construction initialization list

[bluekite2000]

I have a Matrix class derived from an Array class as followed:
Matrix(int nM, int nN)
:Array<T>(nM*nN ),mnM(nM),mnN(n N)
{
}
However, I dont want to call Array constructor if nM!=nN. In other
words, I dont want to use the initialization list.
Regards

[Victor Bazarov]

bl**********@gm ail.com wrote:

I have a Matrix class derived from an Array class as followed:
Matrix(int nM, int nN)
:Array<T>(nM*nN ),mnM(nM),mnN(n N)
{
}
However, I dont want to call Array constructor if nM!=nN. In other
words, I dont want to use the initialization list.

OK. Now we know what you *don't* want. What *do* you want [instead]?

[bluekite2000]

My question is is there another way to call Array constructor without
using the described initialization list ?

[Victor Bazarov]

bl**********@gm ail.com wrote:

My question is is there another way to call Array constructor without
using the described initialization list ?

If you don't put it into the initialiser list, it will be
default-initialised. You can always try doing

:Array<T>(nM == nN ? nM*nN : 1),mnM(nM),mnN( nN)
{
// do something about nM not being equal nN
}

V

[bluekite2000]

Actually I want to do something along the line of
Matrix(int nM,int nN)
:
{
if (nM==nN)
{
call Array constructor to alllocate memory of size nM*nN
mnM=nM;
mnN=nN;
}
else
throw exception

[Victor Bazarov]

bl**********@gm ail.com wrote:

Actually I want to do something along the line of
Matrix(int nM,int nN)
:
{
if (nM==nN)
{
call Array constructor to alllocate memory of size nM*nN
You cannot call a constructor. The only option you have is to do
all construction in the initialiser list.
mnM=nM;
mnN=nN;
}
else
throw exception

Do what I showed (allocate an array of 1 element), and inside
the body throw, it should call the d-tor of the array of 1 element
and everything would be fine.

[bluekite2000]

Actually my condition check is a little more complicated than a
ternary operator (The nM==nM is just a simplied example). That is why I
need to use the if statement.

[Andrey Tarasevich]

bl**********@gm ail.com wrote:

Actually I want to do something along the line of
Matrix(int nM,int nN)
:
{
if (nM==nN)
{
call Array constructor to alllocate memory of size nM*nN
mnM=nM;
mnN=nN;
}
else
throw exception

In this particular case you can do literally that (still in the
initializer list)

Matrix(int nM,int nN) :
Array<T>(nM == nN ? nM * nN : throw <your exception>),
mnM(nM), mnN(nN)
{}

There's no other way to do that, unless your 'Array<T>' class provides
facilities for "postponed initialization" , i.e. default constructor +
member functions for post-construction memory allocation.

--
Best regards,
Andrey Tarasevich

[Julián Albo]

bl**********@gm ail.com wrote:

Actually my condition check is a little more complicated than a
ternary operator (The nM==nM is just a simplied example). That is why I
need to use the if statement.

You can do something like that:

class ArrayCheck {
public:
ArrayCheck (int nM, int nN)
{
if (nM != nN)
throw something;
}
};

Matrix(int nM, int nN) :
ArrayCheck (nM, nN),
Array<T>(nM*nN) ,mnM(nM),mnN(nN )
{
}
--
Salu2

[Andre Kostur]

bl**********@gm ail.com wrote in news:1113002116 .576152.3790
@l41g2000cwc.go oglegroups.com:

Actually my condition check is a little more complicated than a
ternary operator (The nM==nM is just a simplied example). That is why I
need to use the if statement.

Hmm... the base class must be completely constructed before the subclass's
constructor body can be entered. Perhaps a factory function might be more
appropriate for what you want to do?