Detailed Description
The QSet::iterator class provides an STL-style non-const iterator for QSet.
QSet features both STL-style iterators and Java-style iterators. The STL-style iterators are more low-level and more cumbersome to use; on the other hand, they are slightly faster and, for developers who already know STL, have the advantage of familiarity.
QSet<T>::iterator allows you to iterate over a QSet and to remove items (using QSet::erase()) while you iterate. (QSet doesn't let you modify a value through an iterator, because that would potentially require moving the value in the internal hash table used by QSet.) If you want to iterate over a const QSet, you should use QSet::const_iterator. It is generally good practice to use QSet::const_iterator on a non-const QSet as well, unless you need to change the QSet through the iterator. Const iterators are slightly faster, and can improve code readability.
QSet<T>::iterator allows you to iterate over a QSet<T> and modify it as you go (using QSet::erase()). However,
The default QSet::iterator constructor creates an uninitialized iterator. You must initialize it using a function like QSet::begin(), QSet::end(), or QSet::insert() before you can start iterating. Here's a typical loop that prints all the items stored in a set:
QSet<QString> set;
set << "January" << "February" << ... << "December";
QSet<QString>::iterator i;
for (i = set.begin(); i != set.end(); ++i)
qDebug() << *i;
Here's a loop that removes certain items (all those that start with 'J') from a set while iterating:
QSet<QString> set;
set << "January" << "February" << ... << "December";
QSet<QString>::iterator i = set.begin();
while (i != set.end()) {
if ((*i).startsWith('J')) {
i = set.erase(i);
} else {
++i;
}
}
STL-style iterators can be used as arguments to generic algorithms. For example, here's how to find an item in the set using the qFind() algorithm:
QSet<QString> set;
...
QSet<QString>::iterator it = qFind(set.begin(), set.end(), "Jeanette");
if (it != set.end())
cout << "Found Jeanette" << endl;
Multiple iterators can be used on the same set. However, you may not attempt to modify the container while iterating on it.
Member Function Documentation
iterator::iterator()
Constructs an uninitialized iterator.
Functions like operator*() and operator++() should not be called on an uninitialized iterator. Use operator=() to assign a value to it before using it.
See also QSet::begin() and QSet::end().
iterator::iterator(const iterator & other)
Constructs a copy of other.
bool iterator::operator!=(const iterator & other) const
Returns true if other points to a different item than this iterator; otherwise returns false.
See also operator==().
bool iterator::operator!=(const const_iterator & other) const
This is an overloaded function.
const T & iterator::operator*() const
Returns a reference to the current item.
See also operator->().
iterator iterator::operator+(int j) const
Returns an iterator to the item at j positions forward from this iterator. (If j is negative, the iterator goes backward.)
This operation can be slow for large j values.
See also operator-().
iterator & iterator::operator++()
The prefix ++ operator (++it) advances the iterator to the next item in the set and returns an iterator to the new current item.
Calling this function on QSet::constEnd() leads to undefined results.
See also operator--().
iterator iterator::operator++(int)
This is an overloaded function.
The postfix ++ operator (it++) advances the iterator to the next item in the set and returns an iterator to the previously current item.
iterator & iterator::operator+=(int j)
Advances the iterator by j items. (If j is negative, the iterator goes backward.)
This operation can be slow for large j values.
See also operator-=() and operator+().
iterator iterator::operator-(int j) const
Returns an iterator to the item at j positions backward from this iterator. (If j is negative, the iterator goes forward.)
This operation can be slow for large j values.
See also operator+().
iterator & iterator::operator--()
The prefix -- operator (--it) makes the preceding item current and returns an iterator to the new current item.
Calling this function on QSet::begin() leads to undefined results.
See also operator++().
iterator iterator::operator--(int)
This is an overloaded function.
The postfix -- operator (it--) makes the preceding item current and returns an iterator to the previously current item.
iterator & iterator::operator-=(int j)
Makes the iterator go back by j items. (If j is negative, the iterator goes forward.)
This operation can be slow for large j values.
See also operator+=() and operator-().
const T * iterator::operator->() const
Returns a pointer to the current item.
See also operator*().
iterator & iterator::operator=(const iterator & other)
Assigns other to this iterator.
bool iterator::operator==(const iterator & other) const
Returns true if other points to the same item as this iterator; otherwise returns false.
See also operator!=().
bool iterator::operator==(const const_iterator & other) const
This is an overloaded function.
