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

Standard library headers

Named requirements

Feature test macros(C++20)

Language support library

Concepts library(C++20)

Diagnostics library

Memory management library

Metaprogramming library(C++11)

General utilities library

Containers library

Iterators library

Ranges library(C++20)

Algorithms library

Strings library

Text processing library

Numerics library

Date and time library

Input/output library

Filesystem library(C++17)

Concurrency support library(C++11)

Execution control library(C++26)

Technical specifications

Symbols index

External libraries

 

Ranges library

Range access begin cbegin   end cend rbegin crbegin   rend crend size ssize   data cdata reserve_hint (C++26)   empty

Range conversions std::from_range_t std::from_range (C++23)(C++23)     to (C++23)

Dangling iterator handling dangling borrowed_iterator_t borrowed_subrange_t

Range primitives
range_size_trange_difference_trange_value_t elements_of (C++23)	iterator_tconst_iterator_tsentinel_tconst_sentinel_t (C++23)(C++23)	range_reference_trange_const_reference_trange_rvalue_reference_trange_common_reference_t (C++23)

Range concepts
range borrowed_range    common_range	sized_range viewable_range    view	input_range output_range forward_range	bidirectional_range    random_access_range contiguous_range	approximately_sized_range (C++26) constant_range (C++23)

Views
view_interface	subrange

Range factories
empty_viewviews::empty	single_viewviews::single	basic_istream_viewviews::istream	iota_viewviews::iota	repeat_viewviews::repeat (C++23)(C++23)

Range adaptors
views::all_tviews::all as_rvalue_viewviews::as_rvalue (C++23)(C++23)   filter_viewviews::filter transform_viewviews::transform take_viewviews::take take_while_viewviews::take_while common_viewviews::common views::counted to_input_viewviews::to_input (C++26)(C++26)	ref_view drop_viewviews::drop drop_while_viewviews::drop_while lazy_split_viewviews::lazy_split split_viewviews::split join_viewviews::join join_with_viewviews::join_with (C++23)(C++23)   concat_viewviews::concat (C++26)(C++26) cache_latest_viewviews::cache_latest (C++26)(C++26)	owning_view reverse_viewviews::reverse as_const_viewviews::as_const (C++23)(C++23) elements_viewviews::elements keys_viewviews::keys values_viewviews::values enumerate_viewviews::enumerate (C++23)(C++23) zip_viewviews::zip (C++23)(C++23) zip_transform_viewviews::zip_transform (C++23)(C++23)	adjacent_viewviews::adjacent (C++23)(C++23) views::pairwise (C++23) adjacent_transform_viewviews::adjacent_transform (C++23)(C++23) views::pairwise_transform (C++23) chunk_viewviews::chunk (C++23)(C++23) slide_viewviews::slide (C++23)(C++23) chunk_by_viewviews::chunk_by (C++23)(C++23) stride_viewviews::stride (C++23)(C++23) cartesian_product_viewviews::cartesian_product (C++23)(C++23)

Range generators std::generator (C++23)

Range adaptor closure objects range_adaptor_closure (C++23)

Range adaptor objects

Helper items
copyable-box movable-box (until C++23)  (C++23)	simple-view non-propagating-cache

 

std::ranges::basic_istream_view

Member functions

basic_istream_view::basic_istream_view

basic_istream_view::begin

basic_istream_view::end

Iterator

basic_istream_view::iterator::iterator

basic_istream_view::iterator::operator=

basic_istream_view::iterator::operator++

basic_istream_view::iterator::operator*

operator==(basic_istream_view::iterator)

 

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     :publicranges::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 literalsemiregular 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*)
Valvalue_	the stored value (exposition-only member object*)

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
cbegin (C++23)	returns a constant iterator to the beginning of the range (public member function of std::ranges::view_interface<D>)
cend (C++23)	returns a sentinel for the constant iterator of the range (public member function of std::ranges::view_interface<D>)

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

(until C++23)

std::ranges::basic_istream_view::basic_istream_view

constexprexplicit     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

constexprauto begin();		(since C++20)

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

std::ranges::basic_istream_view::end

constexprstd::default_sentinel_t end()constnoexcept;		(since C++20)

Returns std::default_sentinel.

Nested classes

iterator

the iterator type of basic_istream_view (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(constauto& 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

istream_iterator

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