initializing member arrays

[Klaus Rudolph]

Hi all,

I have 2 classes, the second one should include an
array of the first on. The first class should not have a default
constructor. How could I use an array of the first classes?
If it is impossible to initialize the array before entering the
constructor , it
would never be possible to use arrays of classes in C++ whitout using a
default constructor.
Is that correct?



class A {
protected:
int a;
public:
A(int _a): a(_a) {}
};

class B {
protected:
A arr[2];
public:
B(int _a1, int _a2): arr(??????????? ??) {} //<-------------------
};

int main() {
B b(1,2);
return 0;
}

The marked line is my problem. Is there no way to initialize the array?
Is using a vector<> the only solution here?

Regards
Klaus

[Ron Natalie]

Re: initializing member arrays


"Klaus Rudolph" <lts-rudolph@gmx.de> wrote in message news:4006DA5E.E ED0B518@gmx.de. ..[color=blue]
> Hi all,
>
> I have 2 classes, the second one should include an
> array of the first on. The first class should not have a default
> constructor. How could I use an array of the first classes?[/color]

Can't be done. Arrays are half-baked types in C++. This is
one of their failings. Your choices are to set the values in the
body of the constructor, or to replace it with a type (like vector)
that has reasonable initialization semantics.

[David Fisher]

Re: initializing member arrays

"Klaus Rudolph" <lts-rudolph@gmx.de> wrote:
[color=blue]
> class A {
> protected:
> int a;
> public:
> A(int _a): a(_a) {}
> };
>
> class B {
> protected:
> A arr[2];
> public:
> B(int _a1, int _a2): arr(??????????? ??) {} //<-------------------
> };
>
> int main() {
> B b(1,2);
> return 0;
> }
>
> The marked line is my problem. Is there no way to initialize the array?
> Is using a vector<> the only solution here?[/color]

You could create a protected default constructor for class A, and make B a
friend of A ... you might also want an init() function which acts as a
constructor in this case (unless you are happy to initialise arr[] with
assignments to temporary objects which use the non-default constructor).

David F

[Jerry Coffin]

Re: initializing member arrays

In article <4006DA5E.EED0B 518@gmx.de>, lts-rudolph@gmx.de says...[color=blue]
> Hi all,
>
> I have 2 classes, the second one should include an
> array of the first on. The first class should not have a default
> constructor. How could I use an array of the first classes?
> If it is impossible to initialize the array before entering the
> constructor , it
> would never be possible to use arrays of classes in C++ whitout using a
> default constructor.
> Is that correct?[/color]

Yes, it is.

[ ... ]
[color=blue]
> The marked line is my problem. Is there no way to initialize the array?
> Is using a vector<> the only solution here?[/color]

It may not be the only one but it's almost certainly the preferred one.

--
Later,
Jerry.

The universe is a figment of its own imagination.