Detailed Description
The QSet::const_iterator class provides an STL-style 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<Key, T>::const_iterator allows you to iterate over a QSet. If you want to modify the QSet as you iterate over it, you must use QSet::iterator instead. 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.
The default QSet::const_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>::const_iterator i;
for (i = set.begin(); i != set.end(); ++i)
qDebug() << *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.constEnd())
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
const_iterator::const_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().
const_iterator::const_iterator ( const const_iterator & other )
Constructs a copy of other.
const_iterator::const_iterator ( const iterator & other )
This is an overloaded function.
Constructs a copy of other.
This function was introduced in Qt 4.2.
bool const_iterator::operator!= ( const const_iterator & other ) const
Returns true if other points to a different item than this iterator; otherwise returns false.
See also operator==().
const T & const_iterator::operator* () const
Returns a reference to the current item.
See also operator->().
const_iterator const_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-().
const_iterator & const_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--().
const_iterator const_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.
const_iterator & const_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+().
const_iterator const_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+().
const_iterator & const_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++().
const_iterator const_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.
const_iterator & const_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 * const_iterator::operator-> () const
Returns a pointer to the current item.
See also operator*().
const_iterator & const_iterator::operator= ( const const_iterator & other )
Assigns other to this iterator.
bool const_iterator::operator== ( const const_iterator & other ) const
Returns true if other points to the same item as this iterator; otherwise returns false.
See also operator!=().
