union.c

#include <stdio.h>

struct vec4_a {
  union { float x, r; } a;
  union { float y, g; } b;
  union { float z, b; } c;
  union { float w, a; } d;
};

union vec4_b {
  struct {
    float x, y, z, w;
  } axis;
  struct {
    float r, g, b, a;
  } color;
  float data[4];
};

struct vec4_c {
  union {
    struct {
      float x, y, z, w;
    } axis_;
    struct {
      float r, g, b, a;
    } color_;
  } vec3;
};

int main(int argc, char *argv[]) {
  struct vec4_a a = {{1}, {2}, {3}, {4}};
  union vec4_b b = {{1, 2, 3, 4}};
  struct vec4_c c = {{{1, 2, 3, 4}}};
  printf("%zu\n", sizeof (struct vec4_a));
  printf("%zu\n", sizeof (union vec4_b));
  printf("%zu\n", sizeof (struct vec4_c));
  return 0;
}