C – 析构函数的调用次数比预期的多

class C1
{   public:

        C1(){ cout<<"CONSTR WAS HERE"<<endl; }

        C1(const C1&ob){ cout<<"COPY CONSTR WAS HERE"<<endl; }

        ~C1(){ cout<<"DESTR WAS HERE"<<endl; }
}

void f1(C1 x){  }

int main()
{
    C1 c1;
    f1(c1);
}

如果我们按原样运行代码,我们得到：

CONSTR WAS HERE
COPY CONSTR WAS HERE
DESTR WAS HERE
DESTR WAS HERE

从我的观点来看,这是完全可以理解的.但是,如果我们将函数“f1”修改为：

C1 f1(C1 x){ }

代替

void f1(C1 x){ }

我们得到：

CONSTR WAS HERE
COPY CONSTR WAS HERE
DESTR WAS HERE
DESTR WAS HERE
DESTR WAS HERE

我不太清楚为什么