((serverDlg*)m_pDlg)->OnReceive(port);

I built a server using MFC, and had to get the foundation going by using examples online. The OnReceieve(port), is a function that I created in my CDialog class.

((serverDlg*)m_pDlg) is the part I don't get. This line of code is in a function in my socket class, and I am able to call a function that is declared in my CDialog class(OnReceieve(port)). serverDlg is the name of my CDialog class and m_pDlg is a pointer to a CDialog object if that helps. Thanks.

CDialog is the class name of a generic dialog class. serverDlg is a class that was derived from CDialog. So if m_pDlg was declared like this: CDialog* m_pDlg; then later assigned to a pointer of type serverDlg then the line you are confused about is typecasting m_pDlg from CDialog to serverDlg so that it can call the OnReceive() method. The typecasting would not have been necessary had m_pDlg been declared as type serverDlg instead of CDialog.

Ok, I understand for the most part, but I dont get how what you just explained translated into ((serverDlg*)m_pDlg)->OnReceive(port);

I don't understand the use of the dereference operator. And I thought type casting was taking a data type such as int var1, and going char var2 = (char)var1.

Edit: You changed your profile picture as i refreshed the page =D

Edited 6 Years Ago by LevyDee: n/a

The deference operator is used because m_pDlg is a pointer and it needs to be dereferenced to access the object at this location.

If the OnReceive method belongs to CDialog and m_pDlg is a CDialog, then you don't need to cast to ServerDlg.

The typecast is needed to convert m_pDlg from CDialog to serverDlg. And as ^^^ explained.

Edited 6 Years Ago by Ancient Dragon: n/a

From looking at the line of code in question:

((serverDlg*)m_pDlg)->OnReceive(port);

If typecasting is required, shouldn't one of the C++ cast operators like dynamic_cast be used to safely typecast the pointer, instead of doing a potentially unsafe C-style cast?
e.g.

// attempt to cast m_pDlg using dynamic_cast
serverDlg *pSrvDlg = dynamic_cast<serverDlg*>(m_pDlg);

// if we've got a valid pointer, call the OnRecieve function
if(pSrvDlg)
    pSrvDlg->OnRecieve(port);
else
    // Some code here to handle the eventuality that m_pDlg
    // could not successfully be cast from CDialog* to serverDlg*

If there's any possibility that m_pDlg could point to a different CDialog based class, using dynamic_cast would be critical to avoid a runtime error/segfault in cases where m_pDlg points to a different type of CDialog derived object.

However, if you 100% know that the object pointed to by m_pDlg will only ever be a serverDlg object, then perhaps you should change the type of m_pDlg at declaration to be a serverDlg pointer rather than a CDialog pointer, which would then completely negate the need to typecast.

That's my two pence on the matter!
Cheers for now,
Jas.

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