );
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list.<a href="qvaluelist.html#push_back">push_back</a>( 2 );
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<a href="qvaluelistiterator.html">QValueListIterator</a><int> it = qFind( list.<a href="qvaluelist.html#begin">begin</a>(), list.<a href="qvaluelist.html#end">end</a>(), 2 );
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</pre>
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<p> <a name="qFill"></a>
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<h3> qFill()
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</h3>
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<a name="2-5"></a><p> The qFill() template function fills a range with copies of a value.
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For example:
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<pre>
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<a href="qvaluevector.html">QValueVector</a><int> vec(3);
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qFill( vec.<a href="qvaluevector.html#begin">begin</a>(), vec.<a href="qvaluevector.html#end">end</a>(), 99 ); // vec contains 99, 99, 99
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</pre>
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<p> <a name="qEqual"></a>
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<h3> qEqual()
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</h3>
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<a name="2-6"></a><p> The qEqual() template function compares two ranges for equality of
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their elements. Note that the number of elements in each range is not
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considered, only if the elements in the first range are equal to the
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corresponding elements in the second range (consequently, both ranges
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must be valid). For example:
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<pre>
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<a href="qvaluevector.html">QValueVector</a><int> v1(3);
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v1[0] = 1;
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v1[2] = 2;
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v1[3] = 3;
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<a href="qvaluevector.html">QValueVector</a><int> v2(5);
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v2[0] = 1;
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v2[2] = 2;
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v2[3] = 3;
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v2[4] = 4;
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v2[5] = 5;
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bool b = qEqual( v1.<a href="qvaluevector.html#begin">begin</a>(), v2.<a href="qvaluevector.html#end">end</a>(), v2.<a href="qvaluevector.html#begin">begin</a>() );
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// b == TRUE
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</pre>
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<p> <a name="qCopy"></a>
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<h3> qCopy()
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</h3>
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<a name="2-7"></a><p> The qCopy() template function copies a range of elements to an
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OutputIterator, in this case a QTextOStreamIterator:
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<pre>
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<a href="qvaluelist.html">QValueList</a><int> list;
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list.<a href="qvaluelist.html#push_back">push_back</a>( 100 );
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list.<a href="qvaluelist.html#push_back">push_back</a>( 200 );
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list.<a href="qvaluelist.html#push_back">push_back</a>( 300 );
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<a href="qtextostream.html">QTextOStream</a> str( stdout );
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qCopy( list.<a href="qvaluelist.html#begin">begin</a>(), list.<a href="qvaluelist.html#end">end</a>(), QTextOStreamIterator(str) );
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</pre>
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<p>
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<p> <a name="qCopyBackward"></a>
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<h3> qCopyBackward()
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</h3>
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<a name="2-8"></a><p> The qCopyBackward() template function copies a container or a slice of
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a container to an OutputIterator, but in reverse order, for example:
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<pre>
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<a href="qvaluevector.html">QValueVector</a><int> vec(3);
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vec.<a href="qvaluevector.html#push_back">push_back</a>( 100 );
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vec.<a href="qvaluevector.html#push_back">push_back</a>( 200 );
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vec.<a href="qvaluevector.html#push_back">push_back</a>( 300 );
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<a href="qvaluevector.html">QValueVector</a><int> another;
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qCopyBackward( vec.<a href="qvaluevector.html#begin">begin</a>(), vec.<a href="qvaluevector.html#end">end</a>(), another.<a href="qvaluevector.html#begin">begin</a>() );
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// 'another' now contains 100, 200, 300
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// however the elements are copied one at a time
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// in reverse order (300, 200, then 100)
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</pre>
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<p> <h3> QTL Iterators
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</h3>
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<a name="2-9"></a><p> You can use any Qt Template Library iterator as the OutputIterator.
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Just make sure that the right hand of the iterator has as many
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elements present as you want to insert. The following example
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illustrates this:
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<p> <pre>
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<a href="qstringlist.html">QStringList</a> list1, list2;
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list1 << "Weis" << "Ettrich" << "Arnt" << "Sue";
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list2 << "Torben" << "Matthias";
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qCopy( list2.begin(), list2.end(), list1.<a href="qvaluelist.html#begin">begin</a>() );
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<a href="qvaluevector.html">QValueVector</a><QString> vec( list1.<a href="qvaluelist.html#size">size</a>(), "Dave" );
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qCopy( list2.begin(), list2.end(), vec.<a href="qvaluevector.html#begin">begin</a>() );
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</pre>
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<p> At the end of this code fragment, the list list1 contains "Torben",
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"Matthias", "Arnt" and "Sue", with the prior contents being
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overwritten. The vector vec contains "Torben", "Matthias", "Dave" and
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"Dave", also with the prior contents being overwritten.
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<p> If you write new algorithms, consider writing them as template
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functions in order to make them usable with as many containers
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as possible. In the above example, you could just as easily print out
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a standard C++ array with qCopy():
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<p> <pre>
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int arr[] = { 100, 200, 300 };
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<a href="qtextostream.html">QTextOStream</a> str( stdout );
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qCopy( arr, arr + 3, QTextOStreamIterator( str ) );
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</pre>
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<p> <h2> Streaming
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</h2>
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<a name="3"></a><p> All the containers we've mentioned can be serialized with the
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appropriate streaming operators. Here is an example.
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<p> <pre>
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<a href="qdatastream.html">QDataStream</a> str(...);
|
||
|
|
<a href="qvaluelist.html">QValueList</a><QRect> list;
|
||
|
|
// ... fill the list here
|
||
|
|
str << list;
|
||
|
|
</pre>
|
||
|
|
|
||
|
|
<p> The container can be read in again with:
|
||
|
|
<p> <pre>
|
||
|
|
<a href="qvaluelist.html">QValueList</a><QRect> list;
|
||
|
|
str >> list;
|
||
|
|
</pre>
|
||
|
|
|
||
|
|
<p> The same applies to <a href="qstringlist.html">QStringList</a>, <a href="qvaluestack.html">QValueStack</a> and <a href="qmap.html">QMap</a>.
|
||
|
|
|
||
|
|
<!-- 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>Qt 3.3.8</div>
|
||
|
|
</table></div></address></body>
|
||
|
|
</html>
|