Sizeof and C++ Object Memory allocation

Hi,

I Wonder whether the 'sizeof ' operator works at compile time or run time.

I understand the C++ objet model stores the non-static data members as part of the object.When a Object is created its size is determined by using the sizeof operator.

For ex:

Class1 *obj = new Class1;

is approximately equal to (excluding constructor calling)

Class1 *obj = (Class1)malloc(sizeof(Class1));

The memory is allocated comfortably.Fine.

I also read that when there is a addition of a member in the class (Class1) the client code which instantiates the object (previous code piece for ex) must be recompiled.If the sizeof operator finds the size of Class1 at run-time it could get the correct modified size of the Class.Why it is not implemented like that?

Thanks,
Suresh.

 

I dont mean a debug.My question is related to the failure of C++ wrt Component based software.

 

Yes.If we dont recompile the Clients, they will break (because of its static size allocation done at compile time).This could have avoided by dynamically finding the size of the type at run time.

Thanks,
Suresh.

 

Yes,We must compile the Components whenever we modify its members.No problems in that.The problem is with the Clients which uses these Components, also needs to be recompiled for correct working.

Thanks,
Suresh.