访问者模式--示例代码

#include<stdio.h>
#include<stdlib.h>
#include<string.h>
typedef struct{
   int state;
}JPG;
typedef struct{
   int state;
   int data;
}PNG;
typedef struct{
   int state;
}AVI;
JPG jpg;PNG png; AVI avi;
void vist_0(int s){
   printf("Frist vist! state:%d\n",jpg.state);
}
void vist_1(int s){
  printf("Sencond vist!state:%d\n",png.state);
}
void vist_2(int s){
    printf("Third vist!state:%d\n",avi.state);
}
void vistor(int v,int s){
    switch(v){
      case 0:vist_0(0);break;
      case 1:vist_1(1);break;
      case 2:vist_2(2);break;
    }
}
int main(){
  vistor(0,1);
  vistor(1,1);
  vistor(2,1);
  return 0;
}

typedef struct {
    void (*accept)(void (*visit)(void));
} Element;

void accept(Element* self, void (*visit)(void)) {
    visit();
}

void visitA() { printf("Visited A\n"); }
Element elementA = { .accept = accept };

// 使用
elementA.accept(&elementA, visitA); // 输出 "Visited A"