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

 

C++

Compiler support

Freestanding and hosted

Language

Standard library headers

Named requirements

Feature test macros (C++20)

Language support library

Concepts library (C++20)

Metaprogramming library (C++11)

Diagnostics library

General utilities library

Strings library

Containers library

Iterators library

Ranges library (C++20)

Algorithms library

Numerics library

Localizations library

Input/output library

Filesystem library (C++17)

Regular expressions library (C++11)

Concurrency support library (C++11)

Technical specifications

Symbols index

External libraries

 

Ranges library

Range access
begin cbegin end cend	rbegin crbegin rend crend	size ssize data cdata	empty
Range conversions
to (C++23)
Range primitives
iterator_tsentinel_t	range_size_trange_difference_t	range_reference_trange_rvalue_reference_t	range_value_t
Dangling iterator handling
dangling	borrowed_iterator_t	borrowed_subrange_t
Range concepts
range borrowed_range    sized_range	common_range view viewable_range	input_range output_range forward_range	bidirectional_range random_access_range contiguous_range
Views
view_interface	subrange
Factories
empty_viewviews::empty	single_viewviews::single	iota_viewviews::iota	basic_istream_viewviews::istream
Adaptors
views::all_tviews::all ref_view owning_view common_viewviews::common reverse_viewviews::reverse views::counted zip_viewviews::zip (C++23)(C++23) zip_transform_viewviews::zip_transform (C++23)(C++23)	take_viewviews::take take_while_viewviews::take_while drop_viewviews::drop drop_while_viewviews::drop_while adjacent_viewviews::adjacent (C++23)(C++23) adjacent_transform_viewviews::adjacent_transform (C++23)(C++23)	elements_viewviews::elements keys_viewviews::keys values_viewviews::values transform_viewviews::transform join_with_viewviews::join_with (C++23)(C++23) slide_viewviews::slide (C++23)(C++23)	filter_viewviews::filter join_viewviews::join split_viewviews::split lazy_split_viewviews::lazy_split chunk_viewviews::chunk (C++23)(C++23) chunk_by_viewviews::chunk_by (C++23)(C++23)
Range adaptor objects
Range adaptor closure objects
Helper items
copyable-box	simple-view

 

std::ranges::basic_istream_view

Member functions

basic_istream_view::basic_istream_view (C++20)

basic_istream_view::begin (C++20)

basic_istream_view::end (C++20)

Iterator

basic_istream_view::iterator::iterator (C++20)

basic_istream_view::iterator::operator= (C++20)

basic_istream_view::iterator::operator++ (C++20)

basic_istream_view::iterator::operator* (C++20)

operator==(basic_istream_view::iterator) (C++20)

 

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 >     inline 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)	(since C++20)

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.

Expression-equivalent

Expression e is expression-equivalent to expression f, if

• e and f have the same effects, and
• either both are constant subexpressions or else neither is a constant subexpression, and
• either both are potentially-throwing or else neither is potentially-throwing (i.e. noexcept(e) == noexcept(f)).

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. For exposition purposes, the cv-unqualified version of its type is denoted as __istream_fn<T>.

All instances of __istream_fn<T> are equal. The effects of invoking different instances of type __istream_fn<T> on the same arguments are equivalent, regardless of whether the expression denoting the instance is an lvalue or rvalue, and is const-qualified or not (however, a volatile-qualified instance is not required to be invocable). Thus, views::istream<T> can be copied freely and its copies can be used interchangeably.

Given a set of types Args..., if std::declval<Args>()... meet the requirements for arguments to views::istream<T> above, __istream_fn<T> models

• std::invocable<__istream_fn<T>, Args...>,
• std::invocable<const __istream_fn<T>, Args...>,
• std::invocable<__istream_fn<T>&, Args...>, and
• std::invocable<const __istream_fn<T>&, Args...>.
  

Otherwise, no function call operator of __istream_fn<T> participates in overload resolution.

Member functions

(constructor) (C++20)	constructs a basic_istream_view (public member function)
begin (C++20)	returns an iterator (public member function)
end (C++20)	returns std::default_sentinel (public member function)
Inherited from std::ranges::view_interface
(none)	Although basic_istream_view is derived from std::ranges::view_interface, it cannot use any of inherited member functions.

std::ranges::basic_istream_view::basic_istream_view

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

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 (C++20)

the iterator type of basic_istream_view, the name is exposition-only (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::ranges::istream_view<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::ranges::istream_view<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
P2325R3	C++20	default constructor was provided as view must be default_initializable	removed along with the requirement
LWG 3568	C++20	P2325R3 accidentally made the stored value default-initialized	restored to value-initialization
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

istream_iterator

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