C++ 报错 'gcd' was not declared in this scope

最近想用gcd(a, b)计算a和b的最大公约数，结果遇到如下错误：

[Error] 'gcd' was not declared in this scope

解决方法

用的时候不要忘记了__
示例：

#include <cstdio>
#include <algorithm>
using namespace std;

int main(void)
{
	int a, b;
	scanf("%d%d"， &a, &b);
	printf("%d\n", __gcd(a, b));
	return 0;
}