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MODULE 31_1

THE C++ STL ITERATOR PART 2

What do we have in this session?

1. back_inserter() prototype

2. iterator, back_inserter() example

3. distance() prototype

4. iterator, distance() example

5. front_inserter() prototype

6. iterator, front_inserter() example

7. inserter() prototype

8. operator!= prototypes

9. iterator, operator== example

10. operator< prototype

11. iterator, operator< example

template<class Container>

   back_insert_iterator<Container> back_inserter( Container& _Cont );

distance() prototype

template<class InputIterator>

   typename iterator_traits<InputIterator>::difference_type

      distance( InputIterator _First, InputIterator _Last );

Parameters

• The return value is the number of times that _First must be incremented until it equal _Last.

• The advance function has constant complexity when InputIterator satisfies the requirements for a random-access iterator; otherwise, it has linear complexity and so is potentially expensive.

// iterator, distance()

#include <iterator>

#include <list>

#include <iostream>

using namespace std;

int main()

{

    int i;

    list<int> lst;

    for(i = -1; i < 10; ++i)

        lst.push_back(2*i);

    list <int>::iterator lstiter, lstpos = lst.begin();

    cout<<"The list lst data: ";

    for(lstiter = lst.begin(); lstiter != lst.end(); lstiter++)

        cout<<*lstiter<<" ";

    cout<<endl;

    cout<<"\nOperation: lstpos = lst.begin()\n";

    cout<<"The first element pointed by iterator lstpos: "<<*lstpos<<endl;

    cout<<"\nOperation: advance(lstpos, 5)\n";

    advance(lstpos, 5);

    cout<<"lstpos is advanced 5 steps forward to point to: "<<*lstpos<<endl;

    list<int>::difference_type lstdiff;

    cout<<"\nOperation: lstdiff = distance(lst.begin(), lstpos)\n";

    lstdiff = distance(lst.begin(), lstpos);

    cout<<"The distance from lst.begin() to lstpos is: "<<lstdiff<<" elements"<<endl;

    return 0;

}

Output

front_inserter() prototype

template<class Container>front_insert_iterator<Container> front_inserter( Container& _Cont );

Parameter

• The return value is a front_insert_iterator() associated with the container object _Cont.

• The member function front_insert_iterator() of the front_insert_iterator class may also be used.

• Within the STL, the argument must refer to one of the two sequence containers that have the member function push_back():deque class or list class.

// iterator, front_inserter()

#include <iterator>

#include <list>

#include <iostream>

using namespace std;

int main()

{

    int i;

    list<int>::iterator lstiter;

    list<int> lst;

    for(i = -2; i<=5; ++i)

        lst.push_back(i);

    cout<<"The list lst data: ";

    for(lstiter = lst.begin(); lstiter != lst.end(); lstiter++)

        cout<<*lstiter<<" ";

    cout<<endl;

    // using the template function to insert an element

    cout<<"\nOperation: ++Iter then *Iter = 12...\n";

    front_insert_iterator< list < int> > Iter(lst);

    *Iter = 21;

    ++Iter;

    *Iter = 12;

    cout<<"New list lst data: ";

    for(lstiter = lst.begin(); lstiter != lst.end(); lstiter++)

        cout<<*lstiter<<" ";

    cout<<endl;

    cout<<"\nOperation: front_inserter(lst) = 23...\n";

    // alternatively, using the front_insert() member function

    front_inserter(lst) = 23;

    front_inserter(lst) = 9;

    cout<<"New list lst data: ";

    for(lstiter = lst.begin(); lstiter != lst.end(); lstiter++)

        cout<<*lstiter<<" ";

    cout<<endl;

    return 0;

}

Output:

template<class Container, class Iterator>

   insert_iterator<Container> inserter( Container& _Cont, Iterator _It );

// iterator, inserter()

#include <iterator>

#include <list>

#include <iostream>

using namespace std;

int main()

{

    int i;

    list <int>::iterator lstiter;

    list<int> lst;

    for(i = -3; i<=2; ++i)

        lst.push_back(i);

    cout<<"The list lst data: ";

    for(lstiter = lst.begin(); lstiter != lst.end(); lstiter++)

        cout<<*lstiter<<" ";

    cout<<endl;

