Thread: What does -> mean.....

Not sure if this is the right board, but........

Recently brought "Practical Visual C++ 6", and it uses a lot of syntax like

Code:

GetDlgItem(IDC_CENTER) ->ShowWindow(bVisible ? SW_HIDE : SW_SHOW)

While I can see this is extremely efficient "function crunching", it is also "newbie unfriendly"!

So just to ensure I have got this straight, am I right in saying this is equivalent to...

Code:

button1=GetDlgItem(IDC_LEFT);
bVisible = bVisible ? SW_HIDE : SW_SHOW;
button1.ShowWindow(bVisible);

(I know the syntax may be wrong here, but it is the sense of the syntax I am trying to capture!!)

Also, am I right in saying that -> is read as "is a member function of"??

Thanks,

Rob.

Code:

GetDlgItem(IDC_CENTER) ->ShowWindow(bVisible ? SW_HIDE : SW_SHOW)

GetDlgItem() returns a pointer to a CWnd (Window wrapper).....

So with this call you have a pointer to an item from a dialog that is derived from a CWnd.....now the '->' is the same as the '.' operator that allows you access to member functions of an object that you have made an instance of.....but the '->' is used when you have a pointer to an object......so in essence you are now calling the ShowWindow() member function of CWnd.....

The "bVisible ? SW_HIDE : SW_SHOW" represents a ternary logic operator (ternary refering to the fact that it has 3 operators!)...

It means "if bVisible is true, this will be SW_HIDE....failing that it will be SW_SHOW"....

It can be rewritten as

Code:

bool bVisible;

//........whatever makes bVisible true or false

CWnd* MyWnd = NULL;
int nCommandShow;

MyWnd = GetDlgItem(IDC_CENTER);

if( bVisible == true ){
nCommandShow = SW_HIDE;
}
else{
nCommandShow = SW_SHOW;
}
MyWnd->ShowWindow(nCommandShow);

Cheers Rob,

I see (I think)!

One last thing, your example re-write used

MyWnd->ShowWindow(nCommandShow);

The real question was, is there any way to rewrite the original without using -> (as it was the -> that was confusing me).

Mind you, just asking the question helped me understand it!

Originally posted by RobR

One last thing, your example re-write used

MyWnd->ShowWindow(nCommandShow);

The real question was, is there any way to rewrite the original without using -> (as it was the -> that was confusing me).

Yes...but get used to the -> operator as you will see alot of it......

To stop using it you can derefrence the object you are calling on

Code:

*MyWnd.ShowWindow(nCommandShow);

Yes...but get used to the -> operator as you will see alot of it......

To stop using it you can derefrence the object you are calling on

Code:

*MyWnd.ShowWindow(nCommandShow);

Excellent. Many thanks.

Understand your comment about getting used to it. It's just that I like to understand things in comparison to what I already know (if you see what I mean).

Correct. Taken from boolean mathematics (George Boole, 17th century engineer i believe - may have got the century wrong, but you get the point).

Originally posted by monkeymon



bool bVisible
is it the same as the bolean in java programing ????
it only return true or false??

Yeah.......C++ allows the use of a boolean primitive variable......it can be true or false.....If I wanted to, I could have also used the WinAPI typedef BOOL

GetDlgItem(IDC_CENTER) ->ShowWindow(bVisible ? SW_HIDE : SW_SHOW)

can be rewritten as

ShowWindow( GetDlgItem(IDC_CENTER), bVisible ? SW_HIDE : SW_SHOW);

or even

ShowWindow( GetDlgItem(IDC_CENTER), bVisible);

as SW_HIDE is defined as =0 (SW_SHOW=5)

RobR,
I re-ran into the same confusion recently myself...

Fordy,
You explained that very well. You'd better be careful, Someones gonna start using terms like "Knowledgeable" when refering to you

Code:

Fordy Robr();

val = Robr->SetTitle("Knowledgeable");

Remember Robr, your only an instance.

I think you will have to use

Code:

 (*MyWnd).ShowWindow(nCommandShow);

because the . is processed first. Thats why they use the ->, all those paretheses and * get confusing fast.