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MODULE 32

THE C++ STL ADVANCED ITERATOR PART 5

My Training Period: xx hours

The program examples for the member used functions compiled using VC++7.0 / .Net, win32 empty console mode application.  This is a continuation from the previous Module. Linux g++ compilation examples given at the end of this Module. The source code for this tutorial is available in C++ STL Iterator source code samples.

C++ STL iterators abilities that supposed to be acquired:

▪         Able to understand and use iterator template classes.

▪         Able to understand and use iterator adapters.

▪         Able to understand and use stream iterator.

▪         Able to understand and use the member functions available in the library.

What do we have in this page?

1. The insert_iterator::operator++

2. insert_iterator, operator++ program example

3. The insert_iterator::operator= prototype

4. The istream_iterator Template Class prototype

5. The istream_iterator::char_type

6. The istream_iterator::traits_type

7. istream_iterator, char_type and traits_type program example

8. The istream_iterator::istream_iterator

9. istream_iterator, istream_iterator program example

10. The istreambuf_iterator Template Class

11. The istreambuf_iterator Template Class Members

12. The istreambuf_iterator::char_type

13. istreambuf_iterator, char_type program example

14. The istreambuf_iterator::int_type

15. istreambuf_iterator, int_type program example

insert_iterator& operator++();

insert_iterator& operator++(int);

Output:

The insert_iterator::operator= prototype

• Assignment operator used to implement the output iterator expression such as *i = x.

insert_iterator& operator=(typename Container::const_reference _Val);

Parameter

• The return value is a reference to the element inserted into the container.

• The member function evaluates Iter = container. insert(Iter, _Val), then returns *this pointer

// insert_iterator, operator= the assignment

#include <iterator>

#include <list>

#include <iostream>

using namespace std;

int main()

{

    int i;

    list<int>::iterator lstiter;

    list<int> lst;

    for(i = 10; i<=15; ++i)

        lst.push_back(i);

    cout<<"The list lst data: ";

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

        cout<<*lstiter<<" ";

    cout<<endl;

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

    *Iter = 12;

    *Iter = 7;

    *Iter = 33;

    *Iter = 24;

    cout<<"\nOperation: Iter(lst, lst.begin()) then *Iter = 12...\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:

The istream_iterator Template Class prototype

• Describes an input iterator object. It extracts objects of class Type from an input stream, which it accesses through an object it stores, of type pointer to basic_istream<CharType, Traits>.

template <

   class Type 

   class CharType = char

   class Traits = char_traits<CharType>

   class Distance= ptrdiff_t >

Parameters

• After constructing or incrementing an object of class istream_iterator with a non null stored pointer, the object attempts to extract and store an object of type Type from the associated input stream.

• If the extraction fails, the object effectively replaces the stored pointer with a null pointer, thus making an end-of-sequence indicator.

The istream_iterator Template Class Members

Typedefs

typedef CharType char_type;

typedef Traits traits_type;

// istream_iterator, char_type and traits_type

#include <iterator>

#include <vector>

#include <iostream>

using namespace std;

int main()

{

    typedef istream_iterator<int>::char_type chtype;

    typedef istream_iterator<int>::traits_type tratype;

    // standard iterator interface for reading elements from the input stream...

    cout<<"Enter integers separated by spaces & then\nany character e.g.: '3 4 7 T': ";

    // istream_iterator for reading int stream

    istream_iterator<int, chtype, tratype> intread(cin);

    // end-of-stream iterator

    istream_iterator<int, chtype, tratype> EOFintread;

    while(intread != EOFintread)

    {

        cout<<"Reading data:  "<<*intread<<endl;

        ++intread;

    }

    cout<<endl;

    return 0;

}

Output:

Member Functions

The istream_iterator::istream_iterator

• Constructs either an end-of-stream iterator as the default istream_iterator or a istream_iterator initialized to the iterator's stream type from which it reads. The constructor prototypes are:

1. istream_iterator();

2. istream_iterator(istream_type& _Istr);

Parameter

• The first constructor initializes the input stream pointer with a null pointer and creates an end-of-stream iterator.

• The second constructor initializes the input stream pointer with &_Istr, then attempts to extract and store an object of type Type.

• The end-of-stream iterator can be use to test whether an istream_iterator has reached the end of a stream.

// istream_iterator, istream_iterator

#include <iterator>

#include <vector>

#include <algorithm>

#include <iostream>

using namespace std;

int main()

{

    // used in conjunction with copy algorithm to put elements into a vector read from cin

    vector<int> vec(5);

    vector<int>::iterator Iter;

    cout<<"Enter 5 integers separated by spaces & then\na character e.g: '4 6 2 7 11 R': ";

    istream_iterator<int> intvecread(cin);

    // default constructor will test equal to end of stream for delimiting source range of vector

    copy(intvecread, istream_iterator<int>(), vec.begin());

    cin.clear();

    cout<<"vec data: ";

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

        cout<<*Iter<<" ";

    cout<<endl;

    return 0;

}

Output:

Operators

The istreambuf_iterator Template Class

• The template class istreambuf_iterator describes an input iterator object that extracts character elements from an input stream buffer, which it accesses through an object it stores, of type pointer to basic_streambuf<CharType, Traits>.

template < class CharType class Traits = char_traits<CharType> > 

Parameters

• The ostreambuf_iterator class must satisfy the requirements for an input iterator.

• After constructing or incrementing an object of class istreambuf_iterator with a non-null stored pointer, the object effectively attempts to extract and store an object of type CharType from the associated input stream.

• The extraction may be delayed, however, until the object is actually dereferenced or copied.  If the extraction fails, the object effectively replaces the stored pointer with a null pointer, thus making an end-of-sequence indicator.

The istreambuf_iterator Template Class Members

Typedefs

The istreambuf_iterator::char_type

• A type that provides for the character type of the ostreambuf_iterator.

typedef CharType char_type;

• The type is a synonym for the template parameter CharType.

// istreambuf_iterator, char_type

#include <iterator>

#include <vector>

#include <iostream>

#include <algorithm>

using namespace std;

int main()

{

    typedef istreambuf_iterator<char>::char_type chatype;

    typedef istreambuf_iterator<char>::traits_type tratype;

    cout<<"Enter line of text, then press Return key to \n"

            <<"insert into the output, & use a ctrl-Z Enter key\ncombination to exit: ";

    // istreambuf_iterator for input stream

    istreambuf_iterator< chatype, tratype> charInBuf(cin);

    ostreambuf_iterator<char> charOut(cout);

    // used in conjunction with replace_copy algorithm to insert into output stream and replaces spaces with hash sign

    replace_copy(charInBuf, istreambuf_iterator<char>(), charOut, ' ', '#');

    return 0;

}

Output:

The istreambuf_iterator::int_type

• A type that provides an integer type for an istreambuf_iterator.

typedef typename Traits::int_type int_type;

• The type is a synonym for Traits::int_type.

// istreambuf_iterator, int_type

#include <iterator>

#include <iostream>

using namespace std;

int main()

{

    cout<<"Operation: int_type intype = 77\n";

    istreambuf_iterator<char>::int_type intype = 77;

    cout<<"The int_type type = "<<intype<<endl;

    return 0;

}

Output:

tenouk C++ STL tutorial

Further C++ STL iterators related reading:

1. C++ Templates programming tutorials.

2. The source code for this tutorial is available in C++ STL Iterator source code samples.

3. A complete C & C++ Standard Library documentation that includes STL.

4. Check the best selling C / C++ and STL books at Amazon.com.

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