Calling default constructor

问题

I have a problem with a default constructor in C++. It's a simple thing but can't see what's wrong with it.

I have a constructor with 3 optional parameters, with const values on initialization list:

data::data(int D = 1, int M = 1, int Y = 1583) : Day(D), Month(M), Year(Y)  
{  
    if (!CorrectDate()) throw "Wrong Date!";  
}  

Why can I call it with one, two or three parameters and it works just fine but doesn't when I call it with no parameters?

data tommorrow();

回答1:

data tomorrow(); is a declaration of a function that returns a data and takes no parameters. To create a data object with no explicit constructor arguments, just do data tomorrow; without the parentheses.

回答2:

Define it as

data tomorrow;

data tomorrow(); is the same as defining a function called tomorrow which returns data

回答3:

You are probably doing something like

data something();

which is not an initialization of a variable of type data called something, but the declaration of a function called something that returns data.

If this is the case, the correct would be:

data something;

回答4:

You are declaring a function which returns a data, you can do either:

data tommorow;

Without (), or you can do:

data tommorow = data();

来源：https://stackoverflow.com/questions/5385675/calling-default-constructor