std::dynamic_extent
From cppreference.com
Defined in header <span> | ||
inlineconstexprstd::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 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.
| (since C++23) |
| (since C++26) |
[edit]Note
Since std::size_t is an unsigned type, an equivalent definition is:
inlineconstexprstd::size_t dynamic_extent =-1;
See integral conversions.
[edit]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_viewconst name, std::size_t ex){std::cout<< name <<", ";if(std::dynamic_extent== ex)std::cout<<"dynamic extent\n";elsestd::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
[edit]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) |
