Iterators
A stream iterator that has iterator capabilities for istreams. This iterator allows generic algorithms to be used directly on streams.
| Data Types | |
| char_type istream_type traits_type value_type |
| Member Functions |
| operator!=() operator*() operator++() operator->() operator==() |
#include <iterator>
template <class T, class charT, class traits = ios_traits<charT>,
class Distance = ptrdiff_t>
class istream_iterator : public iterator<input_iterator_tag,
T,Distance>;
Stream iterators are the standard iterator interface for input and output streams.
The class istream_iterator reads elements from an input stream using operator >>. A value of type T is retrieved and stored when the iterator is constructed and each time operator++ is called. The iterator is equal to the end-of-stream iterator value if the end-of-file is reached. You can use the constructor with no arguments to create an end-of-stream iterator. The only valid use of this iterator is to compare to other iterators when checking for end of file. Do not attempt to dereference the end-of-stream iterator; it plays the same role as the past-the-end iterator of the end() function of containers. Since an istream_iterator is an input iterator, you cannot assign to the value returned by dereferencing the iterator. This also means that istream_iterators can only be used for single pass algorithms.
Since a new value is read every time the operator++ is used on an istream_iterator, that operation is not equality-preserving. This means that i == j does not mean that ++i == ++j (although two end-of-stream iterators are always equal).
template <class T, class charT, class traits = ios_traits<charT>
class Distance = ptrdiff_t>
class istream_iterator :
public iterator<input_iterator_tag,T, Distance>
{
public:
typedef T value_type;
typedef charT char_type;
typedef traits traits_type;
typedef basic_istream<charT,traits> istream_type;
istream_iterator();
istream_iterator (istream_type&);
istream_iterator
(const stream_iterator<T,charT,traits,Distance>&);
~istream_itertor ();
const T& operator*() const;
const T* operator ->() const;
istream_iterator <T,charT,traits,
Distance>& operator++();
istream_iterator <T,charT,traits,Distance>
operator++ (int)
};
// Non-member Operators
template <class T, class charT, class traits,class Distance>
bool operator==(const istream_iterator<T,charT,traits,Distance>&,
const istream_iterator<T,charT,traits,Distance>&);
template <class T, class charT, class traits,class Distance>
bool operator!=(const istream_iterator<T,charT,traits,Distance>&,
const istream_iterator<T,charT,traits,Distance>&);
value_type;
Type of value to stream in.
char_type;
Type of character the stream is built on.
traits_type;
Traits used to build the stream.
istream_type;
Type of stream this iterator is constructed on.
istream_iterator();
Constructs an end-of-stream iterator. This iterator can be used to compare against an end-of-stream condition. Use it to provide end iterators to algorithms.
istream_iterator(istream& s);
Constructs an istream_iterator on the given stream.
istream_iterator(const istream_iterator& x);
Copy constructor.
~istream_iterator();
const T& operator*() const;
Returns the current value stored by the iterator.
const T* operator->() const;
Returns a pointer to the current value stored by the iterator.
istream_iterator& operator++() istream_iterator operator++(int)
Retrieves the next element from the input stream.
bool
operator==(const istream_iterator<T,charT,traits,
Distance>& x,
const
istream_iterator<T,charT,traits,Distance>& y)
Returns true if x is the same as y.
bool
operator!=(const istream_iterator<T,charT,traits,
Distance>& x,
const
istream_iterator<T,charT,traits,Distance>& y)
Returns true if x is not the same as y.
//
// io_iter.cpp
//
#include <iterator>
#include <vector>
#include <numeric>
#include <iostream>
using namespace std;
int main ()
{
vector<int> d;
int total = 0;
//
// Collect values from cin until end of file
// Note use of default constructor to get ending iterator
//
cout << "Enter a sequence of integers (eof to quit): " ;
copy(istream_iterator<int,char>(cin),
istream_iterator<int,char>(),
inserter(d,d.begin()));
//
// stream the whole vector and the sum to cout
//
copy(d.begin(),d.end()-1,
ostream_iterator<int,char>(cout," + "));
if (d.size())
cout << *(d.end()-1) << " = " <<
accumulate(d.begin(),d.end(),total) << endl;
return 0;
}
If your compiler does not support default template parameters, then you always need to supply the Allocator template argument. You also have to include all parameters to the istream_iterator template. For instance, you have to write:
vector<int, allocator<int> >
instead of:
vector<int>
If your compiler does not support namespaces, then you do not need the using declaration for std.