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/*!

    \headerfile <QtAlgorithms>

    \title Generic Algorithms

    \ingroup funclists

    \brief The <QtAlgorithms> header includes the generic, template-based algorithms.

    Qt provides a number of global template functions in \c

    <QtAlgorithms> that work on containers and perform well-know

    algorithms. You can use these algorithms with any \l {container

    class} that provides STL-style iterators, including Qt's QList,

    QLinkedList, QVector, QMap, and QHash classes.

    These functions have taken their inspiration from similar

    functions available in the STL \c <algorithm> header. Most of them

    have a direct STL equivalent; for example, qCopyBackward() is the

    same as STL's copy_backward() algorithm.

    If STL is available on all your target platforms, you can use the

    STL algorithms instead of their Qt counterparts. One reason why

    you might want to use the STL algorithms is that STL provides

    dozens and dozens of algorithms, whereas Qt only provides the most

    important ones, making no attempt to duplicate functionality that

    is already provided by the C++ standard.

    Most algorithms take \l {STL-style iterators} as parameters. The

    algorithms are generic in the sense that they aren't bound to a

    specific iterator class; you can use them with any iterators that

    meet a certain set of requirements.

    Let's take the qFill() algorithm as an example. Unlike QVector,

    QList has no fill() function that can be used to fill a list with

    a particular value. If you need that functionality, you can use

    qFill():

    \snippet doc/src/snippets/code/doc_src_qalgorithms.qdoc 0

    qFill() takes a begin iterator, an end iterator, and a value.

    In the example above, we pass \c list.begin() and \c list.end()

    as the begin and end iterators, but this doesn't have to be

    the case:

    \snippet doc/src/snippets/code/doc_src_qalgorithms.qdoc 1

    Different algorithms can have different requirements for the

    iterators they accept. For example, qFill() accepts two 

    \l {forward iterators}. The iterator types required are specified

    for each algorithm. If an iterator of the wrong type is passed (for

    example, if QList::ConstIterator is passed as an \l {output

    iterator}), you will always get a compiler error, although not

    necessarily a very informative one.

    Some algorithms have special requirements on the value type

    stored in the containers. For example, qEqual() requires that the

    value type supports operator==(), which it uses to compare items.

    Similarly, qDeleteAll() requires that the value type is a

    non-const pointer type (for example, QWidget *). The value type

    requirements are specified for each algorithm, and the compiler

    will produce an error if a requirement isn't met.

    \target binaryFind example

    The generic algorithms can be used on other container classes

    than those provided by Qt and STL. The syntax of STL-style

    iterators is modeled after C++ pointers, so it's possible to use

    plain arrays as containers and plain pointers as iterators. A

    common idiom is to use qBinaryFind() together with two static

    arrays: one that contains a list of keys, and another that

    contains a list of associated values. For example, the following

    code will look up an HTML entity (e.g., \c &) in the \c

    name_table array and return the corresponding Unicode value from

    the \c value_table if the entity is recognized:

    \snippet doc/src/snippets/code/doc_src_qalgorithms.qdoc 2

    This kind of code is for advanced users only; for most

    applications, a QMap- or QHash-based approach would work just as

    well:

    \snippet doc/src/snippets/code/doc_src_qalgorithms.qdoc 3

    \section1 Types of Iterators

    The algorithms have certain requirements on the iterator types

    they accept, and these are specified individually for each

    function. The compiler will produce an error if a requirement

    isn't met.

    \section2 Input Iterators

    An \e{input iterator} is an iterator that can be used for reading

    data sequentially from a container. It must provide the following

    operators: \c{==} and \c{!=} for comparing two iterators, unary

    \c{*} for retrieving the value stored in the item, and prefix

    \c{++} for advancing to the next item.

    The Qt containers' iterator types (const and non-const) are all

    input iterators.

    \section2 Output Iterators

    An \e{output iterator} is an iterator that can be used for

    writing data sequentially to a container or to some output

    stream. It must provide the following operators: unary \c{*} for

    writing a value (i.e., \c{*it = val}) and prefix \c{++} for

    advancing to the next item.

