How can I guarantee one #define is larger than another?

Question

#define MY_CONST 20
#define OTHER_CONST 10

My code only makes sense if MY_CONST > OTHER_CONST. How can I guarantee this with the preprocessor? Is there any command like this?

#assert MY_CONST < OTHER_CONST

@SanderDeDycker In my case, the code is clearer when these values are defined separately — Anna, Jun 15 '18 at 13:53

score 15 · Accepted Answer · answered Jun 15 '18 at 13:54

15

Is there any command like this?

#assert MY_CONST < OTHER_CONST

#if OTHER_CONST >= MY_CONST
#error "Error, OTHER_CONST >= MY_CONST"
#endif

answered Jun 15 '18 at 13:54

Attersson

4,755
1
15
29

ramrunner · Answer 2 · 2018-07-10T16:20:21.050

0

as @attersson said #if will do it. (as a good habbit try to parenthesize your macros to guarantee order of evaluation for more complex expressions. this answer shows why.)

#include <stdio.h>
#define A 10
#define B 11
#if (A) > (B)
  #define RES "yes"
#else
  #define RES "no"
#endif

int
main(int argc, char *argv[])
{
        printf("is A larger? %s\n", RES);
        return 0;
}

edited Jul 10 '18 at 16:20

answered Jul 10 '18 at 16:09

ramrunner

1,362
10
20

How can I guarantee one #define is larger than another?

2 Answers2