/**************************************************************************** ** ** Copyright (C) 2011 Nokia Corporation and/or its subsidiary(-ies). ** All rights reserved. ** Contact: Nokia Corporation (qt-info@nokia.com) ** ** This file is part of the documentation of the Qt Toolkit. ** ** $QT_BEGIN_LICENSE:FDL$ ** GNU Free Documentation License ** Alternatively, this file may be used under the terms of the GNU Free ** Documentation License version 1.3 as published by the Free Software ** Foundation and appearing in the file included in the packaging of ** this file. ** ** Other Usage ** Alternatively, this file may be used in accordance with the terms ** and conditions contained in a signed written agreement between you ** and Nokia. ** ** ** ** ** $QT_END_LICENSE$ ** ****************************************************************************/ /*! \class QVarLengthArray \brief The QVarLengthArray class provides a low-level variable-length array. \ingroup tools \reentrant The C++ language doesn't support variable-length arrays on the stack. For example, the following code won't compile: \snippet doc/src/snippets/code/doc_src_qvarlengtharray.cpp 0 The alternative is to allocate the array on the heap (with \c{new}): \snippet doc/src/snippets/code/doc_src_qvarlengtharray.cpp 1 However, if myfunc() is called very frequently from the application's inner loop, heap allocation can be a major source of slowdown. QVarLengthArray is an attempt to work around this gap in the C++ language. It allocates a certain number of elements on the stack, and if you resize the array to a larger size, it automatically uses the heap instead. Stack allocation has the advantage that it is much faster than heap allocation. Example: \snippet doc/src/snippets/code/doc_src_qvarlengtharray.cpp 2 In the example above, QVarLengthArray will preallocate 1024 elements on the stack and use them unless \c{n + 1} is greater than 1024. If you omit the second template argument, QVarLengthArray's default of 256 is used. QVarLengthArray's value type must be an \l{assignable data type}. This covers most data types that are commonly used, but the compiler won't let you, for example, store a QWidget as a value; instead, store a QWidget *. QVarLengthArray, like QVector, provides a resizable array data structure. The main differences between the two classes are: \list \o QVarLengthArray's API is much more low-level. It provides no iterators and lacks much of QVector's functionality. \o QVarLengthArray doesn't initialize the memory if the value is a basic type. (QVector always does.) \o QVector uses \l{implicit sharing} as a memory optimization. QVarLengthArray doesn't provide that feature; however, it usually produces slightly better performance due to reduced overhead, especially in tight loops. \endlist In summary, QVarLengthArray is a low-level optimization class that only makes sense in very specific cases. It is used a few places inside Qt and was added to Qt's public API for the convenience of advanced users. \sa QVector, QList, QLinkedList */ /*! \fn QVarLengthArray::QVarLengthArray(int size) Constructs an array with an initial size of \a size elements. If the value type is a primitive type (e.g., char, int, float) or a pointer type (e.g., QWidget *), the elements are not initialized. For other types, the elements are initialized with a \l{default-constructed value}. */ /*! \fn QVarLengthArray::~QVarLengthArray() Destroys the array. */ /*! \fn int QVarLengthArray::size() const Returns the number of elements in the array. \sa isEmpty(), resize() */ /*! \fn int QVarLengthArray::count() const Same as size(). \sa isEmpty(), resize() */ /*! \fn bool QVarLengthArray::isEmpty() const Returns true if the array has size 0; otherwise returns false. \sa size(), resize() */ /*! \fn void QVarLengthArray::clear() Removes all the elements from the array. Same as resize(0). */ /*! \fn void QVarLengthArray::resize(int size) Sets the size of the array to \a size. If \a size is greater than the current size, elements are added to the end. If \a size is less than the current size, elements are removed from the end. If the value type is a primitive type (e.g., char, int, float) or a pointer type (e.g., QWidget *), new elements are not initialized. For other types, the elements are initialized with a \l{default-constructed value}. \sa size() */ /*! \fn int QVarLengthArray::capacity() const Returns the maximum number