RE: RPG IV Pointers

[Joel Fritz <JFritz@xxxxxxxxxxxxxxxx>]

> -----Original Message-----
> From: Jim Langston [mailto:jlangston@conexfreight.com]
> Sent: Monday, February 28, 2000 2:52 PM
> To: RPG400-L@midrange.com
> Subject: Re: RPG IV Pointers
> 
> 
> Okay, so, can I do this?
> 
> D MyPointer                         S                              *
> D MyField                            S                        50
> C                                              Eval     
> MyPointer = %Addr(MyField)
>

Yes, you're assigning the MyPointer the address of MyField.

  
> Is that equivalent to:
> 
> D MyPointer                         S                              *
> D MyField                            S                        
> 50   Based(MyPointer)
>

Yes and no.  MyPointer needs to contain a legitimate address for you to do
anything predictable with MyField.  As long as you assign the MyPointer an
address by pointing it at another field or allocating heap memory for it
this will work.  

The difference between the two cases is that in case 1 MyField has an
address independent of the contents of MyPointer, while in case 2 the
address of MyField depends on the address contained in MyPointer.   

You can get yourself in the same trouble you can get into in C, the syntax
is just a little bit different.


> Regards,
> 
> Jim Langston
> 
> 
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