RE: CL pgm and pointer variables

-----Original Message-----
From: rpg400-l-admin@midrange.com [mailto:rpg400-l-admin@midrange.com]On
Behalf Of Hans Boldt
Sent: Thursday, November 21, 2002 10:10 AM
To: rpg400-l@midrange.com
Subject: Re: CL pgm and pointer variables


>Steve Richter wrote:
>> Of course I validate input, just as an appl programmer should!  I am
being
>> minimal in  my example for the purpose of clarity. To add validatation to
>> example I describe a 3rd array could be added.  The 1st array contains
data
>> pointers to the pgm variables to be populated, the 2nd array contains the
>> field names of those variables as appears in the stdin stream received
from
>> the browser and the 3rd array contains error information retrieved when
the
>> stdin char data ( "fld1=22.5&fld2=abc+efg&...." ) could not be mapped
into
>> the data pointer addressed variable.
>>
>> I challenge you or others to show how this very important and common task
of
>> mapping data from the browser stdin stream into variables in a program
could
>> be done as directly and efficiently as can be done with data pointers.

>First, if I recall correctly, data pointers are not terribly
>efficient. (Which is just one reason why data pointers aren't put to
>more use.)

Data pointers must be more efficient than the equivalent "DecVar =
CvtCharToDec( string )".  The conversion from unstructured char string to
numeric variable has to be done and will take multiple steps to do it.  The
data pointer is best because it pushes many details below the abstraction
level the appl programmer operates at.

 d dpVar         s         *      dataptr
 d OrderQty      s        9p 2
 d StdInString   s      999a      varying

 dpVar = %SetDataPtr( OrderQty ) ;
 ParseAndExtractFromEnvString( dpVar: 'OrderQty': StdInString ) ;

>Second, the conversion of a character value to the appropriate data
>type typically involves only a single assignment anyways, for example:
>   fld1 = %dec(envvar('fld1'):7:2);
>   fld2 = envvar('fld2');
>And so not a lot of code is saved by using some common mechanism. In
>fact, if three arrays need to be set up to be able to use a common
>routine, I suspect that would require even more coding!

Your example above does not handle a char to numeric conversion error. But I
agree, your method is similar to a conversion that uses a data pointer.  The
problem with the non data pointer method is the hard coding of the data defn
of the target variable. My hypothetical:
  dpVar = %SetDataPtr( OrderQty ) ;
is error and database change proof.  Your example requires the pgmr to
correctly type the "7:2" and also find and change all its instances when the
field is expanded to "9:2" at a later date.

btw, rpg programmers too often have to use this method of hard coding of
variable attributes.  Any chance that %DataType(variableName),
%DataLength(variable), %DataPrecision(variable) built ins will be introduced
to rpg?

thank you,

Steve Richter