NAME¶

std::istreambuf_iterator - std::istreambuf_iterator

Synopsis¶

Defined in header <iterator>
template< class CharT, class Traits = std::char_traits<CharT> >

class istreambuf_iterator
: public std::iterator<std::input_iterator_tag, (until C++17)
CharT, typename Traits::off_type,

/* unspecified */, CharT>
template< class CharT, class Traits = std::char_traits<CharT> > (since C++17)
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 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 (since C++11)
default constructor, and a trivial destructor.

Member types¶

Member type Definition
iterator_category std::input_iterator_tag
value_type CharT
difference_type typename Traits::off_type
pointer /* unspecified */
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>
Implementation-defined class type. The name proxy is for
exposition only.
/* proxy */ A proxy object holds a char_type character and a streambuf_type*
pointer.
Dereferencing 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 (until C++17)
std::iterator<std::input_iterator_tag, CharT, typename
Traits::off_type, /* unspecified */, CharT>.

The member type pointer is usually CharT* (see below).

Member functions¶

constructor constructs a new istreambuf_iterator
(public member function)
destructor destructs an istreambuf_iterator
(implicitly declared) (public member function)
operator* obtains a copy of the current character
(public member function)
operator++ advances the iterator
operator++(int) (public member function)
tests if both istreambuf_iterators are end-of-stream or if
equal both are valid
(public member function)

Non-member functions¶

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

Notes¶

The resolution of LWG issue 659 introduced operator->. It is expected that given an
std::istreambuf_iterator i, the expressions (*i).m and i->m have the same effect.

However, the resolution does not provide a formal specification of its behavior.
Thus it is implemented differently, including returning nullptr, returning the
address of a temporary, or does even provide the member at all. Its intended
behavior can hardly be achieved, and it is removed by the resolution of LWG issue
2790.

The resolution of LWG issue 659 also made the member type pointer unspecified in
order to allow operator-> to return a proxy. This is to allow operator-> to compile
when CharT is not a class type.

Example¶

// Run this code

#include <iostream>
#include <iterator>
#include <sstream>
#include <string>

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'

Defect reports

The following behavior-changing defect reports were applied retroactively to
previously published C++ standards.

DR Applied to Behavior as published Correct behavior
1. std::istreambuf_iterator did not have
LWG 659 C++98 operator-> 1. added
2. the member type pointer was specified as 2. made unspecified
CharT*
LWG 2790 C++98 the operator-> added by LWG issue 659 was removed
not useful

See also¶

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