cpp中sizeof与指针

一直不清楚c++的sizeof，现在通过实验得到了一些了解。

#include<iostream>

using namespace std;

class A{
private:
      char * a1;
//  !    static int totalPeople=0;  //error: ISO C++ forbids in-class initialization of non-const static member 'People::totalPeople'|
public :
      A(){
      a1 = (char *)new string ("None");
      }
};
class B{
private:
      char * b1 ;
      int b2 = 2;
};
class C:public A, B{
};
void print_boundary(){
      int screenLength = 80 ;
      char dec = '-';
      int i = 0;
      for(;i<screenLength;i++)
            {
                  cout<<dec;
            }
            cout<<flush;
}
template <typename T>
void print_pointer_info(  T * p ){
      cout<<"sizeof pointer:"<<sizeof(p)<<endl;
       cout<<"sizeof what point to:"<<sizeof( *p)<<endl;
}
int main(){
      print_boundary();
      void * p = NULL;
      A * a = new A();
      B * b = new B();
      C * c = new C();
      cout<<sizeof(p)<<endl;
      cout<<sizeof(&p)<<endl;
      print_pointer_info<A>( a);
      print_pointer_info<B>( b);
      print_pointer_info<C>( c);

}

/*

*/

运行的结果:

--------------------------------------------------------------------------------
4
4
sizeof pointer:4
sizeof what point to:4
sizeof pointer:4
sizeof what point to:8
sizeof pointer:4
sizeof what point to:12

总结:

1.对于32位的系统，指针的大小总是32位。

2.sizeof(&p)能够取得所指对象的大小，比如指针指向的是一个类的对象，那么该对象的大小仅仅是其包含的数据的大小，与有多少个函数无关。