Basic Question from newbie... - Copy Constructors

Hi everyone,

First post on this forum so hope this is in the right place, please advise if not.

I'm relatively new to C++ and have been trying to test my knowledge with some online tests. I'm a little stuck on one question about copy constructors and in exactly what situations they are invoked, can anyone shed any light on which of the following they are used:


1 - When an existing object is assigned an object of its own class
2 - When a function receives as an argument, an object of the class by value
3 - When no conversion function exists for converting the class to another class object
4 - When a function returns an object to the class by value
5 - When creating an object and initialising it with an object of its own class


I think it would be in called in 2 and not in 4 but other than that I'm unsure, any help appreciated!

Thanks!

"A copy constructor is a special constructor in the C++ programming language used to create a new object as a copy of an existing object."

Wikipedia

My guess would be 5.

Thanks for the reply Skizmo, it can be more than one of those options, up to three I think...

I thought that when an object was passed by value a copy of it was made, hence 2.

Would agree with you about 5 though!

1) would use an assignment operator.
2) Yes, passing by value means creating a new object and copying the value.
3) This would be a cast operator
4) Returning by value means returning a new (temporary) object which is constructed and copied at the end of the function.
5) yes, duh.

Great, so it's 2,4 and 5. Thanks for your help!

Be careful about (1). Sometimes the assignment operator is implemented in terms of the copy constructor. That isn't automatic though.