functions within a class

[n4nature]

class A
{
  int a
public:
  get_a();
  set_a();
}

The sizeof(A) = 4 bytes.

Where are the functions stored in a class? Why does the sizeof(A) does not reflect with the memory of function definitions?

[jsmith]

Because in C, the size of a structure is the sum of the sizes of the data members (plus padding), and structs could not have member functions.

In C++ the same rule therefore applies, except that virtual functions add additional overhead due to the vtable pointer(s).

(And before you try, you cannot do sizeof( A::get_a ) to try to determine the executable code size of the function.)

[n4nature]

So where are the member functions stored? Obviously classes should have some knowledge about their locations.

[writetonsharma]

member functions are not stored anywhere. their definitions are stored in the binary/executable. when you compile/link at that time the binding of the addresses takes place. so the calling function has the address thats it. taking your example:

class A
{
  int a
public:
  get_a() //definations are generated in binary, lets say it is stored at address
{}          //0x1000
  set_a() //lets say this is stored at address 0x2000
{}
};

void main()
{
A a; //here it will take 4bytes
now if you call any function then
the code flow has the address of the called function
a.set_a(); //this will bind to 0x2000 during compilation/linking
/**
when this code point is reached during binary execution,
code will start to execute from address 2000
actually these address are resolved when the binary is loaded in the memory.
i may not be very clear, hope you might get what im saying
*/
so function address doesnt needs to be stored in class object


}

[writetonsharma]

study this and you will understand:

http://en.wikipedia.org/wiki/Call_stack