CopperSpice API  1.7.2
QMultiHash< Key, Val, Hash, KeyEqual >::iterator Class Reference

STL style non-const iterator for QMultiHash. More...

Public Typedefs

using iterator_category = std::forward_iterator_tag
 
using pointer = Val *
 
using reference = Val &
 
using size_type = typename std::unordered_multimap< Key, Val, Hash, KeyEqual >::difference_type
 

Public Methods

 iterator () = default
 
const Key & key () const
 
bool operator!= (iterator other) const
 
Val & operator* () const
 
iterator operator+ (size_type n) const
 
iterator & operator++ ()
 
iterator operator++ (int)
 
iterator & operator+= (size_type n)
 
iterator operator- (size_type n) const
 
iterator & operator-= (size_type n)
 
Val * operator-> () const
 
bool operator== (iterator other) const
 
std::pair< const Key, Val > & pair () const
 
Val & value () const
 

Friends

class QMultiHash< Key, Val, Hash, KeyEqual >
 

Detailed Description

template<typename Key, typename Val, typename Hash, typename KeyEqual>
class QMultiHash< Key, Val, Hash, KeyEqual >::iterator

The QMultiHash::iterator class provides an STL style non-const iterator for QMultiHash. QMultiHash features both STL style iterators and Java style iterators.

After construction you must initialize the iterator using a method like QMultiHash::constBegin(), QMultiHash::constEnd(), or QMultiHash::find() before you can start iterating. The following is an example which prints all of the (key, value) pairs in the container.

hash.insert("January", 1);
hash.insert("February", 2);
...
hash.insert("December", 12);
for (auto iter = hash.constBegin(); iter != hash.constEnd(); ++iter) {
cout << iter.key() << ": " << iter.value() << endl;
}

Unlike QMap which orders its items by key, QHash stores its items in an arbitrary order. The only guarantee is items which share the same key will appear consecutively.

The following is an example which increments every value stored in the QHash by 2:

for (iter = hash.begin(); iter != hash.end(); ++iter) {
iter.value() += 2;
}

Here is an example which removes all of the items whose key is a string starting with an underscore character.

while (iter != hash.end()) {
if (iter.key().startsWith("_")) {
iter = hash.erase(iter);
} else {
++iter;
}
}

The call to QMultiHash::erase() removes the item pointed to by the iterator from the hash and returns an iterator to the next item. Here is another way of removing an item while iterating:

while (iter != hash.end()) {
++iter;
if (prev.key().startsWith("_")) {
hash.erase(prev);
}
}

It might be tempting to write code like the following. This code will potentially crash in ++iter, because iter is invalid after the call to erase().

// INCORRECT
while (i != hash.end()) {
if (i.key().startsWith("_")) {
hash.erase(i);
}
++i;
}
See also
QMultiHash::const_iterator

Member Typedef Documentation

template<typename Key , typename Val , typename Hash , typename KeyEqual >
QMultiHash< Key, Val, Hash, KeyEqual >::iterator::iterator_category

A synonym for std::bidirectional_iterator_tag indicating this iterator is a bidirectional iterator.

template<typename Key , typename Val , typename Hash , typename KeyEqual >
QMultiHash< Key, Val, Hash, KeyEqual >::iterator::pointer

A synonym for value_type *.

template<typename Key , typename Val , typename Hash , typename KeyEqual >
QMultiHash< Key, Val, Hash, KeyEqual >::iterator::reference

A synonym for value_type &.

template<typename Key , typename Val , typename Hash , typename KeyEqual >
QMultiHash< Key, Val, Hash, KeyEqual >::iterator::size_type

A synonym for the native size type of this container.

Constructor & Destructor Documentation

template<typename Key , typename Val , typename Hash , typename KeyEqual >
QMultiHash< Key, Val, Hash, KeyEqual >::iterator::iterator ( )
default

Constructs an uninitialized iterator.

Methods like key(), value(), and operator++() must not be called on an uninitialized iterator. Use operator=() to assign a value to it before using it.

