c语言中结构体指针的强制类型转换

enum kind {E_INT, E_ADD, E_TIMES};

struct Exp {
  enum Exp_Kind_tkind;    
}

struct Exp_Add{
  enum Exp_Kind_tkind;
　struct Exp *left;
　struct Exp *right;
}

 https://blog.csdn.net/flyqwang/article/details/6420228