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basic_istream_view class (C++ Standard Library)

  • Artikkeli

A view of successive elements from an input stream.

Syntax

template<movable Val, class CharT, class Traits>
    requires default_initializable<Val> &&
    stream_extractable <Val, CharT, Traits>
class basic_istream_view : public view_interface<basic_istream_view<Val, CharT, Traits>>;

Template parameters

CharT
The character type of the stream.

Traits
Optional. Provides details about the character type of the stream regarding comparing characters, determining the length of a string made up of that character type, and so on. An example trait is char_traits<wchar_t>. If not specified, defaults to char_traits<CharT>.

Val
The type of the elements to extract. For example, double given a stream of: "1.1 2.2 3.3"

stream_extractable refers to the requirement (concept) that the type Val can be extracted from a stream using the operator>> function. It's equivalent to:

template<class Val, class CharT, class Traits>
concept stream_extractable =
  requires(std::basic_istream<CharT,Traits>& is, Val& t) {
    is >> t;
  };

View characteristics

For a description of the following entries, see View class characteristics

Characteristic Description
Range adaptor istream
Underlying range None
Element type The same as Val
View iterator category input_range
Sized No
Is const-iterable No
Common range No
Borrowed range No

Specializations:istream_view and wistream_view

Convenience alias templates are provided for char and wchar_t streams, as follows:

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

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

1) Reads elements from an input stream composed of char characters.
2) Reads elements from an input stream composed of wchar_t characters.

For 1) and 2), Val refers to the type of the elements to extract. For example, Val is double given a stream of: "1.1 2.2 3.3"

Members

Member functions Description
ConstructorsC++20 Construct a basic_istream_view.
beginC++20 Read the first value and get an iterator for the view.
endC++20 Returns std::default_sentinel

No member functions are inherited from view_interface.

Requirements

Header: <ranges> (since C++20)

Namespace: std::ranges

Compiler Option: /std:c++20 or later is required.

Constructors

Construct an instance of a basic_istream_view.

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

Parameters

stream
The stream to read from.

For information about the template parameter type, see Template parameters.

Return value

A basic_istream_view instance. The basic_istream_view internal stream pointer is initialized to addressof(stream).

Remarks

The best way to create a basic_istream_view is by using the views::istream range adaptor. Range adaptors are the intended way to create view classes. The view types are exposed in case you want to create your own custom view type.

Example: basic_istream_view, istream_view, and wistream_view

// requires /std:c++20, or later
#include <ranges>
#include <iostream>
#include <sstream>

int main()
{
    // range adaptor
    std::istringstream streamOfdoubles{ "1.1 2.2 3.3 4.4 5.5" };
    for (const auto& elem : std::views::istream<double>(streamOfdoubles))
    {
        std::cout << elem << ' '; // 1.1 2.2 3.3 4.4 5.5
    }
    std::cout << '\n';

    // range adaptor - create a wistream_view
    std::wistringstream streamOfInts{ L"1 2 3 4 5" };
    for (const auto& elem : std::views::istream<int>(streamOfInts))
    {
        std::cout << elem << ' '; // 1 2 3 4 5
    }
    std::cout << '\n';

    // istream_view alias
    std::istringstream cpu1{ "8 0 8 0" };
    // equivalent std::ranges::istream_view<int, char>
    for (const auto& elem : std::ranges::istream_view<int>{cpu1})
    {
        std::cout << elem; // 8080
    }
    std::cout << '\n';

    // wistream_view alias
    std::wistringstream cpu2{ L"6 5 0 2" };
    // equivalent std::ranges::istream_view<int, wchar_t>
    for (const auto& elem : std::ranges::wistream_view<int>{cpu2})
    {
        std::cout << elem; // 6502
    }
    std::cout << '\n';

    // specify all template arguments
    std::wistringstream misc(L"S T L");
    std::ranges::basic_istream_view<wchar_t, wchar_t, std::char_traits<wchar_t>> basic{misc};
    for (const auto& elem : basic)
    {
        std::wcout << elem << ' '; // S T L
    }
}

1.1 2.2 3.3 4.4 5.5
1 2 3 4 5
8080
6502
S T L

begin

Read the first value and get an iterator to the view.

constexpr auto begin();

Parameters

None.

Return value

An iterator pointing at the first element in the basic_istream_view.

end

Get the sentinel at the end of the view.

constexpr std::default_sentinel_t end() const noexcept;

Parameters

None.

Return value

default_sentinel_t

See also

<ranges>
View classes