/**************************************************************************** ** ** QValueVector class documentation ** ** Copyright (C) 1992-2008 Trolltech ASA. 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Licensees holding valid Qt ** Commercial licenses may use this file in accordance with the Qt ** Commercial License Agreement provided with the Software. ** ** This file is provided "AS IS" with NO WARRANTY OF ANY KIND, ** INCLUDING THE WARRANTIES OF DESIGN, MERCHANTABILITY AND FITNESS FOR ** A PARTICULAR PURPOSE. Trolltech reserves all rights not granted ** herein. ** **********************************************************************/ /***************************************************************************** QValueVector documentation *****************************************************************************/ /*! \class QValueVector qvaluevector.h \brief The QValueVector class is a value-based template class that provides a dynamic array. \ingroup qtl \ingroup tools \ingroup shared \mainclass \reentrant QValueVector is a Qt implementation of an STL-like vector container. It can be used in your application if the standard \c vector is not available for your target platforms. QValueVector is part of the \link qtl.html Qt Template Library\endlink. QValueVector\ defines a template instance to create a vector of values that all have the class T. QValueVector does not store pointers to the members of the vector; it holds a copy of every member. QValueVector is said to be value based; in contrast, QPtrList and QDict are pointer based. QValueVector contains and manages a collection of objects of type T and provides random access iterators that allow the contained objects to be addressed. QValueVector owns the contained elements. For more relaxed ownership semantics, see QPtrCollection and friends, which are pointer-based containers. QValueVector provides good performance if you append or remove elements from the end of the vector. If you insert or remove elements from anywhere but the end, performance is very bad. The reason for this is that elements must to be copied into new positions. Some classes cannot be used within a QValueVector: for example, all classes derived from QObject and thus all classes that implement widgets. Only values can be used in a QValueVector. To qualify as a value the class must provide: \list \i a copy constructor; \i an assignment operator; \i a default constructor, i.e., a constructor that does not take any arguments. \endlist Note that C++ defaults to field-by-field assignment operators and copy constructors if no explicit version is supplied. In many cases this is sufficient. QValueVector uses an STL-like syntax to manipulate and address the objects it contains. See \link qtl.html this document\endlink for more information. Example: \code #include #include #include class Employee { public: Employee(): s(0) {} Employee( const QString& name, int salary ) : n( name ), s( salary ) { } QString name() const { return n; } int salary() const { return s; } void setSalary( int salary ) { s = salary; } private: QString n; int s; }; int main() { typedef QValueVector EmployeeVector; EmployeeVector vec( 3 ); // vector of 3 Employees vec[0] = Employee( "Bill", 50000 ); vec[1] = Employee( "Steve", 80000 ); vec[2] = Employee( "Ron", 60000 ); Employee joe( "Joe", 50000 ); vec.push_back( joe ); // vector expands to accommodate 4 Employees joe.setSalary( 70000 ); EmployeeVector::iterator it; for( it = vec.begin(); it != vec.end(); ++it ) printf( "%s earns %d\n", (*it).name().latin1(), (*it).salary() ); return 0; } \endcode Program output: \code Bill earns 50000 Steve earns 80000 Ron earns 60000 Joe earns 50000 \endcode As you can see, the most recent change to Joe's salary did not affect the value in the vector because the vector created a copy of Joe's entry. Many Qt functions return const value vectors; to iterate over these you should make a copy and iterate over the copy. There are several ways to find items in the vector. The begin() and end() functions return iterators to the beginning and end of the vector. The advantage of getting an iterator is that you can move forward or backward from this position by incrementing/decrementing the iterator. The iterator returned by end() points to the element which is one past the last element in the container. The past-the-end iterator is still associated with the vector it belongs to, however it is \e not dereferenceable; operator*() will not return a well-defined value. If the vector is empty(), the iterator returned by begin() will equal the iterator returned by end(). The fastest way to access an element of a vector is by using operator[]. This function