Macro question regarding single quotes

Macro question regarding single quotes

[Richard Harvey Chapman]

I'd like to shorten-up so redundant code in a switch statement by using 
a macro for each case. The following code illustrates the problem. In 
short, is there a way to write the PARSE(a,b) macro that will work in 
the manner shown below?


Thanks,

H.

========

#include <stdio.h>

int varAB = 1;
int varFG = 2;

#define TEST1(a,b)  printf("'%c' '%c' = %d\n", *#a, *#b, var##a##b)
#define TEST2(a,b)  printf("'%c' '%c' = %d\n", #a[0], #b[0], var##a##b)

int ParseAB(void) { return(0); }
int ParseCD(void) { return(0); }
int ParseEF(void) { return(0); }

// * not allowed in case statement
#define PARSE(a,b)   case (*#a << 8) | *#b: \
                       status = Parse##a##b();     \
                       break

// ends up being literally 'a' and 'b'
#define PARSE2(a,b)   case ('a' << 8) | 'b': \
                        status = Parse##a##b();     \
                        break

int main()
{
  int status = 0;

  TEST1(A,B);
  TEST2(F,G);

  switch (('A' << 8) | 'B')
  {
  // This is what the output of the PARSE macro should be:
  case ('A' << 8) | 'B':
    status = ParseAB();
    break;

  // This is how I'd like to use the macro.
  PARSE(C,D);
  PARSE(E,F);

  default:
    status = -1;
  }

  return(0);
}

Re: Macro question regarding single quotes

[Bernd Jendrissek]

On Fri, Aug 15, 2008 at 10:38 PM, Richard Harvey Chapman
<hchapman-gcc-help@3gfp.com> wrote:
> I'd like to shorten-up so redundant code in a switch statement by using a
> macro for each case. The following code illustrates the problem. In short,
> is there a way to write the PARSE(a,b) macro that will work in the manner
> shown below?

How about something like this:

#define rhc__A 'A'
#define rhc__B 'B'
#define rhc__C 'C'
#define rhc__D 'D'
#define rhc__E 'E'
#define rhc__F 'F'
// etc.

// * not allowed in case statement
#define PARSE(a,b)   case (rhc__##a << 8) | rhc__##b: \
                     status = Parse##a##b();     \
                     break

This depends on a reasonable-sized alphabet, of course!

Re: Macro question regarding single quotes

[Richard Harvey Chapman]

Perfect! And so simple.

Thanks,

H.

Bernd Jendrissek wrote:
> On Fri, Aug 15, 2008 at 10:38 PM, Richard Harvey Chapman
> <hchapman-gcc-help@3gfp.com> wrote:
>> I'd like to shorten-up so redundant code in a switch statement by using a
>> macro for each case. The following code illustrates the problem. In short,
>> is there a way to write the PARSE(a,b) macro that will work in the manner
>> shown below?
> 
> How about something like this:
> 
> #define rhc__A 'A'
> #define rhc__B 'B'
> #define rhc__C 'C'
> #define rhc__D 'D'
> #define rhc__E 'E'
> #define rhc__F 'F'
> // etc.
> 
> // * not allowed in case statement
> #define PARSE(a,b)   case (rhc__##a << 8) | rhc__##b: \
>                      status = Parse##a##b();     \
>                      break
> 
> This depends on a reasonable-sized alphabet, of course!