What is a non-trivial destructor in C++?

Question

I was reading this which mentions destructors being trivial and non-trivial.

A class has a non-trivial destructor if it either has an explicitly defined destructor, or if it has a member object or a base class that has a non-trivial destructor.

In example, I have a class,

class C {
    public:
     ~C(); // not explicitly declared.
};

If C::~C() is implicitly defined does it make a trival dtor?

Answer 1

You are getting your words mixed up. Your example does indeed declare an explicit destructor. You just forget to define it, too, so you'll get a linker error.

The rule is very straight-forward: Does your class have an explicit destructor? If yes, you're non-trivial. If no, check each non-static member object; if any of them are non-trivial, then you're non-trivial.

Answer 2

So you mean, the entire declaration of C is this:

class C { };

?

Then, yes: Since C has no member objects and no base classes, it therefore has no member objects with non-trivial destructors and no base classes with non-trivial destructors, so its implicitly-defined destructor is a trivial one.

Answer 3

I think in general it refers to a destructor that actually does something such as:

• Release memory
• Close a connection to database
• Or take care of any resource that needs to be released

In this case the destructor does nothing. According to the description, technically it may be 'non-trivial' because it defines a constructor, but it matters not, since it does nothing anyway.