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MODULE 32_1

THE C++ STL ADVANCED ITERATOR PART 6

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 istream_iterator::traits_type

2. The istreambuf_iterator::equal

3. istreambuf_iterator, equal program example

4. The istreambuf_iterator::istreambuf_iterator

5. istreambuf_iterator, istreambuf_iterator program example

6. The istreambuf_iterator::operator++

7. The ostream_iterator Template Class

8. The ostream_iterator Template Class Members

9. The ostream_iterator::ostream_iterator

10. ostream_iterator, ostream_iterator program example

11. The ostream_iterator::operator=

12. ostream_iterator, operator= program example

13. The ostreambuf_iterator Template Class

14. The ostreambuf_iterator Template Class Members

15. The ostreambuf_iterator::ostreambuf_iterator

16. ostreambuf_iterator, ostreambuf_iterator program example

17. The ostreambuf_iterator::failed

18. ostreambuf_iterator, failed() program example

typedef Traits traits_type;

bool equal(const istreambuf_iterator& _Right) const;

// istreambuf_iterator, equal

#include <iterator>

#include <iostream>

using namespace std;

int main()

{

    cout<<"\nOperation: bol = readchinpt1.equal(readchinpt2)\n";

    cout<<"Enter a line of text then an Enter key to\ninsert into the output:\n";

    istreambuf_iterator<char> readchinpt1(cin);

    istreambuf_iterator<char> readchinpt2(cin);

    bool bol = readchinpt1.equal(readchinpt2);

    if(bol)

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

    else

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

    return 0;

}

Output:

The istreambuf_iterator::istreambuf_iterator

• Constructs an istreambuf_iterator that is initialized to read characters from the input stream.

1. istreambuf_iterator ( streambuf_type* _Strbuf = 0 ) throw();

2. istreambuf_iterator ( istream_type& _Istr ) throw();

Parameters

• The first constructor initializes the input stream-buffer pointer with _Strbuf.

• The second constructor initializes the input stream-buffer pointer with _Istr.rdbuf, and then eventually attempts to extract and store an object of type CharType.

// istreambuf_iterator, istreambuf_iterator

#include <iterator>

#include <vector>

#include <algorithm>

#include <iostream>

using namespace std;

int main()

{

	istreambuf_iterator<char>::istream_type &istrm = cin;

	istreambuf_iterator<char>::streambuf_type *strmbf = cin.rdbuf();

	cout<<"Enter a line of text, then an Enter key to insert into\n"

		<<"the output, (& use a ctrl-Z Enter key combination to exit):\n";

	istreambuf_iterator<char> charReadIn(cin);

	ostreambuf_iterator<char> charOut(cout);

	// used in conjunction with replace_copy algorithm to insert into output stream and replace spaces with hyphen-separators

	replace_copy(charReadIn, istreambuf_iterator<char>(), charOut, ' ', '-');

	return 0;

}

Output:

Operators

The istreambuf_iterator::operator++

• Either returns the next character from the input stream or copies the object before incrementing it and returns the copy.

istreambuf_iterator& operator++();

istreambuf_iterator operator++(int);

• The return value is an istreambut_iterator or a reference to an istreambuf_iterator.

• The first operator eventually attempts to extract and store an object of type CharType from the associated input stream.

• The second operator makes a copy of the object, increments the object, and then returns the copy.

// istreambuf_iterator, operator++

#include <iterator>

#include <iostream>

using namespace std;

int main()

{

    cout<<"Type a line of text & enter to output it, with stream\n"

            <<"buffer iterators, repeat as many times as desired,\n"

            <<"then keystroke ctrl-Z Enter to exit program: \n";

    istreambuf_iterator<char> inpos(cin);

    istreambuf_iterator<char> endpos;

    ostreambuf_iterator<char> outpos(cout);

    while(inpos != endpos)

    {

        *outpos = *inpos;

        // increment istreambuf_iterator

        ++inpos;

        ++outpos;

    }

    return 0;

}

Output:

The ostream_iterator Template Class

• The template class ostream_iterator describes an output iterator object that writes successive elements onto the output stream with the extraction operator >>.

template <

   class Type

   class CharType = char

   class Traits = char_traits<CharType> > 

Parameters

• The ostream_iterator class must satisfy the requirements for an output iterator.

• Algorithms can be written directly to output streams using an ostream_iterator.

