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std::ranges::views::istream, std::ranges::basic_istream_view, std::ranges::istream_view, std::ranges::wistream_view - cppreference.com

From cppreference.com

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> class basic_istream_view : public ranges::view_interface<basic_istream_view<Val, CharT, Traits>>

 (1) (since C++20)

Helper templates

template< class Val > using istream_view = ranges::basic_istream_view<Val, char>;

 (2) (since C++20)

template< class Val > using wistream_view = ranges::basic_istream_view<Val, wchar_t>;

 (3) (since C++20)

Customization point objects

namespace views { template< class T > constexpr /* unspecified */ istream = /* unspecified */; }

 (4) (since C++20)

Helper concepts

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

 (5) (exposition only*)

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 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 type Val can be extracted from lvalue of type 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.

Customization point objects

The name views::istream<T> denotes a customization point object, which is a const function object of a literal semiregular class type. See CustomizationPointObject for details.

Data members

Member Definition
std::basic_istream<CharT, Traits>* stream_ a pointer to the input stream
(exposition-only member object*)
Val value_ the stored value
(exposition-only member object*)

Member functions

constructs a basic_istream_view
(public member function)
returns an iterator
(public member function)
returns std::default_sentinel
(public member function)
Inherited from ranges::view_interface

(C++23)

 returns a constant iterator to the beginning of the range
(public member function of std::ranges::view_interface<D>) [edit]

(C++23)

 returns a sentinel for the constant iterator of the range
(public member function of std::ranges::view_interface<D>) [edit]

Although basic_istream_view is derived from ranges::view_interface, it cannot use any of inherited member functions.

(until C++23)

std::ranges::basic_istream_view::basic_istream_view

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

 (since C++20)

Initializes stream_ with std::addressof(stream), and value-initializes value_ .

std::ranges::basic_istream_view::begin

constexpr auto begin();

 (since C++20)

Equivalent to *stream_ >> value_ ; return iterator {*this};.

std::ranges::basic_istream_view::end

constexpr std::default_sentinel_t end() const noexcept;

 (since C++20)

Returns std::default_sentinel.

Nested classes

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

Example

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

See also