Regarding bitwise copying

[bajajv]

Hi, I am confused regarding these concepts. Please clearify.

1. Why is bitwise copying unsafe?
2. Does copy constructor does bitwise copying?
3. Is the main use of explicit copy constructor is to go for deep copying?

Thanks in advance.

[Girish Kanakagiri]

Hi, I am confused regarding these concepts. Please clearify.

1. Why is bitwise copying unsafe?
2. Does copy constructor does bitwise copying?
3. Is the main use of explicit copy constructor is to go for deep copying?

Thanks in advance.

1. bitwise copying will be unsafe, if you are putting some content on heap;
I mean dynamically allocating memory and storing value for datamember.
In this case bitwise copying is unsafe because both the pointers pointing to
same memory location. If deleting of both the pointers clears the same piece
of memory and leads to core dump.
If data members are stored on stack then bitwise copying is totally safe.

2. Default copy constructor does bitwise copying.

3. If the data members are stored on heap, as explained in 1. then
overloaded copy constructor is dealt with deep copying.

Regards,
Girish.

[weaknessforcats]

1.Why is bitwise copying unsafe?
2. Does copy constructor does bitwise copying?
3. Is the main use of explicit copy constructor is to go for deep copying?

Answer 1: The memory copied may contain objects that require a copy constructor in order to be copied. C++ does not use bitwise copy. Everything is memberwise copy.

Answer 2: C++ does not use bitwise copy. You need to understand that the memberwise copy has already been made and the copy constructors of the data members have already been called before you get to the left brace of your copy constructor. You just get to correctly copy anything not already copied correctly, like pointers.

Answer 3: Explicit constructors are just constructors that are marked to be called only by the programmer (i.e. explicitly). This has nothing to do with deep copy since an explicit copy constructor can't be called by the compiler in the first place.

Default copy constructor does bitwise copying.

3. If the data members are stored on heap, as explained in 1. then
overloaded copy constructor is dealt with deep copying.

This quote is not correct per my answers above. Also, it makes no difference where the data members are stored (stack oir heap). The same rules apply.