qalgorithms.qdoc

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// Copyright (C) 2016 The Qt Company Ltd.
// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR GFDL-1.3-no-invariants-only
 
/*!
    \headerfile <QtAlgorithms>
    \inmodule QtCore
    \title Generic Algorithms
    \ingroup funclists
    \keyword generic algorithms
 
    \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 small tasks to
    make life easier, such as qDeleteAll(), which invokes \c{operator delete}
    on all items in a given container or in a given range.
    You can use these algorithms with any \l {container
    class} that provides STL-style iterators, including Qt's QList,
    QMap, and QHash classes.
 
    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.
 
    Different algorithms can have different requirements for the
    iterators they accept. 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 Iterators}{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, 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.
 
    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.
 
    \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 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 \li \c{i += n} \li advances iterator \c i by \c n positions
    \row \li \c{i -= n} \li moves iterator \c i back by \c n positions
    \row \li \c{i + n} or \c{n + i} \li returns the iterator for the item \c
       n positions ahead of iterator \c i
    \row \li \c{i - n} \li returns the iterator for the item \c n positions behind of iterator \c i
    \row \li \c{i - j} \li returns the number of items between iterators \c i and \c j
    \row \li \c{i[n]} \li same as \c{*(i + n)}
    \row \li \c{i < j} \li returns \c true if iterator \c j comes after iterator \c i
    \endtable
 
    QList's non-const iterator type is random access iterator.
 
    \sa {container classes}, <QtGlobal>
*/
 
/*!
    \fn template <typename ForwardIterator> void qDeleteAll(ForwardIterator begin, ForwardIterator end)
    \relates <QtAlgorithms>
 
    Deletes all the items in the range [\a begin, \a end) using the
    C++ \c delete operator. The item type must be a pointer type (for
    example, \c{QWidget *}).
 
    Example:
    \snippet code/doc_src_qalgorithms.cpp 1
 
    Notice that qDeleteAll() doesn't remove the items from the
    container; it merely calls \c delete on them. In the example
    above, we call clear() on the container to remove the items.
 
    This function can also be used to delete items stored in
    associative containers, such as QMap and QHash. Only the objects
    stored in each container will be deleted by this function; objects
    used as keys will not be deleted.
 
    \sa {forward iterators}
*/
 
/*!
    \fn template <typename Container> void qDeleteAll(const Container &c)
    \relates <QtAlgorithms>
 
    \overload
 
    This is the same as qDeleteAll(\a{c}.begin(), \a{c}.end()).
*/
 
/*!
    \fn uint qPopulationCount(quint8 v)
    \relates <QtAlgorithms>
    \since 5.2
 
    Returns the number of bits set in \a v. This number is also called
    the Hamming Weight of \a v.
 */
 
/*!
    \fn uint qPopulationCount(quint16 v)
    \relates <QtAlgorithms>
    \since 5.2
    \overload
 */
 
/*!
    \fn uint qPopulationCount(quint32 v)
    \relates <QtAlgorithms>
    \since 5.2
    \overload
 */
 
/*!
    \fn uint qPopulationCount(quint64 v)
    \relates <QtAlgorithms>
    \since 5.2
    \overload
 */
 
/*!
    \fn uint qCountTrailingZeroBits(quint8 v)
    \relates <QtAlgorithms>
    \since 5.6
 
    Returns the number of consecutive zero bits in \a v, when searching from the LSB.
    For example, qCountTrailingZeroBits(1) returns 0 and qCountTrailingZeroBits(8) returns 3.
 */
 
/*!
    \fn uint qCountTrailingZeroBits(quint16 v)
    \relates <QtAlgorithms>
    \since 5.6
    \overload
 */
 
/*!
    \fn uint qCountTrailingZeroBits(quint32 v)
    \relates <QtAlgorithms>
    \since 5.6
    \overload
 */
 
/*!
    \fn uint qCountTrailingZeroBits(quint64 v)
    \relates <QtAlgorithms>
    \since 5.6
    \overload
 */
 
/*!
    \fn uint qCountLeadingZeroBits(quint8 v)
    \relates <QtAlgorithms>
    \since 5.6
 
    Returns the number of consecutive zero bits in \a v, when searching from the MSB.
    For example, qCountLeadingZeroBits(quint8(1)) returns 7 and
    qCountLeadingZeroBits(quint8(8)) returns 4.
 */
 
/*!
    \fn uint qCountLeadingZeroBits(quint16 v)
    \relates <QtAlgorithms>
    \since 5.6
 
    Returns the number of consecutive zero bits in \a v, when searching from the MSB.
    For example, qCountLeadingZeroBits(quint16(1)) returns 15 and
    qCountLeadingZeroBits(quint16(8)) returns 12.
 */
 
/*!
    \fn uint qCountLeadingZeroBits(quint32 v)
    \relates <QtAlgorithms>
    \since 5.6
 
    Returns the number of consecutive zero bits in \a v, when searching from the MSB.
    For example, qCountLeadingZeroBits(quint32(1)) returns 31 and
    qCountLeadingZeroBits(quint32(8)) returns 28.
 */
 
/*!
    \fn uint qCountLeadingZeroBits(quint64 v)
    \relates <QtAlgorithms>
    \since 5.6
 
    Returns the number of consecutive zero bits in \a v, when searching from the MSB.
    For example, qCountLeadingZeroBits(quint64(1)) returns 63 and
    qCountLeadingZeroBits(quint64(8)) returns 60.
 */
 
/*!
    \fn template <typename InputIterator, typename Result, typename Separator = Result, typename Projection = q20::identity> Result qJoin(InputIterator first, InputIterator last, Result init, const Separator &separator, Projection p)
    \relates <QtAlgorithms>
    \since 6.10
 
    Starts with initial value \a init and cumulatively adds to it each entry in
    the range from \a first to \a last. Each entry is, before adding, mapped
    through the projection \a p (which defaults to the identity). Between each
    entry and the next, an optional \a separator is added. For example:
 
    \code
        QList<int> l = {1, 2, 3};
        QString res = qJoin(l.cbegin(), l.cend(), QString(), u" / ",
                            [](int n) { return QString::number(2 * n);});
        // res == "2 / 4 / 6"
    \endcode
 
    \note \c{q20::identity} is a C++17 backport of C++20's
    \l{https://en.cppreference.com/w/cpp/utility/functional/identity}{\c{std::identity}}.
*/