std::dynamic_extent
From cppreference.com
| Defined in header <span>
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inline constexpr std::size_t dynamic_extent = std::numeric_limits<std::size_t>::max();
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(since C++20) | |
std::dynamic_extent is a constant of type std::size_t that is generally used to indicate that any type using std::dynamic_extent will dynamically store its value (e.g., size) rather than having the value statically known in the type.
It is being used in several contexts:
- To differentiate std::span of static and dynamic extent.
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(since C++23) |
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(since C++26) |
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 (std::dynamic_extent == ex)
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
(C++20) |
a non-owning view over a contiguous sequence of objects (class template) |
(C++23) |
a descriptor of a multidimensional index space of some rank (class template) |
