Does it need a copy constructor and an operator= for a class which have array member
 

Does it need a copy constructor and an operator= for a class which have array member?
for example:

Class A
{
private:
B data_[100]; //B is a class
};

does class A need a copy constructor and an operator? in other words, is the default copy constructor is OK for class A?

I think if the default copy constructor/operator= can invoke copy constructor/operator= of class B, it will be OK, it's not necessary to define a copy constructor and operator=. otherwise, it's necessary.


I used Dev-C++ to test this case, I found the operator= of class B was invoked. I don't the other compilers are the same as Dev-C++. Or this is a standard of C++.

Re: Does it need a copy constructor and an operator= for a class which have array member
 

>Does it need a copy constructor and an operator= for a class which have array member?
No, the default behavior will do what you want.

Re: Does it need a copy constructor and an operator= for a class which have array member
 

Thank you for your reply.

In my example, Do you mean the default behavior is call the operator= of class B? If the default behavior is just memory copy and class B have pointer member, it will produce a undefined result.

Re: Does it need a copy constructor and an operator= for a class which have array mem
 

you can answer this yourself if you write a small test program and run it. for example:

#include <iostream>



struct A

{

  A() { std::cout << "A::default constructor\n" ; }

  A( const A& ) { std::cout << "A::copy constructor\n" ; }

  A& operator= ( const A& )

  { std::cout << "A::assignment\n" ; return *this ; }

};



struct B { A a[2] ; };



int main()

{

  B one ;

  std::cout << "-----------\n" ;

  B two(one) ;

  std::cout << "-----------\n" ;

  one = two ;

}

Re: Does it need a copy constructor and an operator= for a class which have array member
 

>In my example, Do you mean the default behavior is call the operator= of class B?
I fail to see how my reply was ambiguous. You want a member array to be properly copied even in the case where a non-default copy constructor or assignment operator exists for the array type, and that's what happens. Therefore, saying that the default behavior will do what you want is a complete answer to your question.

>If the default behavior is just memory copy and class B
>have pointer member, it will produce a undefined result.
That's strictly a quality of implementation issue for class B. If B implements a copy constructor/assignment operator then A will have to call it when copying any object of B, even if the object of B is a member of an array.

Re: Does it need a copy constructor and an operator= for a class which have array mem
 

Thank you.

In fact, I have written test program and have run a lot of test case, all those case were OK.
I just want that is a standard of C++ or just dependent on the compiler( I used Dev-C++ to compile my code).

Re: Does it need a copy constructor and an operator= for a class which have array member
 

Thank you. got it.

Re: Does it need a copy constructor and an operator= for a class which have array member
 

The use of copy constructor and overloading an assignment operator is same ( i.e. to eliminate the data loss,specially when the class has pointer members , when objects are being copied either as an argument to fuction or return from a function or initialization or copying ) ; but both have different scenarios in which they solve this problem .
A copy constrcutor is used in
[1] initialisation
[2] passing object as function argument
[3] return from a function
while assignment operator will be used in cases of explicit assignment statements.

So you should have both a copy constructor and an operator= overloaded .