Simple demo showing how X macros can be used to generate an enumeration as well as a string array mapped to that enumeration

X macros

/*
 * This demo shows how preprocessor macros (formally called X macros) can be
 * used to convert one list into both an enumeration and an array of strings.
 * This is really useful for converting an enum value into a readable form.
 *
 * Dan Collins 2015
 */
#include <stdlib.h>
#include <stdio.h>

/* The list of values we want to turn into an enum and a string array */
#define LIST_OF_STATUSES \
  X(STATUS_IDLE) \
  X(STATUS_CONNECTING) \
  X(STATUS_CONNECTED) \
  X(STATUS_DISCONNECTING) \
  X(STATUS_ERROR)


/* Create the enumeration */
#define X(name) name,
typedef enum {
  LIST_OF_STATUSES
} status_t;
#undef X

/* Create the strings mapped to the enumeration */
#define X(name) #name,
static char *status_strings[] = {
  LIST_OF_STATUSES
};
#undef X

int main(void) {
  status_t s;

  s = STATUS_IDLE;

  while (s != STATUS_ERROR) {
	switch(s) {
	case STATUS_IDLE:
	  printf("%s\n", status_strings[s]);
	  s = STATUS_CONNECTING;
	  break;

	case STATUS_CONNECTING:
	  printf("%s\n", status_strings[s]);
	  s = STATUS_CONNECTED;
	  break;

	case STATUS_CONNECTED:
	  printf("%s\n", status_strings[s]);
	  s = STATUS_DISCONNECTING;
	  break;

	case STATUS_DISCONNECTING:
	  printf("%s\n", status_strings[s]);
	  s = STATUS_ERROR;
	  break;

	default:
	  printf("You're a wizard, Harry!\n");
	  s = STATUS_ERROR;
	  break;
	}
  }

  printf("%s\n", status_strings[s]);

  return 0;
}

Thanks for the comment. I’d forgotten all about this actually - I’m not sure if I wrote this to help myself remember or as a note for someone else!My personal preference is for the strings to exactly match the enumeration - but you can absolutely do what you suggested. It may make the code harder to search - but that’s what ‘gcc -E’ is for ;)Kind regards,DanOn 12/10/2022, at 21:14, mickjc750 ***@***.***> ***@***.*** commented on this gist. Thanks! just what I was looking for. Only I'd rather the strings didn't include STATUS_ prefix. Easily fixed: Remove the STATUS_ prefix from lines 13-17, ie. X(STATUS_IDLE) to X(IDLE) Then changing line 21 from #define X(name) name to #define X(name) STATUS_##name —Reply to this email directly, view it on GitHub, or unsubscribe.You are receiving this because you authored the thread.Message ID: <dancollins/X ***@***.***>