Instantiate (Constructor) syntax problem.

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MilanB - 08 Jul 2006 20:22 GMT

Hello
I new to intantiate following array:
CString (**newArray)[2]

I tried following syntax, by fail.
int count = 10;
CString (**newArray)[2] = new (CString*[2])[count];

How to write correct syntax?

Thanks
Milan

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Doug Harrison [MVP] - 09 Jul 2006 04:11 GMT

>Hello
>I new to intantiate following array:
[quoted text clipped - 5 lines]
>
>How to write correct syntax?

On the LHS, you have declared a pointer to a pointer to CString[2]. This
means the RHS should create an object of type CString (*)[2] or an array of
such objects:

// Scalar
CString (**p)[2] = new (CString (*)[2]);
// Array
CString (**q)[2] = new (CString (*[count])[2]);

For these complex mixtures of pointer and array types, typedef can be your
best friend, and you can define a series of typedefs that culminate in the
type you're really after. For example, this is equivalent to the above but
a lot simpler to deal with:

typedef CString CString2[2];
typedef CString2* CString2P;
// Scalar
CString2P* p = new CString2P;
// Array
CString2P* q = new CString2P[count];

It may not make the end result any easier to understand, but at least it
was easier to get there. :)

Signature

Doug Harrison
Visual C++ MVP

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MilanB - 09 Jul 2006 08:55 GMT

Thanks Doug

Your post is very usefull.

Thanks again
Milan

> >Hello
> >I new to intantiate following array:
[quoted text clipped - 29 lines]
> It may not make the end result any easier to understand, but at least it
> was easier to get there. :)

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MilanB - 09 Jul 2006 11:26 GMT

Doug,

If I have have declared a pointer to CString[2]. How to create object of
CString[2] (syntax):

For example:
CString (*llv)[2] = new CString[2]; //Here fail right side

Thanks a lot
Milan

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Doug Harrison [MVP] - 09 Jul 2006 23:34 GMT

>Doug,
>
[quoted text clipped - 3 lines]
>For example:
>CString (*llv)[2] = new CString[2]; //Here fail right side

The expression:

new CString[2]

creates an array of two CStrings and returns a pointer to its first
element; this pointer has type CString*, as is the case for any array
CString[n]. So if your RHS is correct, you need:

CString* llv = new CString[2]; // Fine

On the other hand, if your LHS is correct, you're talking about a pointer
to an array of two CStrings, which is different, because the thing pointed
to is a CString[2], not a CString. Pointers to arrays come into play when
dealing with 2D arrays. For example:

CString (*llv)[2] = new CString[2][2]; // Fine
CString (*llv)[2] = new CString[3][2]; // Fine
CString (*llv)[2] = new CString[4][2]; // Fine

Here, new[] returns a pointer to the first element of an array
CString[m][2]. This element has the type CString[2], and so a pointer to it
has the type CString (*)[2].

In plain English, what type are you trying to create?

Signature

Doug Harrison
Visual C++ MVP

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MilanB - 10 Jul 2006 07:19 GMT

Thanks Doug,

I have already solved my problem using your previous answer. I just was
experimenting, and was not sure about my second question ( could not found
answer on web and documentation, so I asked you)

Thanks again for your very, very usefull and precise answers.
Milan

> >Doug,
> >
[quoted text clipped - 28 lines]
>
> In plain English, what type are you trying to create?

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Instantiate (Constructor) syntax problem.

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