在 C++ 中访问联合内的结构时出现问题

Question

   union hello
   {
      struct hi
      {
         uint8_t trees;
         uint8_t plants[6];
      };
      uint8_t forest[1 + 6];
   };

   struct world
   {
      hello a;
   };

typedef std::vector<world> universe;
universe alpha;

if I want to access the structure hi inside hello, then I am doing something like, assuming accessing the 1st vector element

alpha.at(1).a.hi.trees = 1; // error in accessing "hi" , why can't I access hi like this?  

ERROR: type name is not allowed

Answer 1

the struct is not a field of union in your version; it's just nested type name. change it to this:

   union hello
   {
      struct
      {
         uint8_t trees;
         uint8_t plants[6];
      } hi;/*<< put the field name here*/
      uint8_t forest[1 + 6];
   };