一段代码输出结构不太明白

.cpp
#include
using namespace std;

class Test {
int* l;
double d;

};

int main() {
Test cs;
cout << "double =" << sizeof(double) << endl;
cout << "int* =" << sizeof(int*) << endl;
cout <<"cs ="<< sizeof cs << endl;
cin.get();
}

结果是
double =8
int* =4
cs=16
这是为什么