std::extent() template in C++ with Examples

The std::is_const template of C++ STL is present in the <type_traits> header file. If A is an array that has a rank greater than B, the extent is the bound of the Ath dimension and if B is zero and A is the array of unknown bound, than the extent value is zero.

Header File:

#include<type_traits>

Syntax:

template 
  <class A, unsigned B = 0>
  struct extent;

Parameters: It accepts the following parameters:

• A : It represents a particular type.
• B : It represents the dimensions for which the extent is to be obtained.

Below are the programs to demonstrate std::extent():

Program 1:

// C++ program to demonstrate
// std::extent()

#include <bits/stdc++.h>
#include <type_traits>
using namespace std;

// Driver Code
int main()
{
    // By default dimension is zero
    cout << extent<int[3]>::value << endl;
    cout << extent<int[3][4], 0>::value << endl;
    cout << extent<int[3][4], 1>::value << endl;
    cout << extent<int[3][4], 2>::value << endl;
    cout << extent<int[]>::value << endl;

    const int ints[] = { 1, 2, 3, 4 };

    // Used to print the size of array
    cout << extent<decltype(ints)>::value
         << endl;

    return 0;
}

Output:

3
3
4
0
0
4

Program 2:

// C++ program to demonstrate
// std::extent()

#include <bits/stdc++.h>
#include <type_traits>
using namespace std;

// Driver Code
int main()
{
    typedef int gfg[][50][70];
    cout << "gfg array (int[][50][70]):" << endl;
    cout << "rank: " << rank<gfg>::value << endl;
    cout << extent<gfg, 0>::value << endl;
    cout << extent<gfg, 1>::value << endl;
    cout << extent<gfg, 2>::value << endl;
    cout << extent<gfg, 3>::value << endl;
    return 0;
}

Output:

gfg array (int[][50][70]):
rank: 3
0
50
70
0

Reference: http://www.cplusplus.com/reference/type_traits/extent/