Is there any difference between A a; and A a = A()?

Question

Is there any difference between A a; and A a = A()? Here A is a class.

Answer 1

There is a formal difference between direct initialization syntax

A a;

and copy initialization syntax

A a = A();

in that the latter allows a call of the A copy or move constructor, and requires that there is an accessible copy constructor or move constructor.

However, in practice that extra constructor call will be elided.