Declaring objects of the class

[enemy]

Hello!
Please, we declared the objects in main:

  #include <iostream>
using namespace std;

class Rectangle {
    int width, height;
  public:
    void set_values (int,int);
    int area () {return width*height;}
};

void Rectangle::set_values (int x, int y) {
  width = x;
  height = y;
}

int main () {
  Rectangle rect, rectb;
  rect.set_values (3,4);
  rectb.set_values (5,6);
  cout << "rect area: " << rect.area() << endl;
  cout << "rectb area: " << rectb.area() << endl;
  return 0;
}

Can we do it and/or in line 10:

#include <iostream>
using namespace std;

class Rectangle {
    int width, height;
  public:
    void set_values (int,int);
    int area () {return width*height;}
}rect, rectb;

void Rectangle::set_values (int x, int y) {
  width = x;
  height = y;
}

int main () {
 // ? Rectangle rect, rectb;
  rect.set_values (3,4);
  rectb.set_values (5,6);
  cout << "rect area: " << rect.area() << endl;
  cout << "rectb area: " << rectb.area() << endl;
  return 0;
}

Many thanks!!!

[Peter87]

Both programs works. The difference is that in the second code rect and rectb are global variables and in the first code they are local variables in main().

[enemy]

Hello!
If they are global in first case, so as uninitialised, they are put into bss memory, then when they get initialised, they are in data memory?
What happens with their & and values in any case?

Many thanks!

[Peter87]

I'm not sure about the exact implementation details but the C++ standard guarantees that in the second code the memory of rect and rectb are zero initialized.

[enemy]

#include <iostream>
using namespace std;

class Rectangle {
    int width, height;
  public:
    void set_values (int,int);
    int area () {return width*height;}
}rect;

void Rectangle::set_values (int x, int y) {
  width = x;
  height = y;
  cout<<&rect<<" a"<<endl;
}

int main () {
  Rectangle rect;
  cout<<&rect<<" b"<<endl;
  rect.set_values (3,4);
  //rectb.set_values (5,6);
  cout << "rect area: " << rect.area() << endl;
  //cout << "rectb area: " << rectb.area() << endl;
  return 0;
}



Output:

1
2
3

	

0xbf559364 b
0x8050b38 a
rect area: 12

So, first and second &rect are obviously not at the same part of the memory???

[enemy]

Hello!
This was made by codepad (online compiler).
I suppose, first (uninitialised) rect.widht and rect.height are in bss pat of memory,

and second (initialised) rect.width and rect.height are in data.

It means, we acutally have 2 variables with the same name, (rect.width first and second) but each one has different adress and different value.

Am I right?

#include <iostream>
using namespace std;

class Rectangle {
  public:
    int width, height;
  public:
    void set_values (int,int);
    int area () {return width*height;}
}rect/*, rectb*/;

void Rectangle::set_values (int x, int y) {
  width = x;
  height = y;
  cout<<&rect<<" a"<<endl;
}

int main () {
  cout<<endl<<endl;
  Rectangle rect/*,rectb*/;
  cout<<&rect<<" b"<<endl<<rect.width<<endl<<rect.height<<endl;
  rect.set_values (3,4);
  cout<<endl<<endl<<endl<<"After being initialised: "<<rect.width<<","<<rect.height<<endl;
  //rectb.set_values (5,6);
  cout << "rect area: " << rect.area() << endl;
  //cout << "rectb area: " << rectb.area() << endl;
  return 0;
}



Output:

1
2
3
4
5
6
7
8
9
10
11

	



0xbf8d837c b
134539157
134539008
0x8050bf8 a



After being initialised: 3,4
rect area: 12