    The Qt containers' non-const iterator types are all output

    iterators.

    \section2 Forward Iterators

    A \e{forward iterator} is an iterator that meets the requirements

    of both input iterators and output iterators.

    The Qt containers' non-const iterator types are all forward

    iterators.

    \section2 Bidirectional Iterators

    A \e{bidirectional iterator} is an iterator that meets the

    requirements of forward iterators but that in addition supports

    prefix \c{--} for iterating backward.

    The Qt containers' non-const iterator types are all bidirectional

    iterators.

    \section2 Random Access Iterators

    The last category, \e{random access iterators}, is the most

    powerful type of iterator. It supports all the requirements of a

    bidirectional iterator, and supports the following operations:

    \table

    \row \i \c{i += n} \i advances iterator \c i by \c n positions

    \row \i \c{i -= n} \i moves iterator \c i back by \c n positions

    \row \i \c{i + n} or \c{n + i} \i returns the iterator for the item \c

       n positions ahead of iterator \c i

    \row \i \c{i - n} \i returns the iterator for the item \c n positions behind of iterator \c i

    \row \i \c{i - j} \i returns the number of items between iterators \c i and \c j

    \row \i \c{i[n]} \i same as \c{*(i + n)}

    \row \i \c{i < j} \i returns true if iterator \c j comes after iterator \c i

    \endtable

    QList and QVector's non-const iterator types are random access iterators.

    \sa {container classes}, <QtGlobal>

*/

/*! \fn OutputIterator qCopy(InputIterator begin1, InputIterator end1, OutputIterator begin2)

    \relates <QtAlgorithms>

    Copies the items from range [\a begin1, \a end1) to range [\a

    begin2, ...), in the order in which they appear.

    The item at position \a begin1 is assigned to that at position \a

    begin2; the item at position \a begin1 + 1 is assigned to that at

    position \a begin2 + 1; and so on.

    Example:

    \snippet doc/src/snippets/code/doc_src_qalgorithms.qdoc 4

    \sa qCopyBackward(), {input iterators}, {output iterators}

*/

/*! \fn BiIterator2 qCopyBackward(BiIterator1 begin1, BiIterator1 end1, BiIterator2 end2)

    \relates <QtAlgorithms>

    Copies the items from range [\a begin1, \a end1) to range [...,

    \a end2).

    The item at position \a end1 - 1 is assigned to that at position

    \a end2 - 1; the item at position \a end1 - 2 is assigned to that

    at position \a end2 - 2; and so on.

    Example:

    \snippet doc/src/snippets/code/doc_src_qalgorithms.qdoc 5

    \sa qCopy(), {bidirectional iterators}

*/

/*! \fn bool qEqual(InputIterator1 begin1, InputIterator1 end1, InputIterator2 begin2)

    \relates <QtAlgorithms>

    Compares the items in the range [\a begin1, \a end1) with the

    items in the range [\a begin2, ...). Returns true if all the

    items compare equal; otherwise returns false.

    Example:

    \snippet doc/src/snippets/code/doc_src_qalgorithms.qdoc 6

    This function requires the item type (in the example above,

    QString) to implement \c operator==().

    \sa {input iterators}

*/

/*! \fn void qFill(ForwardIterator begin, ForwardIterator end, const T &value)

    \relates <QtAlgorithms>

    Fills the range [\a begin, \a end) with \a value.

    Example:

    \snippet doc/src/snippets/code/doc_src_qalgorithms.qdoc 7

    \sa qCopy(), {forward iterators}

*/

/*! \fn void qFill(Container &container, const T &value)

    \relates <QtAlgorithms>

    \overload

    This is the same as qFill(\a{container}.begin(), \a{container}.end(), \a value);

*/

/*! \fn InputIterator qFind(InputIterator begin, InputIterator end, const T &value)

    \relates <QtAlgorithms>

    Returns an iterator to the first occurrence of \a value in a

    container in the range [\a begin, \a end). Returns \a end if \a

    value isn't found.

    Example:

    \snippet doc/src/snippets/code/doc_src_qalgorithms.qdoc 8

    This function requires the item type (in the example above,

    QString) to implement \c operator==().

