in example code generated by rpcgen (appname_server.c), there was union used as “define”. it was simmilar to this:

#include<stdlib.h>
#include<string.h>
#include<stdio.h>

#define alignof _Alignof
#define LOG(d) printf("> name: %5s, value: %8X, sizeof: %zu, alignof: %zun", #d, *(int*)&d, sizeof(d), alignof(d));

typedef int // or other type
  very_very_special_int_1,
  very_very_special_int_2;

int
main(int argc, char** argv)
{
  /**/// ======================

  // union --------------------
  union {
    very_very_special_int_1 very_very_special_int_1_variable; // descriptive/special name
  } foo; // new name, "define"

  memcpy(&foo, &(int){0xDEAD}, sizeof(int)); // some operations using new name, (passing by pointer)

  // struct --------------------
  struct {
    very_very_special_int_2 very_very_special_int_2_variable; // descriptive/special name
  } bar; // new name, "define"

  memcpy(&bar, &(int){0x7EC}, sizeof(int)); // some operations using new name, (passing by pointer)

  LOG( foo );
  LOG( bar );
  // */// ======================

  /* output --------------------
  > name:   foo, value:     DEAD, sizeof: 4, alignof: 4
  > name:   bar, value:      7EC, sizeof: 4, alignof: 4
  */

  return 0;
}

have you evered used it in your code? i dont see many advantages unless you are a code generator.