Why __gcd() is throwing error in macOS mojave?

Question

#include <iostream>
#include <vector>
#include <algorithm>
#include <numeric>
 
using namespace std;

int main() {
    int n;
    cin >> n;
    vector<int> a(n);
   
    for(int i = 0; i < n; ++i)
        cin >> a[i];

    int ans = a[0];
    for(int i = 1; i < n; ++i)
       ans = __gcd(ans, a[i]);

    cout << ans << endl;

    return 0;
}

It is throwing the following error:

error: static_assert failed due to requirement '!is_signed::value'

note: in instantiation of function template specialization 'std::__1::__gcd' requested here ans = __gcd(ans, a[i]);

I am using command g++ -std=c++17 which worked for every program except this one.

This code is working without error on code.hackerearth.com online compiler which uses g++ 5.4.0

EDIT: Removed bits/stdc++.h header and included required headers only.

After removing also the same problem is happening.

The SAME code is running properly in online ide. Link of one such ide is ONLINE IDE

Using their c++ compiler and function __gcd(a, b) doesn't give any error but, when I change it to gcd(a, b) in the same ide, it does give error that this function definition is not found.

When I run the same code in my local machine, everything happens in just the opposite way. __gcd(a, b) doesn't work while gcd(a, b) works.

__gcd is private, don't use it... What is not clear in the error message? It only works with unsigned types. — Marc Glisse, Oct 20 '18 at 13:30
Please read [Why should I not #include ?](https://stackoverflow.com/questions/31816095/why-should-i-not-include-bits-stdc-h) — Some programmer dude, Oct 20 '18 at 13:32
@vivek: that is unfortunate. Still no excuse to use a implementation-private function — MSalters, Oct 21 '18 at 09:40
@vivek: the implementation-private part refers to __gcd. Double underscores signify nonstandard functions for implementation-internal use. The header was another problem — MSalters, Oct 24 '18 at 13:34

Matthieu Brucher · Answer 1 · 2018-10-20T13:36:03.163

2

Don't use bit/C++.h, it's a private header.

Use proper C++ functions: https://en.cppreference.com/w/cpp/numeric/gcd

They support signed integers.

#include <iostream>
#include <vector>
#include <numeric>

using namespace std;

int main() {
int n;
cin >> n;
vector<int> a(n);

for(int i = 0; i < n; ++i)
    cin >> a[i];

int ans = a[0];
for(int i = 1; i < n; ++i)
   ans = gcd(ans, a[i]);

cout << ans << endl;

return 0;
}

works with clang++ -std=c++17.

edited Oct 20 '18 at 13:36

answered Oct 20 '18 at 13:32

Matthieu Brucher

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This does not answer the question. – user202729 Oct 20 '18 at 13:32
Besides, the function is from c++17 only. – user202729 Oct 20 '18 at 13:33
1

Which is available on Mojave. – Matthieu Brucher Oct 20 '18 at 13:33
This code is working without error on code.hackerearth.com online compiler which uses g++ 5.4.0 – Anonymous Oct 20 '18 at 15:31

score 0 · Answer 2 · edited Mar 31 '21 at 15:25

0

int gcd(int a, int b){
    if (b == 0)
       return a;
    return gcd(b, a % b); 
}

As in my mac '__gcd()' is also not working and showing that "use of undeclared identifier' so I have to predefine this function.

edited Mar 31 '21 at 15:25

cigien

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answered Dec 20 '20 at 04:38

Aayush Shah

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score 0 · Answer 3 · answered Mar 31 '21 at 15:18

0

As the other answer says, use the standard std::gcd instead of a non-standard __gcd, if possible.

That said, the error means that __gcd only works on unsigned integers. Change the types of your variables from int to unsigned int.

answered Mar 31 '21 at 15:18

HolyBlackCat

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Why __gcd() is throwing error in macOS mojave?

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