The ostream_iterator Template Class Members

Typedefs

// ostream_iterator, ostream_iterator

#include <iterator>

#include <vector>

#include <iostream>

using namespace std;

int main()

{

    // ostream_iterator for stream cout

    ostream_iterator<int> intOut(cout, "\n");

    *intOut = 12;

    intOut++;

    *intOut = 33;

    intOut++;

    int i;

    vector<int> vec;

    for(i = 10; i<=15; ++i)

        vec.push_back(i);

    cout<<"Operation: with and without delimiter...\n";

    // write elements to standard output stream

    cout<<"Elements output without delimiter: ";

    copy(vec.begin(), vec.end(), ostream_iterator<int> (cout));

    cout<<endl;

    // write elements with delimiter " " to output stream

    cout<<"Elements output with delimiter: ";

    copy(vec.begin(), vec.end(), ostream_iterator<int> (cout, " "));

    cout<<endl;

    return 0;

}

Output:

Member Functions

Operators

The ostream_iterator::operator=

• Assignment operator used to implement the output_iterator expression such as *i = x for writing to an output stream.

ostream_iterator<Type, CharType, Traits>& operator=(const Type& _Val);

Parameter

• The return value is the operator inserts _Val into the output stream associated with the object, and then returns a reference to the ostream_iterator.

• The requirements for an output iterator that the ostream_iterator must satisfy require only the expression such as *j = x to be valid and says nothing about the operator or the operator= on their own.

• This member operator returns *this pointer.

// ostream_iterator, operator=

#include <iterator>

#include <vector>

#include <iostream>

using namespace std;

int main()

{

    // ostream_iterator for stream cout with new line delimiter

    ostream_iterator<int> intOut(cout, "\n");

    // standard iterator interface for writing elements to the output stream

    cout<<"Elements written to output stream:\n";

    *intOut = 12;

    *intOut = 21;

    // no effect on iterator position

    intOut++;

    *intOut = 9;

    *intOut = 7;

    return 0;

}

Output:

--------------------------------------------------------------------

The ostreambuf_iterator Template Class

• The template class ostreambuf_iterator describes an output iterator object that writes successive character elements onto the output stream with the extraction operator >>.

• The ostreambuf_iterators differ from those of the ostream_iterator Class in having characters instead of a generic type at the type of object being inserted into the output stream.

template < 

   class CharType = char

   class Traits = char_traits<CharType> > 

Parameters

• The ostreambuf_iterator class must satisfy the requirements for an output iterator. Algorithms can be written directly to output streams using an ostreambuf_iterator.

• The class provides a low-level stream iterator that allows access to the raw (unformatted) I/O stream in the form of characters and the ability to bypass the buffering and character translations associated with the high-level stream iterators.

The ostreambuf_iterator Template Class Members

Typedefs

The ostreambuf_iterator::ostreambuf_iterator

• Constructs an ostreambuf_iterator that is initialized to write characters to the output stream.

1. ostreambuf_iterator(streambuf_type* _Strbuf) throw();

2. ostreambuf_iterator(ostream_type& _Ostr) throw();

Parameters

• The first constructor initializes the output stream-buffer pointer with _Strbuf.

• The second constructor initializes the output stream-buffer pointer with _Ostr.rdbuf.

• The stored pointer must not be a null pointer.

// ostreambuf_iterator, ostreambuf_iterator

#include <iterator>

#include <vector>

#include <iostream>

using namespace std;

int main()

{

    // ostreambuf_iterator for stream cout

    ostreambuf_iterator<char> charOut(cout);

    *charOut = '7';

    charOut ++;

    *charOut  = 'T';

    charOut ++;  

    *charOut = 'W';

    cout<<" are characters output."<<endl;

    ostreambuf_iterator<char> strOut(cout);

    string str = "These characters are being written to the output stream.\n ";

    copy(str.begin(), str.end(), strOut);

    return 0;

}

Output:

Member Functions

The ostreambuf_iterator::failed

• Tests for failure of an insertion into the output stream buffer.

bool failed() const throw();

• The return value is true if no insertion into the output stream buffer has failed earlier; otherwise false.

• The member function returns true if, in any prior use of member operator=, the call to subf_→sputc returned eof.

// ostreambuf_iterator, failed()

#include <iterator>

#include <vector>

#include <iostream>

using namespace std;

int main()

{

    // ostreambuf_iterator for stream cout

    ostreambuf_iterator<char> charOut(cout);

    *charOut = 'T';

    charOut ++;

    *charOut  = '7';

    charOut ++;  

    *charOut = 'R';

    cout<<" are characters output"<<endl;

    bool bol = charOut.failed();

    if(bol)

        cout<<"At least one insertion failed."<<endl;

    else

        cout<<"No insertions failed."<<endl;

    return 0;

}

Output:

Operators

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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