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

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


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

inline constexpr std::size_t dynamic_extent = -1;

See integral conversions.


#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);


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

See also

a non-owning view over a contiguous sequence of objects
(class template)

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