On 31/05/2010, at 5:38 PM, David FOXWELL wrote:
I'm trying to imagine what the code would look like in RPG?
In i/o module, I hard code the equivalent of the client record to be
returned to the caller :
D ClientDS_V1 DS QUALIFIED
D Field1
The client file gets changed, so I add a new version of this DS :
D ClientDS_V2 DS QUALIFIED
D Field1
D Field2
Yes. The I/O procedure will now have two data structures defined.
Caller :
CallP GetClient_V1 ( ClientDS : Error );
No, that's just ugly. What will things look like after the fifth or
27th version?
In the called procedure, each modification of the client file would
mean duplication of the last version plus the modification. Or would
it be called like this with the version as a parameter :
CallP GetClient_V1 ( ClientDS : version : Error ); If this way, how
would you return the right DS?
This is better. You return the right structure by accepting a blob of
space (i.e., big char variable with OPTIONS(*VARSIZE) to allow large
chunks of space.
The caller provides the space, the size of the space, the format/
version of the structure, plus some sort of error field.
The I/O procedure loads the appropriate DS, based on the version/
format, internally and then copies from the DS to the caller's space
for the lesser of the DS size or as much as the caller said they
provided.
The caller can either define the DS as based and assign the address of
the DS to the big variable, or can just pass the DS itself which,
after all, is just a blob of (structured) space.
Examine any of the IBM APIs that return various structures for ideas.
QUSRJOBI would be a good example.
Thus in the caller:
D GetClient PR
D rcvVar 32767 OPTIONS(*VARSIZE)
D rcvVarLen 10I 0 CONST
D version 10I 0 CONST
D selection ???? CONST
D error ????
D rcvVar S 1000
D clientData DS LIKEDS(clientData_V2)
BASED(@clientData)
D client DS LIKEDS(clientSelection)
/free
// Populate client DS with selection criteria e.g., ID. name,
number, etc.
GetClient( rcvVar : %SIZE(rcvVar) : CLIENT_DS_V2 : client : error );
@clientData = %ADDR(rcvVar);
// do stuff with Client DS
or alternatively
D clientData DS LIKEDS(clientData_V2)
D client DS LIKEDS(clientSelection)
/free
// Populate client DS with selection criteria e.g., ID. name,
number, etc.
GetClient( clientData : %SIZE(clientData) : CLIENT_DS_V2 : client :
error );
// do stuff with Client DS
In the I/O procedure:
D GetClient PI
D rcvVar 32767 OPTIONS(*VARSIZE)
D rcvVarLen 10I 0 CONST
D version 10I 0 CONST
D selection ???? CONST
D error ????
D clientDS_V1 DS LIKEDS(clientDS_V1)
BASED(@clientDS)
D clientDS_V2 DS LIKEDS(clientDS_V2)
BASED(@clientDS)
D clientSize S 10I 0
D length S 10I 0
/free
select;
when ( version = CLIENT_DS_V1 );
clientSize = %SIZE(clientDS_V1);
when ( version = CLIENT_DS_V2);
clientSize = %SIZE(clientDS_V2);
other;
// error condition
endsl;
@clientDS = %ALLOC( clientSize );
// read the desired record using selection information
select;
when ( version = CLIENT_DS_V1 );
// populate DS version 1
when ( version = CLIENT_DS_V2);
// populate DS version 2
endsl;
if ( rcvVarLen >= clientSize );
length = clientSize;
else;
length = rcvVarLen;
memcpy( %ADDR(rcvVar) : @clientDS : length );
dealloc(n) @clientDS;
return;
/end-free
Written in e-mail without testing so there may be syntax errors but
you should get an idea of what's necessary. Actual code will vary
according to your needs.
Regards,
Simon Coulter.
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