RPG IV Comment Blocks

Hey, Ted:

Conditional compilation directives (/IF DEFINED) have two good uses that I have not seen mentioned in any of the midrange-oriented e-mail newsletters. Maybe you would like to tell your readers who work in RPG shops about them.

One good way to use a conditional compilation directive is to comment-out large sections of source code. Here's an example.

 /if defined(TheFollowingIsCommentedOut)
C                    eval      *in21 = *on
C                    eval      *in22 = *off
C*                   eval      *in23 = *on
C                    if        *in24
C                    exsr      DoSomething
C                    exsr      DoSomethingElse
C                    endif
 /endif

I prefer this technique to that of commenting out each line individually. For one thing, it's quicker to insert two lines of compiler directives than to key an asterisk (*) into column 7 of a lot of lines. Another thing I like is that I won't accidentally remove the asterisk in column 7 of the third line if I have to reactivate this section of source code at a later date.

I also like to use conditional compilation directives when including blocks of documentation in my source code. The following section of source code explains the meanings of the values of a customer invoicing option field.

  /if defined(TheFollowingIsAComment)

   Invoicing options:

     Generate the appropriate type of invoice
     according to the invoicing option code.

     E - email
     F - fax
     I - mail
     X - do not send an invoice to the customer

  /endif

You can use the full source line for documentation with this approach, but the source code editor may not like it. SEU will not complain if the comments start in column 8 or after.

Each of these examples works because I never define conditions called TheFollowingIsAComment or TheFollowingIsCommentedOut. Any series of characters, even garbage, works as long as no condition is defined by that name. Worrywarts may prefer to undefine the condition to be sure.

 /undefine TheFollowingIsCommentedOut
 /if defined(TheFollowingIsCommentedOut)

--Cletus the Codeslinger

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