istream_iterator Class

The latest version of this topic can be found at istream_iterator Class.

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>.

Syntax

template <class Type, class CharType = char, class Traits = char_traits<CharType>, class Distance = ptrdiff_t,>  
class istream_iterator
 : public iterator<
    input_iterator_tag, Type, Distance,
    const Type *,
    const Type&>;

Parameters

Type
The type of object to be extracted from the input stream.

CharType
The type that represents the character type for the istream_iterator. This argument is optional and the default value is char.

Traits
The type that represents the character type for the istream_iterator. This argument is optional and the default value is char_traits< CharType>.

Distance
A signed integral type that represents the difference type for the istream_iterator. This argument is optional and the default value is ptrdiff_t.

After constructing or incrementing an object of class istream_iterator with a nonnull 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.

Constructors

Typedefs

Operators

Requirements

Header: <iterator>

Namespace: std

istream_iterator::char_type

A type that provides for the character type of the istream_iterator.

typedef CharType char_type;

Remarks

The type is a synonym for the template parameter Chartype.

Example

// istream_iterator_char_type.cpp  
// compile with: /EHsc  
#include <iterator>  
#include <vector>  
#include <iostream>  
  
int main( )  
{  
   using namespace std;  
  
   typedef istream_iterator<int>::char_type CHT1;  
   typedef istream_iterator<int>::traits_type CHTR1;  
  
   // Standard iterator interface for reading  
   // elements from the input stream:  
   cout << "Enter integers separated by spaces & then\n"  
        << " any character ( try example: '2 4 f' ): ";  
  
   // istream_iterator for reading int stream  
   istream_iterator<int, CHT1, CHTR1> intRead ( cin );  
  
   // End-of-stream iterator  
   istream_iterator<int, CHT1, CHTR1> EOFintRead;  
  
   while ( intRead != EOFintRead )  
   {  
      cout << "Reading:  " << *intRead << endl;  
      ++intRead;  
   }  
   cout << endl;  
}  

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.

istream_iterator();

istream_iterator(istream_type& _Istr);

Parameters

_Istr
The input stream to be read use to initialize the istream_iterator.

Remarks

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.

Example

// istream_iterator_istream_iterator.cpp  
// compile with: /EHsc  
#include <iterator>  
#include <vector>  
#include <algorithm>  
#include <iostream>  
  
int main( )  
{  
   using namespace std;  
  
   // Used in conjunction with copy algorithm  
   // to put elements into a vector read from cin  
   vector<int> vec ( 4 );  
   vector <int>::iterator Iter;  
  
   cout << "Enter 4 integers separated by spaces & then\n"  
        << " a character ( try example: '2 4 6 8 a' ): ";  
   istream_iterator<int> intvecRead ( cin );  
  
   // Default constructor will test equal to end of stream  
   // for delimiting source range of vecor  
   copy ( intvecRead , istream_iterator<int>( ) , vec.begin ( ) );  
   cin.clear ( );  
  
   cout << "vec = ";  
   for ( Iter = vec.begin( ) ; Iter != vec.end( ) ; Iter++ )  
      cout << *Iter << " "; cout << endl;  
}  

istream_iterator::istream_type

A type that provides for the stream type of the istream_iterator.

typedef basic_istream<CharType, Traits> istream_type;

Remarks

The type is a synonym for basic_istream< CharType, Traits>.

Example

See istream_iterator for an example of how to declare and use istream_type.

istream_iterator::operator*

The dereferencing operator returns the stored object of type Type addressed by the istream_iterator.

const Type& operator*() const;

Return Value

The stored object of type Type.

Example

// istream_iterator_operator.cpp  
// compile with: /EHsc  
#include <iterator>  
#include <vector>  
#include <algorithm>  
#include <iostream>  
  
int main( )  
{  
   using namespace std;  
  
   cout << "Enter integers separated by spaces & then\n"  
        << " a character ( try example: '2 4 6 8 a' ): ";  
  
   // istream_iterator from stream cin  
   istream_iterator<int> intRead ( cin );  
  
   // End-of-stream iterator  
   istream_iterator<int> EOFintRead;  
  
   while ( intRead != EOFintRead )  
   {  
      cout << "Reading:  " << *intRead << endl;  
      ++intRead;  
   }  
   cout << endl;  
}  

istream_iterator::operator->

Returns the value of a member, if any.

const Type* operator->() const;

Return Value

The value of a member, if any.

Remarks

i -> is equivalent to (* i). m

The operator returns &**this.

Example

// istream_iterator_operator_vm.cpp  
// compile with: /EHsc  
#include <iterator>  
#include <iostream>  
#include <complex>  
  
using namespace std;  
  
int main( )  
{  
   cout << "Enter complex numbers separated by spaces & then\n"  
        << " a character pair ( try example: '(1,2) (3,4) (a,b)' ): ";  
  
   // istream_iterator from stream cin  
   istream_iterator< complex<double> > intRead ( cin );  
  
   // End-of-stream iterator  
   istream_iterator<complex<double> > EOFintRead;  
  
   while ( intRead != EOFintRead )  
   {  
      cout << "Reading the real part: " << intRead ->real( ) << endl;  
      cout << "Reading the imaginary part: " << intRead ->imag( ) << endl;  
      ++intRead;  
   }  
   cout << endl;  
}  

istream_iterator::operator++

Either extracts an incremented object from the input stream or copies the object before incrementing it and returns the copy.

istream_iterator<Type, CharType, Traits, Distance>& operator++();

istream_iterator<Type, CharType, Traits, Distance> operator++(int);

Return Value

The first member operator returns a reference to the incremented object of type Type extracted from the input stream and the second member function returns a copy of the object.

Example

// istream_iterator_operator_incr.cpp  
// compile with: /EHsc  
#include <iterator>  
#include <vector>  
#include <algorithm>  
#include <iostream>  
  
int main( )  
{  
   using namespace std;  
  
   cout << "Enter integers separated by spaces & then\n"  
        << " a character ( try example: '2 4 6 8 a' ): ";  
  
   // istream_iterator from stream cin  
   istream_iterator<int> intRead ( cin );  
  
   // End-of-stream iterator  
   istream_iterator<int> EOFintRead;  
  
   while ( intRead != EOFintRead )  
   {  
      cout << "Reading:  " << *intRead << endl;  
      ++intRead;  
   }  
   cout << endl;  
}  

istream_iterator::traits_type

A type that provides for the character traits type of the istream_iterator.

typedef Traits traits_type;

Remarks

The type is a synonym for the template parameter Traits.

Example

// istream_iterator_traits_type.cpp  
// compile with: /EHsc  
#include <iterator>  
#include <iostream>  
  
int main( )  
{  
   using namespace std;  
  
   typedef istream_iterator<int>::char_type CHT1;  
   typedef istream_iterator<int>::traits_type CHTR1;  
  
   // Standard iterator interface for reading  
   // elements from the input stream:  
   cout << "Enter integers separated by spaces & then\n"  
        << " any character ( try example: '10 20 a' ): ";  
  
   // istream_iterator for reading int stream  
   istream_iterator<int, CHT1, CHTR1> intRead ( cin );  
  
   // End-of-stream iterator  
   istream_iterator<int, CHT1, CHTR1> EOFintRead;  
  
   while ( intRead != EOFintRead )  
   {  
      cout << "Reading:  " << *intRead << endl;  
      ++intRead;  
   }  
   cout << endl;  
}  

See Also

input_iterator_tag Struct
iterator Struct
<iterator>
Thread Safety in the C++ Standard Library
Standard Template Library