    // using the template version to insert an element

    insert_iterator<list <int> > Iter(lst, lst.begin());

    *Iter = 7;

    ++Iter;

    *Iter = 12;

    cout<<"\nOperation: *Iter = 7 then ++Iter...\n";

    cout<<"After the insertions, the list lst data: \n";

    for(lstiter = lst.begin(); lstiter != lst.end(); lstiter++)

        cout<<*lstiter<<" ";

    cout<<endl;

    // alternatively, using the member function inserter() to insert an element

    inserter(lst, lst.end()) = 31;

    inserter(lst, lst.end()) = 42;

    cout<<"\nOperation: inserter(lst, lst.end()) = 42...\n";

    cout<<"After the insertions, the list lst data: \n";

    for(lstiter = lst.begin(); lstiter != lst.end(); lstiter++)

        cout<<*lstiter<<" ";

    cout<<endl;

    return 0;

}

Output:

Operators

operator!= prototypes

1. template<class RandomIterator>bool operator!=( const reverse_iterator<RandomIterator>& _Left, const reverse_iterator<RandomIterator>& _Right );

2. template<class Type, class CharType, class Traits, class Distance>bool operator!=( const istream_iterator<Type, CharType, Traits, Distance>& _Left, const istream_iterator<Type, CharType, Traits, Distance>& _Right );

3. template<class CharType, class Tr>bool operator!=( const istreambuf_iterator<CharType, Traits>& _Left, const istreambuf_iterator<CharType, Traits>& _Right );

Parameters

• The return value is true if the iterator objects are not equal; false if the iterator objects are equal.

• One iterator object is equal to another if they address the same elements in a container. If two iterators point to different elements in a container, then they are not equal.

// iterator, operator!=

#include <iterator>

#include <vector>

#include <iostream>

using namespace std;

int main()

{

    int i;

    vector<int> vec;

    for(i = 1; i<=10; ++i) 

        vec.push_back(i);

    vector<int>::iterator veciter;

    cout<<"The vector vec data: ";

    for(veciter = vec.begin(); veciter != vec.end(); veciter++)

        cout<<*veciter<<" ";

    cout<<endl;

    // initializing reverse_iterators to the last element

    vector<int>::reverse_iterator rvecpos1 = vec.rbegin(), rvecpos2 = vec.rbegin();

    cout<<"The iterators rvecpos1 and rvecpos2 points to the first\n"

            <<"element in the reversed sequence: "<<*rvecpos1<<endl;

    cout<<"\nOperation: rvecpos1 != rvecpos2\n";

    if(rvecpos1 != rvecpos2)

        cout<<"The iterators are not equal."<<endl;

    else

        cout<<"The iterators are equal."<<endl;

    rvecpos1++;

    cout<<"\nThe iterator rvecpos1 now points to the second\nelement in the reversed sequence: "<<*rvecpos1<<endl;

    cout<<"\nOperation: rvecpos1 != rvecpos2\n";

    if(rvecpos1 != rvecpos2)

        cout<<"The iterators are not equal."<<endl;

    else

        cout<<"The iterators are equal."<<endl;

    return 0;

}

Output:

operator== example

• The return value is true if the iterator objects are equal; false if the iterator objects are not equal.

• One iterator object is equal to another if they address the same elements in a container. If two iterators point to different elements in a container, then they are not equal.

