std::ranges::views::istream, std::ranges::basic_istream_view, std::ranges::istream_view, std::ranges::wistream_view
| Defined in header <ranges>
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| template< std::movable Val, class CharT, class Traits = std::char_traits<CharT> > |
(1) | (since C++20) |
| Helper templates |
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| 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 |
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| namespace views { template< class T > |
(4) | (since C++20) |
| Helper concepts |
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template< class Val, class CharT, class Traits > concept /*stream-extractable*/ = |
(5) | (exposition only*) |
U is std::remove_reference_t<decltype(e)>.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.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. 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.
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 std::ranges::view_interface | |||
| (C++23) |
returns a constant iterator to the beginning of the range. (public member function of std::ranges::view_interface<D>) | ||
| (C++23) |
returns a sentinel for the constant iterator of the range. (public member function of std::ranges::view_interface<D>) | ||
|
Although |
(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 asview must be default_initializable
|
removed along with the requirement |
| P2432R1 | C++20 | ranges::istream_view was a function templateand did not follow the naming convention |
made an alias template; customization point objects added |
See also
| input iterator that reads from std::basic_istream (class template) |