of elements that can be stored in the array without forcing a reallocation. The sole purpose of this function is to provide a means of fine tuning QVarLengthArray's memory usage. In general, you will rarely ever need to call this function. If you want to know how many items are in the array, call size(). \sa reserve() */ /*! \fn void QVarLengthArray::reserve(int size) Attempts to allocate memory for at least \a size elements. If you know in advance how large the array can get, you can call this function and if you call resize() often, you are likely to get better performance. If \a size is an underestimate, the worst that will happen is that the QVarLengthArray will be a bit slower. The sole purpose of this function is to provide a means of fine tuning QVarLengthArray's memory usage. In general, you will rarely ever need to call this function. If you want to change the size of the array, call resize(). \sa capacity() */ /*! \fn T &QVarLengthArray::operator[](int i) Returns a reference to the item at index position \a i. \a i must be a valid index position in the array (i.e., 0 <= \a i < size()). \sa data(), at() */ /*! \fn const T &QVarLengthArray::operator[](int i) const \overload */ /*! \fn void QVarLengthArray::append(const T &t) Appends item \a t to the array, extending the array if necessary. \sa removeLast() */ /*! \fn inline void QVarLengthArray::removeLast() \since 4.5 Decreases the size of the array by one. The allocated size is not changed. \sa append() */ /*! \fn void QVarLengthArray::append(const T *buf, int size) Appends \a size amount of items referenced by \a buf to this array. */ /*! \fn T *QVarLengthArray::data() Returns a pointer to the data stored in the array. The pointer can be used to access and modify the items in the array. Example: \snippet doc/src/snippets/code/doc_src_qvarlengtharray.cpp 3 The pointer remains valid as long as the array isn't reallocated. This function is mostly useful to pass an array to a function that accepts a plain C++ array. \sa constData(), operator[]() */ /*! \fn const T *QVarLengthArray::data() const \overload */ /*! \fn const T *QVarLengthArray::constData() const Returns a const pointer to the data stored in the array. The pointer can be used to access the items in the array. The pointer remains valid as long as the array isn't reallocated. This function is mostly useful to pass an array to a function that accepts a plain C++ array. \sa data(), operator[]() */ /*! \fn QVarLengthArray &QVarLengthArray::operator=(const QVarLengthArray &other) Assigns \a other to this array and returns a reference to this array. */ /*! \fn QVarLengthArray::QVarLengthArray(const QVarLengthArray &other) Constructs a copy of \a other. */ /*! \fn const T &QVarLengthArray::at(int i) const Returns a reference to the item at index position \a i. \a i must be a valid index position in the array (i.e., 0 <= \a i < size()). \sa value(), operator[]() */ /*! \fn T QVarLengthArray::value(int i) const Returns the value at index position \a i. If the index \a i is out of bounds, the function returns a \l{default-constructed value}. If you are certain that \a i is within bounds, you can use at() instead, which is slightly faster. \sa at(), operator[]() */ /*! \fn T QVarLengthArray::value(int i, const T &defaultValue) const \overload If the index \a i is out of bounds, the function returns \a defaultValue. */ /*! \typedef QVarLengthArray::size_type \since 4.7 Typedef for int. Provided for STL compatibility. */ /*! \typedef QVarLengthArray::value_type \since 4.7 Typedef for T. Provided for STL compatibility. */ /*! \typedef QVarLengthArray::difference_type \since 4.7 Typedef for ptrdiff_t. Provided for STL compatibility. */ /*! \typedef QVarLengthArray::pointer \since 4.7 Typedef for T *. Provided for STL compatibility. */ /*! \typedef QVarLengthArray::const_pointer \since 4.7 Typedef for const T *. Provided for STL compatibility. */ /*! \typedef QVarLengthArray::reference \since 4.7 Typedef for T &. Provided for STL compatibility. */ /*! \typedef QVarLengthArray::const_reference \since 4.7 Typedef for const T &. Provided for STL compatibility. */ /*! \fn void QVarLengthArray::prepend(const T &value) \since 4.8 Inserts \a value at the beginning of the array. This is the same as vector.insert(0, \a value). For large arrays, this operation can be slow (\l{linear time}), because it requires moving all the items in the vector by one position