std::ranges::basic_istream_view, std::ranges::istream_view

 

C++

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Standard Library Headers

Freestanding and hosted implementations

Named requirements

Language support library

Concepts library (C++20)

Diagnostics library

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)

Atomic operations library (C++11)

Thread support library (C++11)

Technical Specifications

 

Ranges library

Range access
begin cbegin end cend	rbegin crbegin rend crend	size ssize data cdata	empty
Range primitives
iterator_tsentinel_t	range_size_trange_difference_t	range_value_t	range_reference_trange_rvalue_reference_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
Semiregular wrapper
semiregular_box
Factories
empty_viewviews::empty	single_viewviews::single	iota_viewviews::iota	basic_istream_viewistream_view
Adaptors
views::all_tviews::all common_viewviews::common join_viewviews::join split_viewviews::split	take_viewviews::take drop_viewviews::drop take_while_viewviews::take_while drop_while_viewviews::drop_while	transform_viewviews::transform reverse_viewviews::reverse filter_viewviews::filter ref_view	views::counted elements_viewviews::elements keys_viewviews::keys values_viewviews::values

 

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)
template< class Val, class CharT, class Traits > basic_istream_view<Val,CharT,Traits> istream_view( std::basic_istream<CharT,Traits>& s );	(2)	(since C++20)

1) A range factory that generates a sequence of elements by repeatedly calling operator>>.

2) Returns a basic_istream_view, deducing CharT and Traits from s. Equivalent to return basic_istream_view<Val, CharT, Traits>{s}.

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>. Its definition is equivalent to

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

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. Furthermore, because its std::iterator_traits does not provide a iterator_category, it does not work with standard iterator adaptors.

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)

std::ranges::basic_istream_view::basic_istream_view

basic_istream_view() = default;	(1)
constexpr explicit basic_istream_view( std::basic_istream<CharT, Traits>& stream );	(2)

1) Default constructor. Value-initializes the stored pointer to the stream and the stored value of Val. Use of an iterator to default constructed istream view is undefined behavior.

2) 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();

Equivalent to:

if (stream_) {
    *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;

Equivalent to return std::default_sentinel;.

Nested classes

std::ranges::basic_istream_view::iterator

struct /*iterator*/;

The return type of basic_istream_view::begin.

This is an input_iterator.

Member types
Member type	Definition
iterator_concept	std::input_iterator_tag
difference_type	std::ptrdiff_t
value_type	Val
Member functions
(constructor)	constructs an iterator (public member function)
operator=	the copy assignment operator is deleted (public member function)
operator++	advances or decrements the iterator (public member function)
operator*	returns the current element (public member function)
Non-member functions
operator==	compares with a std::default_sentinel_t (public member function)

std::ranges::basic_istream_view::iterator::iterator

/*iterator*/() = default;	(1)
constexpr explicit /*iterator*/( basic_istream_view& parent );	(2)
/*iterator*/( const /*iterator*/& ) = delete;	(3)
/*iterator*/( /*iterator*/&& ) = default;	(4)

1) Default constructor. Constructs an end iterator that compares equal to std::default_sentinel.

2) Constructs an iterator from the parent basic_istream_view.

3) The copy constructor is deleted. The iterator is not copyable.

4) The move constructor is defaulted. The iterator is movable.

std::ranges::basic_istream_view::iterator::operator=

/*iterator*/& operator=( const /*iterator*/& ) = delete;	(1)
/*iterator*/& operator=( /*iterator*/&& ) = default;	(2)

3) The copy assignment operator is deleted. The iterator is not copyable.

4) The move assignment operator is defaulted. The iterator is movable.

std::ranges::basic_istream_view::iterator::operator++

/*iterator*/& operator++();	(1)
void operator++(int);	(2)

Reads a value from the underlying stream and stores it into the parent basic_istream_view.

Return value

1) *this

2) (none)

std::ranges::basic_istream_view::iterator::operator*

Val& operator*() const;

Returns a reference to the stored value.

operator==(std::ranges::basic_istream_view::iterator, std::default_sentinel)

friend bool operator==( const /*iterator*/& x, std::default_sentinel_t );

Compares an iterator with std::default_sentinel_t.

Returns true if *this does not have a parent basic_istream_view, or if an error has occurred on the underlying stream.

This function is not visible to ordinary unqualified or qualified lookup, and can only be found by argument-dependent lookup when std::ranges::basic_istream_view::iterator is an associated class of the arguments.

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,

See also

istream_iterator

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