std::gcd | C++ inbuilt function for finding GCD

In many competitive programming problems, we need to find greatest common divisor also known as gcd. Euclids algorithm to find gcd has been discussed here.
C++ has the built-in function for calculating GCD. This function is present in header file. 
Syntax for C++14 :

 Library: 'algorithm'
 __gcd(m, n) 
Parameter :  m, n
Return Value :  0 if both m and n are zero, 
else gcd of m and n.

Syntax for C++17 :

Library: 'numeric'
gcd(m, n)
Parameter :  m, n
Return Value :  0 if both m and n are zero,
else gcd of m and n.

// CPP program to illustrate
// gcd function of C++ STL
#include <iostream>
#include <algorithm> 
// #include<numeric> for C++17

using namespace std;

int main()
{
    cout << "gcd(6, 20) = " << __gcd(6, 20) << endl; // gcd(6,20) for C++17
}

gcd(6, 20) = 2

Time Complexity: O(logn)
Auxiliary Space: O(1)

Program to Find the gcd of all numbers in a vector.

#include<bits/stdc++.h>
#include <iostream>
#include <algorithm>
using namespace std;
int main()
{
    vector<int> numbers = { 12, 15, 18, 21, 24 };
    int ans =__gcd(numbers[0], numbers[1]);
    for (int i = 2; i < numbers.size(); i++)
    {
        ans = __gcd(ans, numbers[i]);
    }
    cout << "The GCD of the numbers in the vector is: " <<ans<<endl;
    return 0;
}

The GCD of the numbers in the vector is: 3

Time Complexity: O(k*logn)
Auxiliary Space: O(k)

Note: If either M or N is not an integer type, or if either is (possibly cv-qualified) bool, the program is ill-formed. Also, If either |m| or |n| is not representable as a value of type std::common_type_t, the behavior is undefined. 
 

// CPP program to illustrate
// undefined behavior of
// gcd function of C++ STL
#include <iostream>
#include <algorithm> 
// #include<numeric> for C++17

using namespace std;

int main()
{
    cout << "gcd(2.0, 8) = " << __gcd(2.0, 8) << endl; // gcd(2.0,8) for C++17
}

Output: 
Error, As the data type float is not supported by std::gcd.