basic_istream_view class (C++ Standard Library)
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