Question for C++ users!

Question

What is the difference, if any, between the following? (T stands for any class type.)
T t;
T t();
T t(u);
T t = u;

Please use KIS principle (removed last S)

Answer 1

Top two are default constructors, 3rd is a constructor that takes arguments and the bottom one is a copy constructor

Answer 2

T t; default initialization
T t(); function declaration
T t(u); direct initialization
T t = u; copy initialization

Thanks @hdo and @jafca.

Answer 3

1.) T t; create an object t and default constructor called.
2.) T t(); same as above;
3.) T t(u); create object t with passing a parameter u, appropriate constructor will be called.
4.) T t= u; create an object t with copy constructor called and copy constructor copies appropriate data members in object t. Note:- here u should be an object of type class T or the base class of class T if inheritance is used.

although many other situations be possible here.

Answer 4

1 and 2 are the same. 3 is constructor with arguments. 4 is copy constructor.

Answer 5

About the 2nd statement, it depends on the context where it's in. If it's in a class declaration or in global context (outside any function or class definitions) then it's function declaration. Otherwise it's a statement that instantiates an object of class T using default constructor.