decltype

根据表达式的类型自动推导类型

int main(void)
{
    

    decltype(x) c = 21.1; //赋值
    decltype((x)) d = c; // 是一个引用
    decltype(x) e = c; //
    d = 120;
    cout << sizeof(int) << endl;
    cout << sizeof(c) << " c=" << c << endl; // c的类型按照 x的类型进行显示
    cout << sizeof(d) << " d=" << d << endl;
    cout << sizeof(e) << " e=" << e << endl;

    return 0;
}

 

 

template <typename T, typename T2>
auto ADD(T a, T2 b) -> decltype(a+b)
{
    return a + b;
}
int main(void)
{
    int a = 10;
    int b = -5;
    double x = 10.1;
    double y = -5.1;
    cout << ADD(a, x) << endl;
}