Download Understanding Cursors and Iterators in Object-Oriented Programming and more Slides Object Oriented Programming in PDF only on Docsity!
ObjectObject--Oriented ProgrammingOriented Programming
(OOP)(OOP)
Lecture No. 40 Lecture No. 40
CursorsCursors
► ► A better way is to useA better way is to use cursors cursors
► ► A cursor is a pointer that is declared outsideA cursor is a pointer that is declared outside
the container / aggregate object the container / aggregate object
► ► Aggregate object provides methods thatAggregate object provides methods that
help a cursor to traverse the elements help a cursor to traverse the elements
(^) T* first()T* first() (^) T* beyond()T* beyond() (^) T* next( T* )T* next( T* )
……VectorVector
template< class T > template< class T > T* Vector< T >::next( T* current ) T* Vector< T >::next( T* current )
{ { if ( current < (ptr + size) ) if ( current < (ptr + size) ) return ( current + 1 ); return ( current + 1 ); // else // else return current; return current; } }
Generic AlgorithmGeneric Algorithm
template< typename P, typename T > template< typename P, typename T > P find( P start, P beyond, P find( P start, P beyond, const T& x ) { const T& x ) { while ( start != beyond && while ( start != beyond && start != x )start != x ) ++start; ++start;
return start; return start; } }
ExampleExample^ – –^ ProblemProblem
int main() { int main() {
Set< int > is( 3 ); Set< int > is( 3 ); is.add( 10 ); is.add( 10 ); is.add( 20 ); is.add( 20 ); is.add( 30 ); is.add( 30 ); ET* first = iv.first(); ET* first = iv.first(); ET* beyond = iv.beyond(); ET* beyond = iv.beyond(); ET* found = find(first, beyond, 20); ET* found = find(first, beyond, 20); return 0; return 0;
} } docsity.com
Works FineWorks Fine
template< typename CT, typename ET > template< typename CT, typename ET > P find( CT& cont, const ET& x ) { P find( CT& cont, const ET& x ) { ET* start = cont.first(); ET* start = cont.first(); ET* beyond = cont.beyond(); ET* beyond = cont.beyond(); while ( start != beyond && while ( start != beyond && start != x )start != x ) start = cont.next( start ); start = cont.next( start ); return start; return start; } }
IteratorsIterators
► ► Iterator is an object that traverses aIterator is an object that traverses a
container without exposing its internal container without exposing its internal
representation representation
► ► Iterators are for containers exactly likeIterators are for containers exactly like
pointers are for ordinary data structures pointers are for ordinary data structures
ExampleExample – – Generic IteratorGeneric Iterator
Iterator^ Container first() beyond() next() …
operator * operator ++ …
……Generic IteratorGeneric Iterator
template< class CT, class ET > template< class CT, class ET >
Iterator< CT, ET >::Iterator( Iterator< CT, ET >::Iterator( Iterator< CT, ET >& it ) { Iterator< CT, ET >& it ) { container = it.container; container = it.container; index = it.index; index = it.index;
} }
……Generic IteratorGeneric Iterator
template< class CT, class ET > template< class CT, class ET >
ET& Iterator< CT, ET >::operator *() ET& Iterator< CT, ET >::operator *()
{ {
return *index; return *index;
} }
IteratorsIterators – – ConclusionConclusion
► ► With iterators more than one traversal canWith iterators more than one traversal can
be pending on a single container be pending on a single container
► ► Iterators allow to change the traversalIterators allow to change the traversal
strategy without changing the aggregate strategy without changing the aggregate
object object
► ► They contribute towards data abstraction byThey contribute towards data abstraction by
emulating pointers emulating pointers docsity.com
