how to passing cofunc as parameter to another function

 Anyone can help me, I get error when passing cofunc as parameter to another function. My code as follows:

cofunc char *getMonth(int num){
   static char *const months[12] = {"January", "February", "March", "April", "May", "June", "July", "August", "September", "October", "November", "December"};
   if(num>=1 && num<=12) return months[num-1];
}

void main() {
   char buffer[15];

   costate {
       memset(buffer, '\0', sizeof(buffer));
       memcpy(buffer, wfd getMonth(1), sizeof(buffer)); // error in here
       printf("Month: %s", buffer);
   }
}