provides random access and will return a reference to the element located at the specified index. Thus, you can access every element directly, in constant time, providing you know the location of the element. It is undefined to access an element that does not exist (your application will probably crash). For example: \code QValueVector vec1; // an empty vector vec1[10] = 4; // WARNING: undefined, probably a crash QValueVector vec2(25); // initialize with 25 elements vec2[10] = "Dave"; // OK \endcode Whenever inserting, removing or referencing elements in a vector, always make sure you are referring to valid positions. For example: \code void func( QValueVector& vec ) { if ( vec.size() > 10 ) { vec[9] = 99; // OK } }; \endcode The iterators provided by vector are random access iterators, therefore you can use them with many generic algorithms, for example, algorithms provided by the STL or the \link qtl.html QTL\endlink. Another way to find an element in the vector is by using the std::find() or \link qtl.html#qFind qFind()\endlink algorithms. For example: \code QValueVector vec; ... QValueVector::const_iterator it = qFind( vec.begin(), vec.end(), 3 ); if ( it != vector.end() ) // 'it' points to the found element \endcode It is safe to have multiple iterators on the vector at the same time. Since QValueVector manages memory dynamically, all iterators can become invalid if a memory reallocation occurs. For example, if some member of the vector is removed, iterators that point to the removed element and to all following elements become invalidated. Inserting into the middle of the vector will invalidate all iterators. For convenience, the function back() returns a reference to the last element in the vector, and front() returns a reference to the first element. If the vector is empty(), both back() and front() have undefined behavior (your application will crash or do unpredictable things). Use back() and front() with caution, for example: \code QValueVector vec( 3 ); vec.push_back( 1 ); vec.push_back( 2 ); vec.push_back( 3 ); ... if ( !vec.empty() ) { // OK: modify the first element int& i = vec.front(); i = 18; } ... QValueVector dvec; double d = dvec.back(); // undefined behavior \endcode Because QValueVector manages memory dynamically, it is recommended that you contruct a vector with an initial size. Inserting and removing elements happens fastest when: \list \i Inserting or removing elements happens at the end() of the vector; \i The vector does not need to allocate additional memory. \endlist By creating a QValueVector with a sufficiently large initial size, there will be less memory allocations. Do not use an initial size that is too big, since it will still take time to construct all the empty entries, and the extra space will be wasted if it is never used. Because QValueVector is value-based there is no need to be careful about deleting elements in the vector. The vector holds its own copies and will free them if the corresponding member or the vector itself is deleted. You can force the vector to free all of its items with clear(). QValueVector is shared implicitly, which means it can be copied in constant time. If multiple QValueVector instances share the same data and one needs to modify its contents, this modifying instance makes a copy and modifies its private copy; it thus does not affect the other instances. This is often called "copy on write". If a QValueVector is being used in a multi-threaded program, you must protect all access to the vector. See QMutex. There are several ways to insert elements into the vector. The push_back() function insert elements into the end of the vector, and is usually fastest. The insert() function can be used to add elements at specific positions within the vector. Items can be also be removed from the vector in several ways. There are several variants of the erase() function which removes a specific element, or range of elements, from the vector. Vectors can be also sorted with various STL algorithms , or it can be sorted using the \link qtl.html Qt Template Library\endlink. For example with qHeapSort(): Example: \code QValueVector v( 4 ); v.push_back( 5 ); v.push_back( 8 ); v.push_back( 3 ); v.push_back( 4 ); qHeapSort( v ); \endcode QValueVector stores its elements in contiguous memory. This means that you can use a QValueVector in any situation that retquires an array. */ /*! \enum QValueVector::value_type The type of the object stored in the vector. */ /*! \enum QValueVector::ValueType The type of the object stored in the vector. */ /*! \enum QValueVector::pointer The pointer to T type. */ /*! \enum QValueVector::const_pointer The const pointer to T type. */ /*! \enum