std::istreambuf_iterator

template< class CharT, class Traits = std::char_traits<CharT> >
class istreambuf_iterator : public std::iterator< std::input_iterator_tag,
                                                  CharT,
                                                  typename Traits::off_type,
                                                  /* unspecified, usually CharT* */,
                                                  CharT >

template< class CharT, class Traits = std::char_traits<CharT> >
class istreambuf_iterator;

std::istreambuf_iterator is a single-pass input iterator that reads successive characters from the std::basic_streambuf object for which it was constructed. The actual read operation is performed when the iterator is incremented, not when it is dereferenced. The first character may be read when the iterator is constructed or when the first dereferencing is done. Otherwise, dereferencing only returns a copy of the most recently read character.

The default-constructed std::istreambuf_iterator is known as the end-of-stream iterator. When a valid std::istreambuf_iterator reaches the end of the underlying stream, it becomes equal to the end-of-stream iterator. Dereferencing or incrementing it further invokes undefined behavior.

std::istreambuf_iterator has a trivial copy constructor, a constexpr default constructor, and a trivial destructor.

Member types

Member functions

Non-member functions

Member types

Note: before C++17, these member types are required to be obtained by inheriting from std::iterator<std::input_iterator_tag,CharT,Traits::off_type,/* unspecified, usually CharT* */,CharT>.

Example

#include <vector>
#include <sstream>
#include <iostream>
#include <iterator>
 
int main()
{
    // typical use case: an input stream represented as a pair of iterators
    std::istringstream in("Hello, world");
    std::vector<char> v( (std::istreambuf_iterator<char>(in)),
                          std::istreambuf_iterator<char>() );
    std::cout << "v has " << v.size() << " bytes. ";
    v.push_back('\0');
    std::cout << "it holds \"" << &v[0] << "\"\n";
 
 
    // demonstration of the single-pass nature
    std::istringstream s("abc");
    std::istreambuf_iterator<char> i1(s), i2(s);
    std::cout << "i1 returns " << *i1 << '\n'
              << "i2 returns " << *i2 << '\n';
    ++i1;
    std::cout << "after incrementing i1, but not i2\n"
              << "i1 returns " << *i1 << '\n'
              << "i2 returns " << *i2 << '\n';
    ++i2; // this makes the apparent value of *i2 to jump from 'a' to 'c'
    std::cout << "after incrementing i2, but not i1\n"
              << "i1 returns " << *i1 << '\n'
              << "i2 returns " << *i2 << '\n';
 
}

v has 12 bytes. it holds "Hello, world"
i1 returns a
i2 returns a
after incrementing i1, but not i2
i1 returns b
i2 returns a
after incrementing i2, but not i1
i1 returns b
i2 returns c

See also