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  1. #include <stdint.h>
  2. #include <stdio.h>
  3. #include <stddef.h>
  4.  
  5. struct threshold_t {
  6.   uint8_t upper;
  7.   uint8_t lower;
  8. };
  9.  
  10. struct threshold_abc_t {
  11.   struct threshold_t a;
  12.   struct threshold_t b;
  13.   struct threshold_t c;
  14. };
  15.  
  16. static void print(const struct threshold_abc_t * const thresholds) {
  17.   printf("{\"a\": {\"lower\": %u, \"upper\": %u},\n"
  18.          " \"b\": {\"lower\": %u, \"upper\": %u},\n"
  19.          " \"c\": {\"lower\": %u, \"upper\": %u}}\n",
  20.     thresholds->a.lower, thresholds->a.upper,
  21.     thresholds->b.lower, thresholds->b.upper,
  22.     thresholds->c.lower, thresholds->c.upper);
  23. }
  24.  
  25. static void set_thresholds_0(struct threshold_t * const threshold,
  26.   const uint8_t lower, const uint8_t upper) {
  27.   threshold->lower = lower;
  28.   threshold->upper = upper;
  29. }
  30.  
  31. enum threshold {
  32.   THRESHOLD_A = offsetof(struct threshold_abc_t, a),
  33.   THRESHOLD_B = offsetof(struct threshold_abc_t, b),
  34.   THRESHOLD_C = offsetof(struct threshold_abc_t, c),
  35. };
  36.  
  37. static void set_thresholds_1(struct threshold_abc_t * const thresholds,
  38.   const enum threshold selection, const uint8_t lower, const uint8_t upper) {
  39.   struct threshold_t * const threshold =
  40.     (struct threshold_t * const)(&((uint8_t * const)thresholds)[selection]);
  41.   threshold->lower = lower;
  42.   threshold->upper = upper;
  43. }
  44.  
  45. int main() {
  46.   struct threshold_abc_t thresholds = {
  47.     .a = {
  48.       .lower = 5,
  49.       .upper = 15,
  50.     },
  51.     .b = {
  52.       .lower = 0,
  53.       .upper = 20,
  54.     },
  55.     .c = {
  56.       .lower = 0,
  57.       .upper = 30,
  58.     }
  59.   };
  60.   print(&thresholds);
  61.   set_thresholds_0(&thresholds.a, 2, 50);
  62.   print(&thresholds);
  63.   set_thresholds_1(&thresholds, THRESHOLD_C, 69, 99);
  64.   print(&thresholds);
  65.   return 0;
  66. }
Success #stdin #stdout 0s 1788KB
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{"a": {"lower": 5, "upper": 15},
 "b": {"lower": 0, "upper": 20},
 "c": {"lower": 0, "upper": 30}}
{"a": {"lower": 2, "upper": 50},
 "b": {"lower": 0, "upper": 20},
 "c": {"lower": 0, "upper": 30}}
{"a": {"lower": 2, "upper": 50},
 "b": {"lower": 0, "upper": 20},
 "c": {"lower": 69, "upper": 99}}
https://ideone.com/nJiyFG
language:
C (gcc 8.3)
created:
12 years ago
visibility:
public

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