Initialization of structure with ternary operator

问题:

Why the ternary operator cannot be used to initialize a structure type, while it can be used to initialize a base type like int?

Example code :

#include <stdio.h>
#define ODD 1

int main(int argc, const char *argv[])
{
  static struct pair_str {
    int first; 
    int second; 
  } pair = ( ODD ) ?  {1,3} : {2,4}; // ERROR

  printf("pair %d %d\n", pair.first, pair.second); 

  int number = (ODD) ? 1 :2;  // FINE

  return 0;

}

Compiler errors :

/home/giuseppe/struct.c: In function ‘main’:
/home/giuseppe/struct.c:12:23: error: expected expression before ‘{’ token
/home/giuseppe/struct.c:12:29: error: expected expression before ‘:’ token

回答1:

Sure, use C99 compound literals:

pair = odd ? (struct pair_str){ 1, 3 } : (struct pair_str){ 2, 4 };