>From http://www.parashift.com/c++-faq-lit...s.html#faq-8.6, it
said "Use references when you can, and pointers when you have to."

And I need to convert this java class to c++:

public class Y {
public final int[] w

public Y(final List alist {
w = new int[alist.size()];
}
}

So I am thinking about create a Reference of stl:vector for my
attribute 'w'.

class Y
{
public:
Y
virtual ~Y();

vector<int>& w;
};

and in my constructor, i initialize it like this:
Y::Y(list<Z>& alist) :
w ( vector<int>(alist.size()) )
{

}

And I get this compilation error:
.../src/YMapData.cpp:9: error: invalid initialization of non-const
reference of type 'std::vector<int, std::allocator<int> >&' from a
temporary of type 'std::vector<int, std::allocator<int> >'

I appreciate if someone can tell me what did I do wrong.

ken.carlino@gmail.com wrote:[color=blue][color=green]
>>From http://www.parashift.com/c++-faq-lit...s.html#faq-8.6, it[/color]
> said "Use references when you can, and pointers when you have to."[/color]

That's to distinguish between pointers and reference. In your case, you
simply need an object. I understand, coming from Java some folks do not
grasp that concept sometimes. You need to make an effort.
[color=blue]
> And I need to convert this java class to c++:
>
> public class Y {
> public final int[] w
>
> public Y(final List alist {
> w = new int[alist.size()];
> }
> }
>
> So I am thinking about create a Reference of stl:vector for my
> attribute 'w'.
>
> class Y
> {
> public:
> Y
> virtual ~Y();
>
> vector<int>& w;[/color]

Should simply be

vector<int> w;
[color=blue]
> };
>
> and in my constructor, i initialize it like this:
> Y::Y(list<Z>& alist) :
> w ( vector<int>(alist.size()) )[/color]

Should instead be

w(alist.size())
[color=blue]
> {
>
> }
>
> And I get this compilation error:
> ../src/YMapData.cpp:9: error: invalid initialization of non-const
> reference of type 'std::vector<int, std::allocator<int> >&' from a
> temporary of type 'std::vector<int, std::allocator<int> >'
>
> I appreciate if someone can tell me what did I do wrong.
>[/color]

You will need to learn to _instantiate_ objects.

V

Thanks.

If I change it to this:

class Y
{
public:
Y
virtual ~Y();

vector<int> w;

Do I still need to free it in Y's destructor? if yes, how? I don't do
'delete w', right since 'w' is not a pointer or reference?

And since w is a public attribute, can otherside still access it?
can a caller do this?

Y y;
cout << y.w.size() << endl;
y.w.pushback(6);
cout << y.w.size() << endl;

On 11 Jan 2006 11:48:19 -0800, ken.carlino@gmail.com wrote:
[color=blue]
>Thanks.
>
>If I change it to this:
>
> class Y
> {
> public:
> Y
> virtual ~Y();
>
> vector<int> w;[/color]

Why do you declare your constructors like that? It simply will not
compile. Try:

class Y
{
public:
Y();
virtual ~Y();
/* ... */
};
[color=blue]
>
>Do I still need to free it in Y's destructor? if yes, how? I don't do
>'delete w', right since 'w' is not a pointer or reference?[/color]

No, the data isn't dynamically allocated, so it doesn't need to be
dynamically de-allocated.
[color=blue]
>And since w is a public attribute, can otherside still access it?[/color]

Yes, but having public data in classes isn't particularly good OOP
design.

ken.carlino@gmail.com wrote:[color=blue]
> If I change it to this:
>
> class Y
> {
> public:
> Y[/color]

???
[color=blue]
> virtual ~Y();
>
> vector<int> w;
>
> Do I still need to free it in Y's destructor?[/color]

No. The destruction of a Y will cause the destruction of any members
of the Y, and the w will be freed automagically.
[color=blue]
> if yes, how? I don't do
> 'delete w', right since 'w' is not a pointer or reference?[/color]

It's not, so it will destroyed without your attention.
[color=blue]
> And since w is a public attribute, can otherside still access it?[/color]

Yes. If you're concerned with it, make it private.
[color=blue]
> can a caller do this?[/color]

Almost.
[color=blue]
>
> Y y;[/color]

Isn't there an argument?
[color=blue]
> cout << y.w.size() << endl;
> y.w.pushback(6);[/color]

The member function name is 'push_back'.
[color=blue]
> cout << y.w.size() << endl;[/color]

V

On Wed, 11 Jan 2006 20:04:08 +0000, W Marsh <wayne.marsh@gmail.com>
wrote:
[color=blue]
>On 11 Jan 2006 11:48:19 -0800, ken.carlino@gmail.com wrote:
>[color=green]
>>Thanks.
>>
>>If I change it to this:
>>
>> class Y
>> {
>> public:
>> Y
>> virtual ~Y();
>>
>> vector<int> w;[/color]
>
>Why do you declare your constructors like that? It simply will not
>compile. Try:[/color]

It won't compile when you try to define a body for the constructor,
that is. Either way, it isn't doing what you think it is doing.

On 11 Jan 2006 11:48:19 -0800 in comp.lang.c++,
ken.carlino@gmail.com wrote,
[color=blue]
> vector<int> w;[/color]

Right.
[color=blue]
>Do I still need to free it in Y's destructor?[/color]

No. The compiler automatically generates the proper call to
std::vector destructor.
[color=blue]
>And since w is a public attribute, can otherside still access it?[/color]

Yes.