stackoverflow.com/questions/49711582

struct data_unit {
  enum {
    d_A, d_B, d_C
  } dtype;
  union {
    char * a;
    int * b;
    double * c;
  } data;
};

char * du_format_table = {"%c", "%d", "%lf"};

void print_data_unit(data_unit du){
    printf(format_table[du.dtype], du.data.a + du.dtype);
}