// iterator, operator==

#include <iterator>

#include <vector>

#include <iostream>

using namespace std;

int main()

{

    int i;

    vector<int> vec;

    for(i = 11; i<15; ++i)

        vec.push_back(i);

    vector <int>::iterator veciter;

    cout<<"The vector vec data: ";

    for(veciter = vec.begin(); veciter != vec.end(); veciter++)

        cout<<*veciter<<" ";

    cout<<endl;

    // initializing reverse_iterators to the last element

    vector<int>::reverse_iterator rvecpos1 = vec.rbegin(), rvecpos2 = vec.rbegin();

    cout<<"\nThe iterators rvecpos1 and rvecpos2 points\nto the first"

        <<"element in the reversed sequence: "<<*rvecpos1<<endl;

    cout<<"\nOperation: rvecpos1 == rvecpos2\n";

    if(rvecpos1 == rvecpos2)

        cout<<"The iterators are equal."<<endl;

    else

        cout<<"The iterators are not equal."<<endl;

    rvecpos1++;

    cout<<"\nThe iterator rvecpos1 now points to the second\n"

        <<"element in the reversed sequence: "<<*rvecpos1<<endl;

    cout<<"\nOperation: rvecpos1 == rvecpos2\n";

    if(rvecpos1 == rvecpos2)

        cout<<"The iterators are equal."<<endl;

    else

        cout<<"The iterators are not equal."<<endl;

    return 0;

}

Output:

operator< prototype

template<class RandomIterator>

   bool operator<( const reverse_iterator<RandomIterator>& _Left, const reverse_iterator<RandomIterator>& _Right );

Parameters

• The return value is true if the iterator on the left side of the expression is less than the iterator on the right side of the expression; false if it is greater than or equal to the iterator on the right.

• One iterator object is less than another if it addresses an element that occurs earlier in the container than the element addressed by the other iterator object.

• One iterator object is not less than another if it addresses either the same element as the other iterator object or an element that occurs later in the container than the element addressed by the other iterator object.

// iterator, operator<

#include <iterator>

#include <vector>

#include <iostream>

int main()

{

    using namespace std;

    int i;

    vector<int> vec;

    for(i = 10; i<= 17; ++i)

        vec.push_back(i);

    vector<int>::iterator veciter;

    cout<<"The initial vector vec is: ";

    for(veciter = vec.begin(); veciter != vec.end(); veciter++)

        cout<<*veciter<<" ";

    cout<<endl;

    // initializing reverse_iterators to the last element

    vector<int>::reverse_iterator rvecpos1 = vec.rbegin(), rvecpos2 = vec.rbegin();

    cout<<"The iterators rvecpos1 & rvecpos2 initially point\nto the first element in the reversed sequence: "<<*rvecpos1<<endl;

    cout<<"\nOperation: rvecpos1 < rvecpos2\n";

    if(rvecpos1 < rvecpos2)

        cout<<"The iterator rvecpos1 is less than the iterator rvecpos2."<<endl;

    else

        cout<<"The iterator rvecpos1 is not less than the iterator rvecpos2."<<endl;

    cout<<"\nOperation: rvecpos1 > rvecpos2\n";

    if(rvecpos1 > rvecpos2)

        cout<<"The iterator rvecpos1 is greater than the iterator rvecpos2."<<endl;

    else

        cout<<"The iterator rvecpos1 is not greater than the iterator rvecpos2."<<endl;

    cout<<"\nOperation: rvecpos2++;\n";

    rvecpos2++;

    cout<<"The iterator rvecpos2 now points to the second\nelement in the reversed sequence: "<<*rvecpos2<<endl;

    cout<<"\nOperation: rvecpos1 < rvecpos2\n";

    if(rvecpos1 < rvecpos2)

        cout<<"The iterator rvecpos1 is less than the iterator rvecpos2."<<endl;

    else

        cout<<"The iterator rvecpos1 is not less than the iterator rvecpos2."<<endl;

    cout<<"\nOperation: rvecpos1 > rvecpos2\n";

    if(rvecpos1 > rvecpos2)

        cout<<"The iterator rvecpos1 is greater than the iterator rvecpos2."<<endl;

    else

        cout<<"The iterator rvecpos1 is not greater than the iterator rvecpos2."<<endl;

    return 0;

}

Output:

tenouk C++ STL tutorial

Further C++ STL iterators related reading:

1. The source code in text for this tutorial is available inC++ STL Iterator source code.

2. Acomplete C Standard Library.

3. Acomplete C++ Standard Library documentation that includes STL.

4. C++ Templates programming tutorials.

5. Check thebest selling C / C++ and STL books at Amazon.com.

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