NAME¶

std::ranges::views::istream,std::ranges::basic_istream_view,std::ranges::istream_view, - std::ranges::views::istream,std::ranges::basic_istream_view,std::ranges::istream_view,

Synopsis¶

Defined in header <ranges>
template< std::movable Val, class CharT, class Traits =
std::char_traits<CharT> >

requires std::default_initializable<Val> &&
/*stream-extractable*/<Val,CharT,Traits> (1) (since C++20)
class basic_istream_view

: public
ranges::view_interface<basic_istream_view<Val,CharT,Traits>>
Helper templates
template< class Val > (2) (since C++20)
using istream_view = ranges::basic_istream_view<Val, char>;
template< class Val > (3) (since C++20)
using wistream_view = ranges::basic_istream_view<Val, wchar_t>;
Customization point objects
namespace views {

template< class T > (4) (since C++20)
inline constexpr /*unspecified*/ istream = /*unspecified*/;

}
Helper concepts
template< class Val, class CharT, class Traits >

concept /*stream-extractable*/ = (exposition
requires(std::basic_istream<CharT,Traits>& is, Val& t) { (5) only*)
is >> t;

};

1) A range factory that generates a sequence of elements by repeatedly calling
operator>>.
2,3) Convenience alias templates for character types char and wchar_t.
4) views::istream<T>(e) is expression-equivalent to (has the same effect as)
ranges::basic_istream_view<T, typename U::char_type, typename U::traits_type>(e) for
any suitable subexpressions e, where U is std::remove_reference_t<decltype(e)>. The
program is ill-formed if U is not both publicly and unambiguously derived from
std::basic_istream<typename U::char_type, typename U::traits_type>, which may result
in a substitution failure.
5) The exposition-only concept /*stream-extractable*/<Val,CharT,Traits> is satisfied
when lvalue of Val can be extracted from lvalue of std::basic_istream<CharT,Traits>.

The iterator type of basic_istream_view is move-only: it does not meet the
LegacyIterator requirements, and thus does not work with pre-C++20 algorithms.

Member functions¶

constructor constructs a basic_istream_view
(public member function)
begin returns an iterator
(public member function)
end returns std::default_sentinel
(public member function)
Inherited from std::ranges::view_interface
although basic_istream_view is derived from
(none) std::ranges::view_interface, it cannot use any of inherited member
functions.

std::ranges::basic_istream_view::basic_istream_view

constexpr explicit (since C++20)
basic_istream_view( std::basic_istream<CharT, Traits>& stream );

Initializes the stored pointer to stream with std::addressof(stream), and
value-initializes the stored value of Val.

std::ranges::basic_istream_view::begin

constexpr auto begin(); (since C++20)

Equivalent to *stream_ >> value_; return /*iterator*/{*this};, where stream_ is the
stored pointer to stream and value_ is the stored value of Val.

std::ranges::basic_istream_view::end

constexpr std::default_sentinel_t end() const noexcept; (since C++20)

Equivalent to return std::default_sentinel;.

Nested classes

iterator the iterator type of basic_istream_view
(C++20) (exposition-only member class*)

Example¶

// Run this code

#include <algorithm>
#include <iomanip>
#include <iostream>
#include <iterator>
#include <ranges>
#include <sstream>
#include <string>

int main()
{
auto words = std::istringstream{"today is yesterday’s tomorrow"};
for (const auto& s : std::views::istream<std::string>(words))
std::cout << std::quoted(s, '/') << ' ';
std::cout << '\n';

auto floats = std::istringstream{"1.1 2.2\t3.3\v4.4\f55\n66\r7.7 8.8"};
std::ranges::copy(
std::views::istream<float>(floats),
std::ostream_iterator<float>{std::cout, ", "}
);
std::cout << '\n';
}

Output:¶

/today/ /is/ /yesterday’s/ /tomorrow/
1.1, 2.2, 3.3, 4.4, 55, 66, 7.7, 8.8,

Defect reports

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

DR Applied to Behavior as published Correct behavior
default constructor was provided as removed along with the
P2325R3 C++20 view requirement
must be default_initializable
LWG 3568 C++20 P2325R3 accidentally made the stored restored to
value default-initialized value-initialization
ranges::istream_view was a function made an alias template;
P2432R1 C++20 template and customization point objects
did not follow the naming convention added

See also¶

istream_iterator input iterator that reads from std::basic_istream
(class template)