NAME

std::dynamic_extent - std::dynamic_extent

Synopsis

Defined in header <span>
inline constexpr std::size_t dynamic_extent = (since C++20)
std::numeric_limits<std::size_t>::max();

std::dynamic_extent is a constant of type std::size_t that is used to differentiate
std::span of static and dynamic extent.

Note

Since std::size_t is an unsigned type, an equivalent definition is:

inline constexpr std::size_t dynamic_extent = -1;

See integral conversions.

Example

// Run this code

#include <array>
#include <cassert>
#include <cstddef>
#include <iostream>
#include <span>
#include <string_view>
#include <vector>

int main()
{
auto print = [](std::string_view const name, std::size_t ex) {
std::cout << name << ", ";
if (ex == std::dynamic_extent) {
std::cout << "dynamic extent\n";
} else {
std::cout << "static extent = " << ex << '\n';
}
};

int a[]{1,2,3,4,5};

std::span span1{a};
print("span1", span1.extent);

std::span<int, std::dynamic_extent> span2{a};
print("span2", span2.extent);

std::array ar{1,2,3,4,5};
std::span span3{ar};
print("span3", span3.extent);

std::vector v{1,2,3,4,5};
std::span span4{v};
print("span4", span4.extent);
}

Output:

span1, static extent = 5
span2, dynamic extent
span3, static extent = 5
span4, dynamic extent

See also

span a non-owning view over a contiguous sequence of objects
(C++20) (class template)