useanenum

Barry Schwarz 07 Sep, 09:04

Re: Increment a number in compile time macro

On Sat, 6 Sep 2008 23:54:08 -0700 (PDT), Bin Chen
 wrote:

>switch(i) {
>case 1:
>  break;
>case 2:
>  break;
>[...]
>case N:
>  break;
>
>}
>
>Now, after some time I want to add a 'case 2' between case 1 and case
>2, the result means every case number after case 2 need to be
>incremented by 1, it there a macro tricks to make life easier? Such
>as:
>
>switch(i) {
>case AUTO_INC_MACRO:
>  break;
>case AUTO_INC_MACRO:

Macros don't perform calculations.  They only perform text
substitution.  And a subsequent appearance of a macro in your code
will not have access to the result of a previous appearance.

However, you can do what you want with an enum.  Something of the form
   enum {CASE1=1, CASE2, ..., CASEN};
and change each case label to
   case CASE1:
   ...
   case CASE2:
   etc.

Later, when you want to insert a case between CASE1 and CASE2, change
you enum to
   enum {CASE1=1, CASE1A, CASE2, ..., CASEN};
and insert the new block of code immediately before the CASE2 label.

To eliminate the rampant confusion after a half-dozen insertions where
CASE6 may be 7 while CASE10 is 13, I would suggest using identifiers
that are suggestive of the function to be performed rather than their
numeric value.  Something like
   enum {INSERT=1, DELETE, EDIT, COMPUTE};
and then you could later amend it to
   enum {INSERT=1, DELETE, EDIT, PRINT, COMPUTE};