C隐式调用函数何时？如何？

Are all functions inside of a class
member functions? or only the ones
preceded by the declaration “friend”?

朋友功能不是成员函数.它们与常规全局函数的不同之处在于它们可以访问该类的非公共区域.例如：

class myclass
{
    friend void fun(const myclass& obj);
    int x;
};

void fun(const myclass& obj)
{
    std::cout << obj.x; // x is private member
}

What is the difference between an
implicit and explicit call?

使用()运算符调用函数时,它是显式调用.如果你不这样做,那就是隐含的.显式调用的示例：

fun();

隐式调用的示例：

void someScope(){
    myclass myobject; // constructors called

} // destructor of myobject is called before exiting the function
....
myclass* mySecondObject = new myclass; // constructor called
delete mySecondObject; // destructor called