关于C中的构造函数和赋值运算符

class GreatClass
{
public:
    GreatClass(){cout<<"Default Constructor Called!n";}
    GreatClass(GreatClass &gc){cout<<"Copy Constructor Called!n";}
    GreatClass(const GreatClass &gc){cout<<"Copy Constructor (CONST) Called!n";}
    ~GreatClass(){cout<<"Destructor Called.n";}
    GreatClass& operator=(GreatClass& gc){cout<<"Assign Operator Called!";return gc;}
    const GreatClass& operator=(const GreatClass& gc){cout<<"Assign Operator (CONST) Called!";return gc;}
};

GreatClass f(GreatClass gc)
{
    return gc;
}

在main()函数中,有两个版本：

版本#1：

int main()
{
    GreatClass g1;
    GreatClass G = f(g1);
}

版本#2：

int main()
{
    GreatClass g1;
    f(g1);
}

它们都生成SAME输出：

Default Constructor Called!
Copy Constructor Called!
Copy Constructor Called!
Destructor Called.
Destructor Called.
Destructor Called.

我不明白为什么在将f(g1)分配给G时没有发生任何事情.此时调用了什么构造函数或运算符？

谢谢.