QValueVector::iterator The vector's iterator type. */ /*! \enum QValueVector::const_iterator The vector's const iterator type. */ /*! \enum QValueVector::Iterator The vector's iterator type. */ /*! \enum QValueVector::ConstIterator The vector's const iterator type. */ /*! \enum QValueVector::reference The reference to T type. */ /*! \enum QValueVector::const_reference The const reference to T type. */ /*! \enum QValueVector::size_type An unsigned integral type, used to represent various sizes. */ /*! \enum QValueVector::difference_type A signed integral type used to represent the distance between two iterators. */ /*! \fn QValueVector::QValueVector() Constructs an empty vector without any elements. To create a vector which reserves an initial amount of space for elements, use \c QValueVector(size_type n). */ /*! \fn QValueVector::QValueVector( const QValueVector& v ) Constructs a copy of \a v. This operation costs O(1) time because QValueVector is implicitly shared. The first modification to the vector does takes O(n) time, because the elements must be copied. */ /*! \fn QValueVector::QValueVector( std::vector& v ) Constructs a copy of \a v. */ /*! \fn QValueVector::QValueVector( const std::vector& v ) This operation costs O(n) time because \a v is copied. */ /*! \fn QValueVector::QValueVector( size_type n, const T& val ) Constructs a vector with an initial size of \a n elements. Each element is initialized with the value of \a val. */ /*! \fn QValueVector::~QValueVector() Destroys the vector, destroying all elements and freeing the allocated memory. References to the values in the vector and all iterators of this vector become invalidated. Note that it is impossible for an iterator to check whether or not it is valid: QValueVector is tuned for performance, not for error checking. */ /*! \fn QValueVector& QValueVector::operator=( const QValueVector& v ) Assigns \a v to this vector and returns a reference to this vector. All iterators of the current vector become invalidated by this operation. The cost of such an assignment is O(1) since QValueVector is implicitly shared. */ /*! \fn QValueVector& QValueVector::operator=( const std::vector& v ) \overload Assigns \a v to this vector and returns a reference to this vector. All iterators of the current vector become invalidated by this operation. The cost of this assignment is O(n) since \a v is copied. */ /*! \fn size_type QValueVector::size() const Returns the number of elements in the vector. This function is provided for STL compatibility. It is equivalent to count(). \sa empty() */ /*! \fn size_type QValueVector::count() const Returns the number of items in the vector. \sa isEmpty() */ /*! \fn bool QValueVector::empty() const Returns TRUE if the vector is empty; otherwise returns FALSE. Equivalent to size()==0, only faster. This function is provided for STL compatibility. It is equivalent to isEmpty(). \sa size() */ /*! \fn bool QValueVector::isEmpty() const Returns TRUE if the vector is empty; returns FALSE otherwise. \sa count() */ /*! \fn size_type QValueVector::capacity() const Returns the maximum number of elements that can be stored in the vector without forcing memory reallocation. If memory reallocation takes place, some or all iterators may become invalidated. */ /*! \fn iterator QValueVector::begin() Returns an iterator pointing to the beginning of the vector. If the vector is empty(), the returned iterator will equal end(). */ /*! \fn const_iterator QValueVector::begin() const \overload Returns a const iterator pointing to the beginning of the vector. If the vector is empty(), the returned iterator will equal end(). */ /*! \fn const_iterator QValueVector::constBegin() const Returns a const iterator pointing to the beginning of the vector. If the vector is empty(), the returned iterator will equal end(). \sa constEnd(); */ /*! \fn iterator QValueVector::end() Returns an iterator pointing behind the last element of the vector. */ /*! \fn const_iterator QValueVector::end() const \overload Returns a const iterator pointing behind the last element of the vector. */ /*! \fn const_iterator QValueVector::constEnd() const Returns a const iterator pointing behind the last element of the vector. \sa constBegin() */ /*! \fn reference QValueVector::at( size_type i , bool* ok ) Returns a reference to the element with index \a i. If \a ok is non-null, and the index \a i is out of range, *\a ok is set to FALSE and the returned reference is undefined. If the index \a i is within the range of the vector, and \a ok is non-null, *\a ok is set to TRUE and the returned reference is well defined. */ /*! \fn const_reference QValueVector::at( size_type i , bool* ok ) const \overload Returns a const