qhash.cpp

奇趣公司比较新的qt/emd版本

    the values for a single key, you can use values(const Key &key),
    which returns a QList<T>:

    \code
        QList<int> values = hash.values("plenty");
        for (int i = 0; i < values.size(); ++i)
            cout << values.at(i) << endl;
    \endcode

    The items that share the same key are available from most
    recently to least recently inserted. A more efficient approach is
    to call find() to get the iterator for the first item with a key
    and iterate from there:

    \code
        QHash<QString, int>::iterator i = hash.find("plenty");
        while (i != hash.end() && i.key() == "plenty") {
            cout << i.value() << endl;
            ++i;
        }
    \endcode

    If you only need to extract the values from a hash (not the keys),
    you can also use \l{foreach}:

    \code
        QHash<QString, int> hash;
        ...
        foreach (int value, hash)
            cout << value << endl;
    \endcode

    Items can be removed from the hash in several ways. One way is to
    call remove(); this will remove any item with the given key.
    Another way is to use QMutableHashIterator::remove(). In addition,
    you can clear the entire hash using clear().

    QHash's key and value data types must be \l{assignable data
    types}. You cannot, for example, store a QWidget as a value;
    instead, store a QWidget *. In addition, QHash's key type must
    provide operator==(), and there must also be a global qHash()
    function that returns a hash value for an argument of the key's
    type.

    Here's a list of the C++ and Qt types that can serve as keys in a
    QHash: any integer type (char, unsigned long, etc.), any pointer
    type, QChar, QString, and QByteArray. For all of these, the \c
    <QHash> header defines a qHash() function that computes an
    adequate hash value. If you want to use other types as the key,
    make sure that you provide operator==() and a qHash()
    implementation.

    Example:
    \code
        #ifndef EMPLOYEE_H
        #define EMPLOYEE_H

        class Employee
        {
        public:
            Employee() {}
            Employee(const QString &name, const QDate &dateOfBirth);
            ...

        private:
            QString myName;
            QDate myDateOfBirth;
        };

        inline bool operator==(const Employee &e1, const Employee &e2)
        {
            return e1.name() == e2.name()
                   && e1.dateOfBirth() == e2.dateOfBirth();
        }

        inline uint qHash(const Employee &key)
        {
            return qHash(key.name()) ^ key.dateOfBirth().day();
        }

        #endif // EMPLOYEE_H
    \endcode

    The qHash() function computes a numeric value based on a key. It
    can use any algorithm imaginable, as long as it always returns
    the same value if given the same argument. In other words, if
    \c{e1 == e2}, then \c{qHash(e1) == qHash(e2)} must hold as well.
    However, to obtain good performance, the qHash() function should
    attempt to return different hash values for different keys to the
    largest extent possible.

    In the example above, we've relied on Qt's global qHash(const
    QString &) to give us a hash value for the employee's name, and
    XOR'ed this with the day they were born to help produce unique
    hashes for people with the same name.

    Internally, QHash uses a hash table to perform lookups. Unlike Qt
    3's \c QDict class, which needed to be initialized with a prime
    number, QHash's hash table automatically grows and shrinks to
    provide fast lookups without wasting too much memory. You can
    still control the size of the hash table by calling reserve() if
    you already know approximately how many items the QHash will
    contain, but this isn't necessary to obtain good performance. You
    can also call capacity() to retrieve the hash table's size.

    \sa QHashIterator, QMutableHashIterator, QMap, QSet
*/

/*! \fn QHash::QHash()

    Constructs an empty hash.

    \sa clear()
*/

/*! \fn QHash::QHash(const QHash<Key, T> &other)

    Constructs a copy of \a other.

    This operation occurs in \l{constant time}, because QHash is
    \l{implicitly shared}. This makes returning a QHash from a
    function very fast. If a shared instance is modified, it will be
    copied (copy-on-write), and this takes \l{linear time}.

    \sa operator=()
*/

/*! \fn QHash::~QHash()

    Destroys the hash. References to the values in the hash and all
    iterators of this hash become invalid.
*/

/*! \fn QHash<Key, T> &QHash::operator=(const QHash<Key, T> &other)

    Assigns \a other to this hash and returns a reference to this hash.
*/

/*! \fn bool QHash::operator==(const QHash<Key, T> &other) const

    Returns true if \a other is equal to this hash; otherwise returns
    false.

