In c++, if I create a constructor that takes one argument which has a default value - will that serve as a default (empty) constructor?

Question

Does the following one-parameter constructor also serve as a default constructor?

class SomeClass
    {
    public:
        SomeClass(const int &a = 4);
    }

(Assuming the constructor is well defined etc.)

Thanks!

Answer 1

Yes, the definition of default constructor allows parameters as long as they have default values:

A default constructor for a class X is a constructor of class X for which each parameter that is not a function parameter pack has a default argument (including the case of a constructor with no parameters).

(from the C++1z draft)

Older phrasing:

A default constructor for a class X is a constructor of class X that can be called without an argument.

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In addition, your copy constructor will be implicitly defined as defaulted, because you haven't declared one.

There is no such thing as a "default copy constructor". But "default constructor" and "defaulted copy constructor" are meaningful.