Help and explanation on Pointers.

[MindCracker]

Hi

I am learning Visual C++ and struggling to understand what they means:
1) What is CMainFrame *mainframe = (CMainFrame *) AfxGetMainWnd();
2) mainframe->ProgressAddString(ctext);
3) What is the difference between CMainFrame *mainframe and CMainFrame* mainframe? Are they the same?? Which one is the correct way?

Can anyone please help to explain that? I read many programming boooks but still got to nowhere. Any recommended resources I could refer to ? Please help!! Thank you

 

[victorv]

Hi,

I will start from point 3.

3) they are the same; in both case, mainframe is a pointer
to an object of CMainFrame class.
The problems become when you write more than a variable in
one declaration.
Try to write a part of program that analyze the sizeof of:

CMainFrame p0 ;
CMainFrame *p1 ;
CMainFrame* p2 ;
CMainFrame *p3, *p4, p5 ;
CMainFrame* p6, p7 ;


2) Here, you simply run a function: it is a member
of the object pointed by mainframe.

1) The operator (something) is called "cast". Often,
in C++, this is only a formal problem:
mainframe and the return value of AfxGetMainWnd,
are both pointers ( 4 byte here, now ), but in the
declaration are one to CMainFrame and the other to CWnd:
whit this cast you take the responsability to put
a type in an other.

In old version of C, you can write:

int i1, *i2 ;

i1 = 5 ;
i2 = i1 ;

whithout receive error ( at compile time! ) ;


Bye

 

[MindCracker]

Dear Victor,

Thanks very much for your help. Your explanation is very clear and helpful!!! I finally got the point. Have a good day to you!

cheers,