    Two hashes are considered equal if they contain the same (key,
    value) pairs.

    This function requires the value type to implement \c operator==().

    \sa operator!=()
*/

/*! \fn bool QHash::operator!=(const QHash<Key, T> &other) const

    Returns true if \a other is not equal to this hash; otherwise
    returns false.

    Two hashes are considered equal if they contain the same (key,
    value) pairs.

    This function requires the value type to implement \c operator==().

    \sa operator==()
*/

/*! \fn int QHash::size() const

    Returns the number of items in the hash.

    \sa isEmpty(), count()
*/

/*! \fn bool QHash::isEmpty() const

    Returns true if the hash contains no items; otherwise returns
    false.

    \sa size()
*/

/*! \fn int QHash::capacity() const

    Returns the number of buckets in the QHash's internal hash table.

    The sole purpose of this function is to provide a means of fine
    tuning QHash'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 hash, call size().

    \sa reserve(), squeeze()
*/

/*! \fn void QHash::reserve(int size)

    Ensures that the QHash's internal hash table consists of at least
    \a size buckets.

    This function is useful for code that needs to build a huge hash
    and wants to avoid repeated reallocation. For example:

    \code
        QHash<QString, int> hash;
        hash.reserve(20000);
        for (int i = 0; i < 20000; ++i)
            hash.insert(keys[i], values[i]);
    \endcode

    Ideally, \a size should be slightly more than the maximum number
    of items expected in the hash. \a size doesn't have to be prime,
    because QHash will use a prime number internally anyway. If \a size
    is an underestimate, the worst that will happen is that the QHash
    will be a bit slower.

    In general, you will rarely ever need to call this function.
    QHash's internal hash table automatically shrinks or grows to
    provide good performance without wasting too much memory.

    \sa squeeze(), capacity()
*/

/*! \fn void QHash::squeeze()

    Reduces the size of the QHash's internal hash table to save
    memory.

    The sole purpose of this function is to provide a means of fine
    tuning QHash's memory usage. In general, you will rarely ever
    need to call this function.

    \sa reserve(), capacity()
*/

/*! \fn void QHash::detach()

    \internal

    Detaches this hash from any other hashes with which it may share
    data.

    \sa isDetached()
*/

/*! \fn bool QHash::isDetached() const

    \internal

    Returns true if the hash's internal data isn't shared with any
    other hash object; otherwise returns false.

    \sa detach()
*/

/*! \fn void QHash::setSharable(bool sharable)

    \internal
*/

/*! \fn void QHash::clear()

    Removes all items from the hash.

    \sa remove()
*/

/*! \fn int QHash::remove(const Key &key)

    Removes all the items that have the key \a key from the hash.
    Returns the number of items removed which is usually 1 but will
    be 0 if the key isn't in the hash, or greater than 1 if
    insertMulti() has been used with the \a key.

    \sa clear(), take(), QMultiHash::remove()
*/

/*! \fn T QHash::take(const Key &key)

    Removes the item with the key \a key from the hash and returns
    the value associated with it.

    If the item does not exist in the hash, the function simply
    returns a \l{default-constructed value}. If there are multiple
    items for \a key in the hash, only the most recently inserted one
    is removed.

    If you don't use the return value, remove() is more efficient.

    \sa remove()
*/

/*! \fn bool QHash::contains(const Key &key) const

    Returns true if the hash contains an item with key \a key;
    otherwise returns false.

    \sa count(), QMultiHash::contains()
*/

/*! \fn const T QHash::value(const Key &key) const

    Returns the value associated with the key \a key.

    If the hash contains no item with key \a key, the function
    returns a \l{default-constructed value}. If there are multiple
    items for \a key in the hash, the value of the most recently
    inserted one is returned.

    \sa key(), values(), contains(), operator[]()
*/

/*! \fn const T QHash::value(const Key &key, const T &defaultValue) const

    \overload

    If the hash contains no item with the given \a key, the function returns
    \a defaultValue.
*/

/*! \fn T &QHash::operator[](const Key &key)

    Returns the value associated with the key \a key as a modifiable
    reference.

    If the hash contains no item with key \a key, the function inserts
    a \l{default-constructed value} into the hash with key \a key, and
    returns a reference to it. If the hash contains multiple items
    with key \a key, this function returns a reference to the most
    recently inserted value.

