std::span::first(3) | C++ Standard Libary | std::span::first(3) |
NAME¶
std::span::first - std::span::first
Synopsis¶
template< std::size_t Count >
constexpr std::span<element_type, Count> first() const;
constexpr std::span<element_type, std::dynamic_extent> first( size_type
Count )
const;
Obtains a span that is a view over the first Count elements of this span. The
program is ill-formed if Count > Extent. The behavior is undefined if
Count >
size().
Return value¶
A span r that is a view over the first Count elements of *this,
such that r.data()
== this->data() && r.size() == Count.
Example¶
// Run this code
#include <iostream>
#include <span>
#include <string_view>
void print(std::string_view const title,
/* std::ranges::forward_range */ auto const& container) {
std::cout << title << "[" << std::size(container)
<< "]{ ";
for (auto const& elem : container)
std::cout << elem << ", ";
std::cout << "};\n";
}
void run_game(std::span<const int> span)
{
print("span: ", span);
std::span<const int, 5> span_first = span.first<5>();
print("span.first<5>(): ", span_first);
std::span<const int, std::dynamic_extent> span_first_dynamic =
span.first(4);
print("span.first(4): ", span_first_dynamic);
}
int main()
{
int a[8]{ 1, 2, 3, 4, 5, 6, 7, 8, };
print("int a", a);
run_game(a);
}
Output:¶
int a[8]{ 1, 2, 3, 4, 5, 6, 7, 8, };
span: [8]{ 1, 2, 3, 4, 5, 6, 7, 8, };
span.first<5>(): [5]{ 1, 2, 3, 4, 5, };
span.first(4): [4]{ 1, 2, 3, 4, };
See also¶
last obtains a subspan consisting of the last N elements of the
sequence
(public member function)
subspan obtains a subspan
(public member function)
2022.07.31 | http://cppreference.com |