Re: CArray::GetData

From:

=?Utf-8?B?QWw=?= <Al@discussions.microsoft.com>

Newsgroups:

microsoft.public.vc.mfc

Date:

Mon, 17 Mar 2008 12:48:35 -0700

Message-ID:

<36294D1A-3C3D-46E2-956E-8DCC9073F824@microsoft.com>

The error comes when compiling the code. It does not register

CBox* pb = (CBox*)m_Tubes.ElementAt(2).m_Box.ElementAt(3). ?GetDatat()?;

the GetData() when the code is like above. The CArray example that you have
on the bottom, had to know if I wanted Name or Num to find what I wanted.

ASSERT( box->Name == _T("Box1") );
ASSERT( box->Num == 10 );

Looking at your code, it looks to me, that using the std::vector method
would work better when adding data out of an array (that is in an array), to
a list control while adding a pointer from the array with each of the list
control items. Correct?

Also when I applying vector to my code it wants;
std::vector<Typename _Ty, typname _Ax = allocator<Ty>>;
but in your code, you have
std::vector<Box> Boxes;

can you explain the difference?

And I want to thank you for the examples, it was very helpful.
--
Just Al

"Giovanni Dicanio" wrote:

"Al" <Al@discussions.microsoft.com> ha scritto nel messaggio
news:9B5A7717-F4E2-4AF3-AD2B-E5D5EFD2BFCE@microsoft.com...

I am trying to get a pointer from an object that is of CArray but it is
also
in another CArray.

[...]

CBox* pb;

pb = (CBox*) m_tub.ElementAt(0).m_box.GetData();

doesn't get me the right array element of CBox

if I try
pb = (CBox*)m_tube.ElementAt(0).m_box.ElementAt(1).GetData();
I get an error. Is there some other way?

You did not specify what kind of error you get, the exact error message,
etc.

However, I must confess that I prefer STL containers to MFC ones (but I
prefer CString instead of std::string), especially for "composibility", i.e.
STL containers seem to behave very well when you compose them, this is not
true (at least, IMHO) for MFC containers.

So, I would suggest you to use std::vector.

I tried this code, and it compiles and works fine:

<code>

class Box
{
public:
    Box()
        : Num(0)
    {
    }

    Box( LPCTSTR name, int num )
        : Name( name ), Num( num )
    {

    }

    CString Name;
    int Num;
};

class Tube
{
public:
    Tube()
    {

    }

    CString Name;
    std::vector< Box > Boxes;
};

void TestVector()
{
    std::vector< Tube > Tubes;

    Tube tube1;
    tube1.Name = _T("Tube #1");
    tube1.Boxes.push_back( Box( "Box1", 10 ));
    tube1.Boxes.push_back( Box( "Box2", 20 ));

    Tube tube2;
    tube2.Name = _T("Tube #2");
    tube2.Boxes.push_back( Box( "Box3", 30 ));

    Tubes.push_back( tube1 );
    Tubes.push_back( tube2 );

    const Box * box = &(Tubes.at(0).Boxes[1]);

    ASSERT( box->Name == _T("Box2") );
    ASSERT( box->Num == 20 );

}

</code>

Note that I tried a similar code using CArray, but I got this compiler
error:

<error>

Error 1 error C2248: 'CObject::operator =' : cannot access private member
declared in class 'CObject' j:\programmi\microsoft visual studio
9.0\vc\atlmfc\include\afxtempl.h

</error>

Maybe to solve that kind of problem I should define a custom implementation
of some global helper function for CArray, like CopyElements...
But I find that to be a useless complexity, and IMHO a technical blunder in
definition and implementation of CArray.

For the curious ones, this is the CArray based code, giving the
aforementioned error:

<code>
class CBox
{
public:
    CBox()
        : Num(0)
    {
    }

    CBox( LPCTSTR name, int num )
        : Name( name ), Num( num )
    {

    }

    CString Name;
    int Num;
};

class CTube
{
public:
    CTube()
    {

    }

    CString Name;
    CArray< CBox > Boxes;
};

void TestCArray()
{
    CArray< CTube > Tubes;

    CTube tube1;
    tube1.Name = _T("Tube #1");
    tube1.Boxes.Add( CBox( "Box1", 10 ));
    tube1.Boxes.Add( CBox( "Box2", 20 ));

    CTube tube2;
    tube2.Name = _T("Tube #2");
    tube2.Boxes.Add( CBox( "Box3", 30 ));

    Tubes.Add( tube1 );
    Tubes.Add( tube2 );

    const CBox * box = (const CBox *)Tubes.ElementAt(0).Boxes.GetData();

    ASSERT( box->Name == _T("Box1") );
    ASSERT( box->Num == 10 );

}
</code>

Giovanni