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Exactly, You're passing a pointer to a pointer. 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 10:50 AM > To: RPG programming on the AS400 / iSeries > Subject: RE: CONST vs. VALUE on a pointer parameter > > 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) > > mailing list > > To post a message email: RPG400-L@xxxxxxxxxxxx > > To subscribe, unsubscribe, or change list options, > > visit: http://lists.midrange.com/mailman/listinfo/rpg400-l > > or email: RPG400-L-request@xxxxxxxxxxxx > > Before posting, please take a moment to review the archives > > at http://archive.midrange.com/rpg400-l. > > > > > > -- > This is the RPG programming on the AS400 / iSeries (RPG400-L) > mailing list > To post a message email: RPG400-L@xxxxxxxxxxxx > To subscribe, unsubscribe, or change list options, > visit: http://lists.midrange.com/mailman/listinfo/rpg400-l > or email: RPG400-L-request@xxxxxxxxxxxx > Before posting, please take a moment to review the archives > at http://archive.midrange.com/rpg400-l. > > > > -- > This is the RPG programming on the AS400 / iSeries (RPG400-L) > mailing list > To post a message email: RPG400-L@xxxxxxxxxxxx > To subscribe, unsubscribe, or change list options, > visit: http://lists.midrange.com/mailman/listinfo/rpg400-l > or email: RPG400-L-request@xxxxxxxxxxxx > Before posting, please take a moment to review the archives > at http://archive.midrange.com/rpg400-l. > >
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