reference to the element with index \a i. If \a ok is non-null, and the index \a i is out of range, *\a ok is set to FALSE and the returned reference is undefined. If the index \a i is within the range of the vector, and \a ok is non-null, *\a ok is set to TRUE and the returned reference is well defined. */ /*! \fn reference QValueVector::operator[]( size_type i ) Returns a reference to the element at index \a i. If \a i is out of range, this function has undefined behavior. \sa at() */ /*! \fn const_reference QValueVector::operator[]( size_type i ) const \overload Returns a const reference to the element at index \a i. If \a i is out of range, this function has undefined behavior. \sa at() */ /*! \fn reference QValueVector::front() Returns a reference to the first element in the vector. If there is no first element, this function has undefined behavior. \sa empty() back() */ /*! \fn const_reference QValueVector::front() const \overload Returns a const reference to the first element in the vector. If there is no first element, this function has undefined behavior. \sa empty() back() */ /*! \fn reference QValueVector::first() Returns a reference to the first item in the vector. If there is no first item, this function has undefined behavior. \sa empty() last() */ /*! \fn const_reference QValueVector::first() const \overload */ /*! \fn reference QValueVector::back() Returns a reference to the last element in the vector. If there is no last element, this function has undefined behavior. \sa empty() front() */ /*! \fn const_reference QValueVector::back() const \overload Returns a const reference to the last element in the vector. If there is no last element, this function has undefined behavior. \sa empty() front() */ /*! \fn reference QValueVector::last() Returns a reference to the last item in the vector. If there is no last item, this function has undefined behavior. \sa empty() first() */ /*! \fn const_reference QValueVector::last() const \overload */ /*! \fn void QValueVector::push_back( const T& x ) Appends a copy of \a x to the end of the vector. This is the fastest way to add new elements. This function is provided for STL compatibility. It is equivalent to append(). \sa insert() */ /*! \fn void QValueVector::append( const T& x ) Appends a copy of \a x to the end of the vector. \sa push_back() insert() */ /*! \fn void QValueVector::pop_back() Removes the last item from the vector. This function is provided for STL compatibility. */ /*! \fn iterator QValueVector::insert( iterator pos, const T& x ) Inserts a copy of \a x at the position immediately before \a pos. \sa push_back() */ /*! \fn void QValueVector::detachInternal() \internal */ /*! \fn iterator QValueVector::insert( iterator pos, size_type n, const T& x ) \overload Inserts \a n copies of \a x immediately before position x. \sa push_back() */ /*! \fn void QValueVector::reserve( size_type n ) Increases the vector's capacity. If \a n is less than or equal to capacity(), nothing happens. Otherwise, additional memory is allocated so that capacity() will be increased to a value greater than or equal to \a n. All iterators will then become invalidated. Note that the vector's size() and the values of existing elements remain unchanged. */ /*! \fn void QValueVector::resize( size_type n, const T& val = T() ) Changes the size of the vector to \a n. If \a n is greater than the current size(), elements are added to the end and initialized with the value of \a val. If \a n is less than size(), elements are removed from the end. If \a n is equal to size() nothing happens. */ /*! \fn void QValueVector::clear() Removes all the elements from the vector. */ /*! \fn iterator QValueVector::erase( iterator pos ) Removes the element at position \a pos and returns the position of the next element. */ /*! \fn iterator QValueVector::erase( iterator first, iterator last ) \overload Removes all elements from \a first up to but not including \a last and returns the position of the next element. */ /*! \fn bool QValueVector::operator==( const QValueVector& x ) const Returns TRUE if each element in this vector equals each corresponding element in \a x; otherwise returns FALSE. */ /*! \fn bool QValueVector::operator==( const QValueVector& x ) \overload Returns TRUE if each element in this vector equals each corresponding element in \a x; otherwise returns FALSE. */ /*! \fn void QValueVector::detach() \internal If the vector does not share its data with another QValueVector instance, nothing happens. Otherwise the function creates a new copy of this data and detaches from the shared one. This function is called whenever the vector is modified. The implicit sharing mechanism is implemented this way. */