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Asked: 2026-06-07T23:47:27+00:00

I have a class that that where I implemented my own constructor, destructor, copy

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I have a class that that where I implemented my own constructor, destructor, copy constructor
and copy assignment operator.

The class has a core set of members that I have in all of the the above and a set of “state variables” that I added as helpers for some of the methods.

These state variables are never (just because I didn’t bother doing it) initialized in the constructor but are initialized before being used.

As such the copy constructor and copy assignment do nothing with them. They just copy the members that I explicitly want.

  • Can this be a problem?
  • What happens to members that aren’t explicitly copied (btw, no pointers in these members)?
    • they are also not initialized in the constructor
  • Can this lead to any “hidden” problems?

Cheers
André

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1 Answer

  1. Editorial Team

    If those variables are part of the state of the object, then they should be copied. If the variables are not part of the state of the object, they should not be members. A variable is part of the state of the object if the outcome of any function in the interface depends on the value of that variable before the operation starts.

    There are few exceptions to the general rule above, in particular there are a few member variables that do not take part on the state of the object (they are usually marked as mutable) as synchronization mechanisms or caches for results from complex operations.

    Going back to your problem, from the description it seems that you might be using those members only as a communication mechanism between different member functions. One function in the interface sets the values and then calls other functions that read/modify them. If that is the case, consider passing the variables to the functions as arguments. By using members you are effectively hiding the dependency of the functions towards those values, and at the same time adding a dependency to the class.

    This will be much worse if any of the functions in the interface access those members, in which case after the assignment (or copy construction) the source and destination will behave differently, which breaks the assumption that after copy-initialization/assignment the source and destination objects are equivalent.

    Basically, from a practical point of view, if those members are not part of the state of the object, you might get away with your current approach, but I would really reconsider the design. If they do take part in the state of the object, you should not by any means avoid copying them.

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