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In the below example, is Proc1(ptr) really passing a pointer to a pointer?
That would be bad, and if that's what is happening then that could be the
problem with the API call.
"Wilt, Charles"
<CWilt@xxxxxxxxxx
om> To
Sent by: "RPG programming on the AS400 /
rpg400-l-bounces@ iSeries" <rpg400-l@xxxxxxxxxxxx>
midrange.com cc
Fax to
01/27/2006 10:39
AM Subject
RE: CONST vs. VALUE on a pointer
parameter
Please respond to
RPG programming
on the AS400 /
iSeries
<rpg400-l@midrang
e.com>
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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