further in memory. If you want a container class that provides a fast prepend() function, use QList or QLinkedList instead. \sa append(), insert() */ /*! \fn void QVarLengthArray::replace(int i, const T &value) \since 4.8 Replaces the item at index position \a i with \a value. \a i must be a valid index position in the array (i.e., 0 <= \a i < size()). \sa operator[](), remove() */ /*! \fn void QVarLengthArray::remove(int i) \overload \since 4.8 Removes the element at index position \a i. \sa insert(), replace() */ /*! \fn void QVarLengthArray::remove(int i, int count) \overload \since 4.8 Removes \a count elements from the middle of the array, starting at index position \a i. \sa insert(), replace() */ /*! \fn QVarLengthArray::iterator QVarLengthArray::begin() \since 4.8 Returns an \l{STL-style iterator} pointing to the first item in the array. \sa constBegin(), end() */ /*! \fn QVarLengthArray::const_iterator QVarLengthArray::begin() const \since 4.8 \overload */ /*! \fn QVarLengthArray::const_iterator QVarLengthArray::constBegin() const \since 4.8 Returns a const \l{STL-style iterator} pointing to the first item in the array. \sa begin(), constEnd() */ /*! \fn QVarLengthArray::iterator QVarLengthArray::end() \since 4.8 Returns an \l{STL-style iterator} pointing to the imaginary item after the last item in the array. \sa begin(), constEnd() */ /*! \fn QVarLengthArray::const_iterator QVarLengthArray::end() const \since 4.8 \overload */ /*! \fn QVarLengthArray::const_iterator QVarLengthArray::constEnd() const \since 4.8 Returns a const \l{STL-style iterator} pointing to the imaginary item after the last item in the array. \sa constBegin(), end() */ /*! \fn QVarLengthArray::iterator QVarLengthArray::erase(iterator pos) \since 4.8 Removes the item pointed to by the iterator \a pos from the vector, and returns an iterator to the next item in the vector (which may be end()). \sa insert(), remove() */ /*! \fn QVarLengthArray::iterator QVarLengthArray::erase(iterator begin, iterator end) \overload \since 4.8 Removes all the items from \a begin up to (but not including) \a end. Returns an iterator to the same item that \a end referred to before the call. */ /*! \fn void QVarLengthArray::insert(int i, const T &value) \since 4.8 Inserts \a value at index position \a i in the array. If \a i is 0, the value is prepended to the vector. If \a i is size(), the value is appended to the vector. For large arrays, this operation can be slow (\l{linear time}), because it requires moving all the items at indexes \a i and above by one position further in memory. If you want a container class that provides a fast insert() function, use QLinkedList instead. \sa remove() */ /*! \fn void QVarLengthArray::insert(int i, int count, const T &value) \overload \since 4.8 Inserts \a count copies of \a value at index position \a i in the vector. */ /*! \fn QVarLengthArray::iterator QVarLengthArray::insert(iterator before, const T &value) \overload \since 4.8 Inserts \a value in front of the item pointed to by the iterator \a before. Returns an iterator pointing at the inserted item. */ /*! \fn QVarLengthArray::iterator QVarLengthArray::insert(iterator before, int count, const T &value) \since 4.8 Inserts \a count copies of \a value in front of the item pointed to by the iterator \a before. Returns an iterator pointing at the first of the inserted items. */ /*! \fn bool operator==(const QVarLengthArray &left, const QVarLengthArray &right) \relates QVarLengthArray \since 4.8 Returns true if the two array are equal; Two arrays are considered equal if they contain the same values in the same order. This function requires the value type to have an implementation of \c operator==(). \sa operator!=() */ /*! \fn bool operator!=(const QVarLengthArray &left, const QVarLengthArray &right) \relates QVarLengthArray \since 4.8 Returns true if the two array are different; Two arrays are considered equal if they contain the same values in the same order. This function requires the value type to have an implementation of \c operator==(). \sa operator==() */ /*! \fn QVarLengthArray &QVarLengthArray::operator<<(const T &value) \since 4.8 Appends \a value to the array and returns a reference to this vector. \sa append(), operator+=() */ /*! \fn QVarLengthArray &QVarLengthArray::operator+=(const T &value) \since 4.8 Appends \a value to the array and returns a reference to this vector. \sa append(), operator<<() */