API Receiver Variable Size Optimization

[bvining@xxxxxxxxxxxx]

Nothing fancy, but here is an example using the Retrieve Language IDs
API.  This API retrieves a list of language identifiers and you really
don't know for sure how many language identifiers there may be for any
given release.  So we call the API once to determine how many bytes of
data are available, allocate that size of storage, call the API again,
and then display each of the languages just to show we got there OK.
Note that the real processing is done with Based data structures.

Bruce

     DQLGRTVLI         pr                  EXTPGM('QLGRTVLI')
     D                                1    OPTIONS(*VARSIZE)
     D                               10i 0 CONST
     D                                8    CONST
     D                               10i 0 CONST
     DBaseRcv          ds
     D BytAvl                        10i 0
     D BytRtn                        10i 0
     DRealRcv          ds                  based(RealRcvPtr)
     D RBytAvl                       10i 0
     D RBytRtn                       10i 0
     D NbrLng                        10i 0
     D TextCCSID                     10i 0
     D OffLngIDs                     10i 0
     DLngInfo          ds                  based(OffPtr)
     D LngID                          3
     D LngText                       40
     DErrCod           ds
     D BytPrv                        10i 0 inz(0)
     DRealRcvPtr       s               *
     DOffPtr           s               *
     DLenRcv           s             10i 0
     DFormat           s              8    inz('RTVL0100')
     C                   call      'QLGRTVLI'
     C                   parm                    BaseRcv
     C                   parm      8             LenRcv
     C                   parm                    Format
     C                   parm                    ErrCod
     C                   alloc     BytAvl        RealRcvPtr
     C                   call      'QLGRTVLI'
     C                   parm                    RealRcv
     C                   parm      BytAvl        LenRcv
     C                   parm                    Format
     C                   parm                    ErrCod
     C                   eval      OffPtr = RealRcvPtr + OffLngIDs
     C                   do        NbrLng
     C     LngInfo       dsply
     C                   eval      OffPtr = OffPtr + 43
     C                   enddo
     C                   eval      *inlr = '1'
     C                   return
>
>The System API Programming manual for V4R1 suggests a technique for =
>optimizing storage allocation when establishing receiver variable sizes =
>as shown at the following address ...  =
>http://publib.boulder.ibm.com/cgi-bin/bookmgr/BOOKS/QB3AVC00/2.7.1
>The following is an extract from that page of the manual ...
>---QUOTE-----------------------------------------------------------------=
>
>Depending on the capabilities of your high-level language, some API =
>users take advantage of the following technique to avoid guessing the =
>appropriate size for the receiver variable:=20
>
>  1.. Call the API with a receiver variable length of 8 bytes (that is, =
>just enough for the bytes available and the bytes returned fields).=20
>  2.. Dynamically allocate an amount of storage equivalent to the bytes =
>available.=20
>  3.. Set the length of receiver variable parameter to the amount of =
>storage allocated.=20
>  4.. Pass the address of the storage allocated in step 2 by using pass =
>by value (directly).=20
>
>
>This technique provides for highly flexible use of APIs that can return =
>variable amounts of data.=20
>----END QUOTE =
>----------------------------------------------------------------
>Step one is clear enough, however, steps 2,3,4 are not.  Is this =
>technique applicable to RPG/IV ?  If not then what ?
>


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