    \sa insert(), value()
*/

/*! \fn const T QHash::operator[](const Key &key) const

    \overload

    Same as value().
*/

/*! \fn QList<Key> QHash::uniqueKeys() const
    \since 4.2

    Returns a list containing all the keys in the map in ascending
    order. Keys that occur multiple times in the map (because items
    were inserted with insertMulti(), or unite() was used) occur only
    once in the returned list.

    \sa keys(), values()
*/

/*! \fn QList<Key> QHash::keys() const

    Returns a list containing all the keys in the hash, in an
    arbitrary order. Keys that occur multiple times in the hash
    (because items were inserted with insertMulti(), or unite() was
    used) also occur multiple times in the list.

    To obtain a list of unique keys, where each key from the map only
    occurs once, use uniqueKeys().

    The order is guaranteed to be the same as that used by values().

    \sa uniqueKeys(), values(), key()
*/

/*! \fn QList<Key> QHash::keys(const T &value) const

    \overload

    Returns a list containing all the keys associated with value \a
    value, in an arbitrary order.

    This function can be slow (\l{linear time}), because QHash's
    internal data structure is optimized for fast lookup by key, not
    by value.
*/

/*! \fn QList<T> QHash::values() const

    Returns a list containing all the values in the hash, in an
    arbitrary order. If a key is associated multiple values, all of
    its values will be in the list, and not just the most recently
    inserted one.

    The order is guaranteed to be the same as that used by keys().

    \sa keys(), value()
*/

/*! \fn QList<T> QHash::values(const Key &key) const

    \overload

    Returns a list of all the values associated with key \a key,
    from the most recently inserted to the least recently inserted.

    \sa count(), insertMulti()
*/

/*! \fn Key QHash::key(const T &value) const

    Returns the first key with value \a value.

    If the hash contains no item with value \a value, the function
    returns a \link {default-constructed value} default-constructed
    key \endlink.

    This function can be slow (\l{linear time}), because QHash's
    internal data structure is optimized for fast lookup by key, not
    by value.

    \sa value(), keys()
*/

/*! 
    \fn Key QHash::key(const T &value, const Key &defaultKey) const
    \since 4.3
    \overload

    Returns the first key with value \a value, or \a defaultKey if
    the hash contains no item with value \a value.

    This function can be slow (\l{linear time}), because QHash's
    internal data structure is optimized for fast lookup by key, not
    by value.
*/

/*! \fn int QHash::count(const Key &key) const

    Returns the number of items associated with key \a key.

    \sa contains(), insertMulti()
*/

/*! \fn int QHash::count() const

    \overload

    Same as size().
*/

/*! \fn QHash::iterator QHash::begin()

    Returns an \l{STL-style iterator} pointing to the first item in
    the hash.

    \sa constBegin(), end()
*/

/*! \fn QHash::const_iterator QHash::begin() const

    \overload
*/

/*! \fn QHash::const_iterator QHash::constBegin() const

    Returns a const \l{STL-style iterator} pointing to the first item
    in the hash.

    \sa begin(), constEnd()
*/

/*! \fn QHash::iterator QHash::end()

    Returns an \l{STL-style iterator} pointing to the imaginary item
    after the last item in the hash.

    \sa begin(), constEnd()
*/

/*! \fn QHash::const_iterator QHash::end() const

    \overload
*/

/*! \fn QHash::const_iterator QHash::constEnd() const

    Returns a const \l{STL-style iterator} pointing to the imaginary
    item after the last item in the hash.

    \sa constBegin(), end()
*/

/*! \fn QHash::iterator QHash::erase(iterator pos)

    Removes the (key, value) pair associated with the iterator \a pos
    from the hash, and returns an iterator to the next item in the
    hash.

    Unlike remove() and take(), this function never causes QHash to
    rehash its internal data structure. This means that it can safely
    be called while iterating, and won't affect the order of items in
    the hash. For example:

    \code
        QHash<QObject *, int> objectHash;
        ...
        QHash<QObject *, int>::iterator i = objectHash.find(obj);
        while (i != objectHash.end() && i.key() == obj) {
            if (i.value() == 0) {
                i = objectHash.erase(i);
            } else {
                ++i;
            }
        }
    \endcode