data member cannot be created

[brac37]

Hello all,

I have a problem. I want some class B to create a data member of another class A. The default constructor of A is protected, so I take another constructor.

A a(8,3);

The compiler however thinks that a is a function declaration and gives an error message on its parameters. So how can I tell the compiler that a is a data member?

[hamsterman]

Where exactly is this line in your code?

[brac37]

class B
{
A a(8,3); // seen as function call
A b; // valid, but uses default constructor
}

Are there other spots where you can create data members of B?

[LB]

This exact same thing happened to me. You can't use constructors in a class like that. You need to initialize the object with the main class constructor:

struct ClassA
{
	int A, B;

	ClassA(){}
	ClassA(int a, int b){ A = a; B = b; }
};

struct ClassB
{
	ClassA MyObjA(1, 2); //Illegal, you can't use a constructor in a declaration
	ClassA MyObjB; //Legal, but to initialize it you have to do so in ClassB's constructor

	ClassB(){ MyObjB.A = 1; MyObjB.B = 2; }
};

[hamsterman]

You can also call constructors from constructor:

struct ClassB
{
    ClassA MyObjA;
    ClassA MyObjB;

    ClassB() : MyObjA(5, 7), MyObjB(3, -2){}
};

[Zhuge]

++hamsterman, initialzer lists.

[LB]

Hm, when I try to use initializer lists for file streams, my compiler explodes.

[brac37]

The constructor of B is where the constructors of members of B are chosen, instead of in the class description. Good point, hamsterman. I only knew that you can choose the constructor of the parent of B there.

struct ClassA
{
    int A, B;

    ClassA(){}
    ClassA(int a, int b){ A = a; B = b; }
};

struct ClassB : ClassA
{
    ClassA MyObjA;
    ClassA MyObjB;

    ClassB(); 
}

ClassB::ClassB() : ClassA(2,3), MyObjA(5, 7), MyObjB(3, -2){};

Maybe, you also know how to choose another constructor when using new[], but it might be that you are really condemned to the default constructor with new[].