    If the items in the range are in ascending order, you can get

    faster results by using qLowerBound() or qBinaryFind() instead of

    qFind().

    \sa qBinaryFind(), {input iterators}

*/

/*! \fn void qFind(const Container &container, const T &value)

    \relates <QtAlgorithms>

    \overload

    This is the same as qFind(\a{container}.begin(), \a{container}.end(), value);

*/

/*! \fn void qCount(InputIterator begin, InputIterator end, const T &value, Size &n)

    \relates <QtAlgorithms>

    Returns the number of occurrences of \a value in the range [\a begin, \a end),

    which is returned in \a n. \a n is never initialized, the count is added to \a n.

    It is the caller's responsibility to initialize \a n.

    Example:

    \snippet doc/src/snippets/code/doc_src_qalgorithms.qdoc 9

    This function requires the item type (in the example above,

    \c int) to implement \c operator==().

    \sa {input iterators}

*/

/*! \fn void qCount(const Container &container, const T &value, Size &n)

\relates <QtAlgorithms>

\overload

Instead of operating on iterators, as in the other overload, this function

operates on the specified \a container to obtain the number of instances

of \a value in the variable passed as a reference in argument \a n.

*/

/*! \fn void qSwap(T &var1, T &var2)

    \relates <QtAlgorithms>

    Exchanges the values of variables \a var1 and \a var2.

    Example:

    \snippet doc/src/snippets/code/doc_src_qalgorithms.qdoc 10

*/

/*! \fn void qSort(RandomAccessIterator begin, RandomAccessIterator end)

    \relates <QtAlgorithms>

    Sorts the items in range [\a begin, \a end) in ascending order

    using the quicksort algorithm.

    Example:

    \snippet doc/src/snippets/code/doc_src_qalgorithms.qdoc 11

    The sort algorithm is efficient on large data sets. It operates

    in \l {linear-logarithmic time}, O(\e{n} log \e{n}).

    This function requires the item type (in the example above,

    \c{int}) to implement \c operator<().

    If neither of the two items is "less than" the other, the items are

    taken to be equal. It is then undefined which one of the two

    items will appear before the other after the sort.

    \sa qStableSort(), {random access iterators}

*/

/*! \fn void qSort(RandomAccessIterator begin, RandomAccessIterator end, LessThan lessThan)

    \relates <QtAlgorithms>

    \overload

    Uses the \a lessThan function instead of \c operator<() to

    compare the items.

    For example, here's how to sort the strings in a QStringList

    in case-insensitive alphabetical order:

    \snippet doc/src/snippets/code/doc_src_qalgorithms.qdoc 12

    To sort values in reverse order, pass

    \l{qGreater()}{qGreater<T>()} as the \a lessThan parameter. For

    example:

    \snippet doc/src/snippets/code/doc_src_qalgorithms.qdoc 13

    If neither of the two items is "less than" the other, the items are

    taken to be equal. It is then undefined which one of the two

    items will appear before the other after the sort.

    An alternative to using qSort() is to put the items to sort in a

    QMap, using the sort key as the QMap key. This is often more

    convenient than defining a \a lessThan function. For example, the

    following code shows how to sort a list of strings case

    insensitively using QMap:

    \snippet doc/src/snippets/code/doc_src_qalgorithms.qdoc 14

    \sa QMap

*/

/*! \fn void qSort(Container &container)

    \relates <QtAlgorithms>

    \overload

    This is the same as qSort(\a{container}.begin(), \a{container}.end());

*/

/*! 

    \fn void qStableSort(RandomAccessIterator begin, RandomAccessIterator end)

    \relates <QtAlgorithms>

    Sorts the items in range [\a begin, \a end) in ascending order

    using a stable sorting algorithm.

    If neither of the two items is "less than" the other, the items are

    taken to be equal. The item that appeared before the other in the

    original container will still appear first after the sort. This

    property is often useful when sorting user-visible data.

    Example:

    \snippet doc/src/snippets/code/doc_src_qalgorithms.qdoc 15

    The sort algorithm is efficient on large data sets. It operates

    in \l {linear-logarithmic time}, O(\e{n} log \e{n}).

