what am i seeing : size of class ?

whacko (3)
hey,
could someone explain to me what it is that i'm seeing in the output. the 'this' pointer is 8 bytes apart between the 2 instances...:

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#ifndef STUDENT_H
#define STUDENT_H
#include <iostream>
#include <iomanip>
using namespace std;

class student{
 private:
      int hours;
      float gpa;
 public:
      student(){
            hours = 0;
            gpa   = 0.0;
            cout << "in constructor 0 : " << endl;
            cout << "hours =          : " << hours << endl;
            cout << "gpa   =          : " << gpa   << endl;
      }
      student(int h,float g){
            hours = h;
            gpa   = g;
            cout << "in constructor 1 : " << endl;
            cout << "hours =          : " << hours << endl;
            cout << "gpa   =          : " << gpa   << endl;
      }
      ~student(){
            cout << "destroying      : " << this << endl;
      }
      void addcourse(int coursehours,float grade){
            float weightedgpa;
            weightedgpa = hours * gpa;
            hours      += coursehours;
            weightedgpa+= grade * coursehours;
            gpa         = weightedgpa / hours;
      }
      void printgpa(){
            cout.setf(ios::fixed|ios::showpoint);
            cout << "Hours =         : " << hours << endl;
            cout << "GPA   =         : " << setprecision(2) << gpa << endl;
      }
};
#endif


output :
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in constructor 0 :
hours =          : 0
gpa   =          : 0
in constructor 1 :
hours =          : 4
gpa   =          : 4
Enter # of hours this term : 16
Enter gpa earned           : 4.0
Hours =         : 16
GPA   =         : 4.00
Hours =         : 4
GPA   =         : 4.00
destroying      : 2ff229b8
destroying      : 2ff229b0//huh?

i figured you don't need to see main() for this.i just don't want to make another bad assumption. thanks.
Last edited on
firedraco (6246)
Because this is a pointer to the current object. Since you are creating two objects, they are not the same, and thus they have different memory addresses.
whacko (3)
i understand that. my question is the difference in size between the instances. is this indicative of the size of the object(s)?
firedraco (6246)
I believe it is because the compilier is probably allocated them in 8 bytes increments...sort of like:

[DDDDD000][DDDDD000]
^Data ^nothing
jsmith (5804)
Well, the size of the data members of the class happens to be 8 bytes (on a 32-bit system), but you cannot make the assumption that consecutive new's of an object will yield pointers that are sizeof( classtype ) bytes apart.


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