When There's No Room for Special Values

by Ted Holt

It's trivia time, esteemed colleagues. The LEN parameter of the PARM command, used to define parameters in CL commands, will accept up to three values. Character data types need one value in the LEN parameter. Decimal values accept one or two. (If only one is specified, the decimal variable is assumed to have zero decimal positions.) What data type allows you to specify three values in the LEN parameter?

You may use three values with the *X data type. This type is supposed to be used with IBM commands, but I don't know of any reason we mortals can't use it, too. The *X type allows the user to key either decimal data or character data into a parameter. If the parameter value consists of digits, an optional decimal point, and an optional leading plus or minus sign, the command processing passes a decimal value to the command-processing program. The size of this decimal value is defined in the second and third values of the LEN parameter. Otherwise, the keyed value is passed as a character value whose length is the first value of the LEN parameter.

Let's consider a situation in which you might need to use the *X data type. Suppose you're writing a command that includes an adjustment quantity, and you'd like the user to be able to use the special character value REVERSE. Normally you would map the special value to an unused numeric value. In the following command definition, REVERSE is converted to -999.

CMD   PROMPT('Do Something')           
PARM  KWD(ADJQTY) TYPE(*DEC) LEN(3 0) +
        SPCVAL((REVERSE -999)) MIN(1) +
        PROMPT('Adjustment quantity')

The command-processing program would normally test for the special value and carry out special processing.

PGM  PARM(&QTY)                   
                                  
DCL  &QTY     *DEC      3         
                                  
IF (&Qty *eq -999) THEN(... do something ...) 
ELSE (... do something else ...) 

But what if there is no unused value that can be substituted for the special value? Suppose all values from -999 to 999 are valid values and none can be used to represent the special value REVERSE? This is a good time to use the *X data type.

In the following command, the ADJQTY parameter may be passed as an eight-character value or a three-digit decimal value with no decimal positions. The command processor will decide which of those formats to use by examining the parameter's value.

CMD   PROMPT('Do Something')                  
PARM  KWD(ADJQTY) TYPE(*X) LEN(8 3 0) MIN(1) +
        PROMPT('Adjustment quantity')

The command-processing program will have to determine which type of value was passed from the command and act accordingly. Since the parameter value may be either decimal or character, it may not make sense to use a CL program to process the command. The following code fragment is from a command-processing program written in RPG.

D AdjStruc        ds             8                  
D   AdjChar               1      3                  
D   AdjQty                1      2p 0               
                                                    
C     *entry        plist                           
C                   parm                    AdjStruc
C                                                   
C                   if        AdjChar = 'REV'       
... REVERSE, do something
C                   else                            
... numeric, do something else using subfield AdjQty
C                   endif