    This function requires the item type (in the example above,

    \c{int}) to implement \c operator<().

    \sa qSort(), {random access iterators}

*/

/*! 

    \fn void qStableSort(RandomAccessIterator begin, RandomAccessIterator end, LessThan lessThan)

    \relates <QtAlgorithms>

    \overload

    Uses the \a lessThan function instead of \c operator<() to

    compare the items.

    For example, here's how to sort the strings in a QStringList

    in case-insensitive alphabetical order:

    \snippet doc/src/snippets/code/doc_src_qalgorithms.qdoc 16

    Note that earlier versions of Qt allowed using a lessThan function that took its

    arguments by non-const reference. From 4.3 and on this is no longer possible,

    the arguments has to be passed by const reference or value.

    To sort values in reverse order, pass

    \l{qGreater()}{qGreater<T>()} as the \a lessThan parameter. For

    example:

    \snippet doc/src/snippets/code/doc_src_qalgorithms.qdoc 17

    If neither of the two items is "less than" the other, the items are

    taken to be equal. The item that appeared before the other in the

    original container will still appear first after the sort. This

    property is often useful when sorting user-visible data.

*/

/*! 

    \fn void qStableSort(Container &container)

    \relates <QtAlgorithms>

    \overload

    This is the same as qStableSort(\a{container}.begin(), \a{container}.end());

*/

/*! \fn RandomAccessIterator qLowerBound(RandomAccessIterator begin, RandomAccessIterator end, const T &value)

    \relates <QtAlgorithms>

    Performs a binary search of the range [\a begin, \a end) and

    returns the position of the first ocurrence of \a value. If no

    such item is found, returns the position where it should be

    inserted.

    The items in the range [\a begin, \e end) must be sorted in

    ascending order; see qSort().

    Example:

    \snippet doc/src/snippets/code/doc_src_qalgorithms.qdoc 18

    This function requires the item type (in the example above,

    \c{int}) to implement \c operator<().

    qLowerBound() can be used in conjunction with qUpperBound() to

    iterate over all occurrences of the same value:

    \snippet doc/src/snippets/code/doc_src_qalgorithms.qdoc 19

    \sa qUpperBound(), qBinaryFind()

*/

/*!

    \fn RandomAccessIterator qLowerBound(RandomAccessIterator begin, RandomAccessIterator end, const T &value, LessThan lessThan)

    \relates <QtAlgorithms>

    \overload

    Uses the \a lessThan function instead of \c operator<() to

    compare the items.

    Note that the items in the range must be sorted according to the order

    specified by the \a lessThan object.

*/

/*! 

    \fn void qLowerBound(const Container &container, const T &value)

    \relates <QtAlgorithms>

    \overload

    For read-only iteration over containers, this function is broadly equivalent to

    qLowerBound(\a{container}.begin(), \a{container}.end(), value). However, since it

    returns a const iterator, you cannot use it to modify the container; for example,

    to insert items.

*/

/*! \fn RandomAccessIterator qUpperBound(RandomAccessIterator begin, RandomAccessIterator end, const T &value)

    \relates <QtAlgorithms>

    Performs a binary search of the range [\a begin, \a end) and

    returns the position of the one-past-the-last occurrence of \a

    value. If no such item is found, returns the position where the

    item should be inserted.

    The items in the range [\a begin, \e end) must be sorted in

    ascending order; see qSort().

    Example:

    \snippet doc/src/snippets/code/doc_src_qalgorithms.qdoc 20

    This function requires the item type (in the example above,

    \c{int}) to implement \c operator<().

    qUpperBound() can be used in conjunction with qLowerBound() to

    iterate over all occurrences of the same value:

    \snippet doc/src/snippets/code/doc_src_qalgorithms.qdoc 21

    \sa qLowerBound(), qBinaryFind()

*/

/*!

    \fn RandomAccessIterator qUpperBound(RandomAccessIterator begin, RandomAccessIterator end, const T &value, LessThan lessThan)

    \relates <QtAlgorithms>

    \overload