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std::istreambuf_iterator

Defined in header <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 >
 (until C++17) 
template< class CharT, class Traits = std::char_traits<CharT> >
class istreambuf_iterator;
 (since C++17)

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 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.

 (since C++11)

Member types

Member type Definition
iterator_category std::input_iterator_tag
value_type CharT
difference_type Traits::off_type
pointer /* unspecified, usually CharT* */
reference CharT
char_type CharT
traits_type Traits
int_type typename traits::int_type
streambuf_type std::basic_streambuf<CharT, Traits>
istream_type std::basic_istream<CharT, Traits>
/* proxy */ Implementation-defined class type. The name proxy is for exposition only.
A proxy object holds a char_type character and a streambuf_type* pointer.
Deferencing a proxy object with operator* yields the stored character.

Member types iterator_category, value_type, difference_type, pointer and reference are required to be obtained by inheriting from std::iterator<std::input_iterator_tag, CharT, Traits::off_type, /* unspecified, usually CharT* */, CharT>.

 (until C++17)

Member functions

constructs a new istreambuf_iterator
(public member function)
(destructor)
(implicitly declared)
 destructs an istreambuf_iterator
(public member function)
(since C++11)(until C++17)
 obtains a copy of the current character
accesses a member of the current character, if CharT has members
(public member function)
advances the iterator
(public member function)
tests if both istreambuf_iterators are end-of-stream or if both are valid
(public member function)

Non-member functions

(removed in C++20)
 compares two istreambuf_iterators
(function template)

Example

#include <string>
#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::istreambuf_iterator<char> it{in}, end;
    std::string ss{it, end};
    std::cout << "ss has " << ss.size() << " bytes; "
                 "it holds \"" << ss << "\"\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;
    std::cout << "after incrementing i2, but not i1:\n"
                 "i1 returns '" << *i1 << "'\n"
                 "i2 returns '" << *i2 << "'\n";
}

Output:

ss has 12 bytes; it holds "Hello, world"
i1 returns 'a'
i2 returns 'a'
after incrementing i1, but not i2:
i1 returns 'b'
i2 returns 'b'
after incrementing i2, but not i1:
i1 returns 'c'
i2 returns 'c'

See also

output iterator that writes to std::basic_streambuf
(class template)
input iterator that reads from std::basic_istream
(class template)

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