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/****************************************************************************
**
** 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.
**
** $QT_BEGIN_LICENSE:FDL$
** No Commercial Usage
** This file contains pre-release code and may not be distributed.
** You may use this file in accordance with the terms and conditions
** contained in the Technology Preview License Agreement accompanying
** this package.
**
** 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.
**
** If you have questions regarding the use of this file, please contact
** Nokia at qt-info@nokia.com.
** $QT_END_LICENSE$
**
****************************************************************************/
/*!
\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<T, Prealloc> &QVarLengthArray::operator=(const QVarLengthArray<T, Prealloc> &other)
Assigns \a other to this array and returns a reference to this array.
*/
/*! \fn QVarLengthArray::QVarLengthArray(const QVarLengthArray<T, Prealloc> &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.
*/
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