See also
QMultiHash::begin(), QMultiHash::end()

Method Documentation

template<typename Key , typename Val , typename Hash , typename KeyEqual >
const Key & QMultiHash< Key, Val, Hash, KeyEqual >::iterator::key ( ) const
inline

Returns the current item's key as a const reference.

There is no direct way of changing an item's key through an iterator, although it can be done by calling QMultiHash::erase() followed by QMultiHash::insert() or QMultiHash::insertMulti().

See also
value()
template<typename Key , typename Val , typename Hash , typename KeyEqual >
bool QMultiHash< Key, Val, Hash, KeyEqual >::iterator::operator!= ( iterator  other) const
inline

Returns true if other points to a different item than this iterator, otherwise it returns false.

See also
operator==()
template<typename Key , typename Val , typename Hash , typename KeyEqual >
Val & QMultiHash< Key, Val, Hash, KeyEqual >::iterator::operator* ( ) const
inline

Equivalent to calling value().

See also
key()
template<typename Key , typename Val , typename Hash , typename KeyEqual >
iterator QMultiHash< Key, Val, Hash, KeyEqual >::iterator::operator+ ( size_type  n) const
inline

Returns an iterator to the item at n positions forward from this iterator. If n is negative the iterator goes backward.

This operation can be slow for large values of n.

See also
operator-()
template<typename Key , typename Val , typename Hash , typename KeyEqual >
iterator & QMultiHash< Key, Val, Hash, KeyEqual >::iterator::operator++ ( )
inline

The prefix ++ operator (++i) advances the iterator to the next item in the hash and returns an iterator to the new current item.

Calling this method on QMultiHash::end() leads to undefined behavior.

template<typename Key , typename Val , typename Hash , typename KeyEqual >
iterator QMultiHash< Key, Val, Hash, KeyEqual >::iterator::operator++ ( int  )
inline

The postfix ++ operator (i++) advances the iterator to the next item in the hash and returns an iterator to the previously current item.

template<typename Key , typename Val , typename Hash , typename KeyEqual >
iterator & QMultiHash< Key, Val, Hash, KeyEqual >::iterator::operator+= ( size_type  n)
inline

Advances the iterator by n items. If n is negative the iterator goes backward.

See also
operator-=(), operator+()
template<typename Key , typename Val , typename Hash , typename KeyEqual >
iterator QMultiHash< Key, Val, Hash, KeyEqual >::iterator::operator- ( size_type  n) const
inline

Returns an iterator to the item at n positions backward from this iterator. If n is negative the iterator goes forward.

This operation can be slow or large values of n.

See also
operator+()
template<typename Key , typename Val , typename Hash , typename KeyEqual >
iterator & QMultiHash< Key, Val, Hash, KeyEqual >::iterator::operator-= ( size_type  n)
inline

Makes the iterator go back by n items. If n is negative the iterator goes forward.

See also
operator+=(), operator-()
template<typename Key , typename Val , typename Hash , typename KeyEqual >
Val * QMultiHash< Key, Val, Hash, KeyEqual >::iterator::operator-> ( ) const
inline

Returns a pointer to the current item's value.

See also
value()
template<typename Key , typename Val , typename Hash , typename KeyEqual >
bool QMultiHash< Key, Val, Hash, KeyEqual >::iterator::operator== ( iterator  other) const
inline

Returns true if other points to the same item as this iterator, otherwise it returns false.

See also
operator!=()
template<typename Key , typename Val , typename Hash , typename KeyEqual >
std::pair< const Key, Val > & QMultiHash< Key, Val, Hash, KeyEqual >::iterator::pair ( ) const
inline

Returns the current item's key and value as a pair.

template<typename Key , typename Val , typename Hash , typename KeyEqual >
Val & QMultiHash< Key, Val, Hash, KeyEqual >::iterator::value ( ) const
inline

Returns a reference to the value for the current item. You can change the value of an item by using value() on the left side of an assignment.

if (i.key() == "Hello") {
i.value() = "Bonjour";
}
See also
key(), operator*()