RE: CONST vs. VALUE on a pointer parameter

Note:

I mis-spoke here.  With my Proc3 and the fact that proc3(data) and
proc2(ptr) were equivalent.

Actually, given the prototype of Proc3, Proc3(data) won't compile.

What I was trying to say is that given the following procedure:

P Proc3   b
D Proc3   pi
D  in          *

You can prototype it two ways:

D Proc3a  pr       extproc('PROC3')
D  in          *   value

D Proc3b  pr       extproc('PROC3')
D  in         10a

Giving you two ways to call it:
Proc3a(%addr(data)) 
Proc3b(data)

You could also simply use 
Proc3a(ptr)


The key idea is that Proc3 itself expects a pointer.
It will get a pointer if you pass a pointer variable by value, or _ANY_
variable by reference (either CONST or not).

HTH,


Charles Wilt
--
iSeries Systems Administrator / Developer
Mitsubishi Electric Automotive America
ph: 513-573-4343
fax: 513-398-1121
  

> -----Original Message-----
> From: rpg400-l-bounces@xxxxxxxxxxxx 
> [mailto:rpg400-l-bounces@xxxxxxxxxxxx] On Behalf Of Wilt, Charles
> Sent: Friday, January 27, 2006 10:39 AM
> To: RPG programming on the AS400 / iSeries
> Subject: RE: CONST vs. VALUE on a pointer parameter
> 
> CONST = pass by constant reference ( a pointer in other words)
> VALUE = pass by value
> 
> Using the following:
> D data         s       10a
> D ptr          s         *    inz(%addr(data))
> 
> D proc1        pr
> D  in                    *    const
> 
> D proc2        pr
> D  in                    *    value
> 
> D proc3        pr 
> D  in                    *
> 
> Then:
> Proc1(data) --> passes the addr of data, doesn't allow data to be
> changed
> Proc1(ptr) --> passes the addr of ptr, doesn't allow ptr to be changed
> 
> Proc2(data) --> won't compile, since the value of data is 10A and we
> said we're passes a pointer.
> Proc2(ptr) --> passes the value of ptr, ie. the addr of data. Allows
> data to be changed.
> 
> Proc3(data) --> passes the addr of data, allows data to be changed
> Proc3(ptr) --> passes the addr of ptr, allows ptr to be changed
> 
> These two calls are equivalent:
> Proc2(ptr)
> Proc3(data)
> 
> Proc1(data) is almost the same, except data can't be changed.
> 
> 
> 
> HTH,
> 
> Charles Wilt
> --
> iSeries Systems Administrator / Developer
> Mitsubishi Electric Automotive America
> ph: 513-573-4343
> fax: 513-398-1121
>   
> 
> > -----Original Message-----
> > From: rpg400-l-bounces@xxxxxxxxxxxx 
> > [mailto:rpg400-l-bounces@xxxxxxxxxxxx] On Behalf Of darren@xxxxxxxxx
> > Sent: Friday, January 27, 2006 10:09 AM
> > To: rpg400-l@xxxxxxxxxxxx
> > Subject: CONST vs. VALUE on a pointer parameter
> > 
> > 
> > I attempted to call the Qp0lGetAttr API to get the creation 
> > date of a file
> > in the IFS.  I used the following prototype.
> > 
> >      D Qp0lGetAttr     PR            10I 0 ExtProc('Qp0lGetAttr')
> >      D  path                           *   Const
> >      D  AttArrPtr                      *   Const
> >      D  BuffPtr                        *   Const
> >      D  BuffLenSent                  10U 0 Const
> >      D  BuffLenNeed                  10U 0
> >      D  BuffLenRet                   10U 0
> >      D  FollowLink                   10U 0 Value
> > 
> > 
> > The above did not work, apparently because I had used Const.  
> > The program
> > compiles fine both ways, but the API returns a -1 indicating 
> > that some kind
> > of error occurred.  I can toggle the 'path' parameter from 
> > Value to Const
> > and get it to fail, with everything else as shown below.  My 
> > reason for
> > using Const was to document that the variable being pointed 
> > to was an Input
> > only variable per the API's specs.  Can someone in the know, 
> > educate me as
> > to the different between Const and Value in this case?
> > 
> >      D Qp0lGetAttr     PR            10I 0 ExtProc('Qp0lGetAttr')
> >      D  path                           *   Value
> >      D  AttArrPtr                      *   Value
> >      D  BuffPtr                        *   Value
> >      D  BuffLenSent                  10U 0 Value
> >      D  BuffLenNeed                  10U 0
> >      D  BuffLenRet                   10U 0
> >      D  FollowLink                   10U 0 Value
> > 
> > -- 
> > This is the RPG programming on the AS400 / iSeries (RPG400-L) 
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> > 
> 
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