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Object-Oriented Programming

(OOP)

Lecture No. 42

Iterator Operations

Input Iterators

• *p
  • Dereference operator (used as rvalue)
• p1 = p
  • Assignment
• p1 == p
  • Equality operator
• p1 != p
  • Inequality operator
• p->
  • Access Operator

Output Iterators

• *p
  • Dereference operator (can be used as lvalue)
• p1 = p
  • Assignment

Bidirectional Iterators

• Besides the operations of forward iterators

they also support

• --p
  • Pre-increment operator
• p--
  • post-decrement operator

Random-access Iterators

• Besides the operations of bidirectional

iterators, they also support

• p + i
  • Result is an iterator pointing at p + i
• p – i
  • Result is an iterator pointing at p – i

…Random-access Iterators

• p1 <= p
  • Returns true if p1 is before p2 in the container or p1 is equal to p
• p1 > p
  • Returns true if p1 is after p2 in the container
• p1 >= p
  • Returns true if p1 is after p2 in the container or p1 is equal to p

Example – Random Access Iterator

typedef std::vector< int > IntVector;

int main() {

const int SIZE = 3; int iArray[ SIZE ] = { 1, 2, 3 }; IntVector iv(iArray, iArray + SIZE); IntVector::iterator it = iv.begin(); cout << “Vector contents: ”; for ( int i = 0; i < SIZE; ++i ) cout << it[i] << ", "; return 0;

}

Example – Bidirectional Iterator

typedef std::set< int > IntSet;

int main() {

const int SIZE = 3; int iArray[ SIZE ] = { 1, 2, 3 }; IntSet is( iArray, iArray + SIZE ); IntSet::iterator it = is.begin(); cout << “Set contents: ”; for (int i = 0; i < SIZE; ++i) cout << it[i] << ", "; // Error return 0;

}

…Example – Bidirectional Iterator

typedef std::set< int > IntSet;

int main() {

const int SIZE = 3; int iArray[ SIZE ] = { 1, 2, 3 }; IntSet is( iArray, iArray + SIZE ); IntSet::iterator it = is.begin(); cout << “Set contents: ”; for ( int i = 0; i < SIZE; ++i ) cout << *it++ << ", "; // OK return 0;

}

…Example – Bidirectional Iterator

typedef std::set< int > IntSet;

int main() {

const int SIZE = 3; int iArray[ SIZE ] = { 1, 2, 3 }; IntSet is( iArray, iArray + SIZE ); IntSet::iterator it = is.end(); cout << “Set contents: ”; for (int i = 0; i < SIZE; ++i) cout << *--it << ", "; return 0;

}

…Sample Output

Set contents: 3, 2, 1,

…Example – Input Iterator

std::istream_iterator< int > inputIt( cin ); x = *inputIt++; y = *inputIt++; z = *inputIt; cout << "x = " << x << endl; cout << "y = " << y << endl; cout << "z = " << z << endl; return 0;

}

…Example – Input Iterator

int main() {

int x = 5; std::istream_iterator< int > inputIt( cin ); *inputIt = x; // Error return 0;

}