对象数组长度的获取问题

#include <iostream>
#include <string>
using namespace std;

class Student{
public:
    Student(int n,int s){
        number  = n;
        score   = s;
    }
    void print(){
        cout<<number<<"      "<<score;
    }
private:
    int number;
    int score;
};

void cal_size(Student stu[]){
    cout<<"函数内计算的大小"<<sizeof(stu)<<"---"<<sizeof(stu[0])<<endl;
}
int main(){
    Student stu[5] = {
        Student(1,100),
        Student(2,200),
        Student(3,300),
        Student(4,400),
        Student(5,500)
    };
    cal_size(stu);
    cout <<"函数外计算的大小"<<sizeof(stu)<<"---"<<sizeof(stu[0])<<endl;
    system("pause");
    return 0;
}