C语言 联合(union)用法案例详解

#include "stdio.h"
union{
    int a;
    float b;  
    char c;
}x;
int main()    
{  
    x.c='x';
    x.b=3.14;
    x.a=25;
    printf("%g \t%c \t %d\t\n",x.b,x.c,x.a);
    return 0;          
}

#include<stdio.h>  
union var{  
        long int l;  
        int i;  
};  
main(){  
        union var v;  
        v.l = 5;  
        printf("v.l is %d\n",v.i);  
        v.i = 6;  
        printf("now v.l is %ld! the address is %p\n",v.l,&v.l);  
        printf("now v.i is %d! the address is %p\n",v.i,&v.i);  
}  
//结果：  
//v.l is 5  
//now v.l is 6! the address is 0xbfad1e2c  
//now v.i is 6! the address is 0xbfad1e2c  

#include<stdio.h>  
union u{  
    int i;  
    double d;//这个union有8字节大小  
};  
main(){  
    union u uu;  
    uu.i = 10;  
    printf("%d\n",uu.i);  
    char * c;  
    c = (char *)&uu;//把union的首地址赋值、强转成char类型  
    c[0] = 'a';  
    c[1] = 'b';  
    c[2] = 'c';  
    c[3] = '\0';  
    c[4] = 'd';  
    c[5] = 'e';  
    //最多能到c[7]  
    printf("%s\n",c);//利用结束符'\0'打印字符串"abc"  
    printf("%c %c %c %c %c %c\n",c[0],c[1],c[2],c[3],c[4],c[5]);  
}  

 printf("%s\n",c);//利用结束符'\0'打印字符串"abc" 字符串以‘\0'结束所以后面未打印

main()
{
   struct
   {
      char name[10];
      int age;
      char job;
      union
      {
         int class;
         char office[10];
      } depa;
   }body[2];
   
　　int n,i;
   for(i=0;i<2;i++)
   {
      printf("input name,age,job and department\n");
      scanf("%s %d %c",body[i].name,&body[i].age,&body[i].job);
      if(body[i].job=='s')
         scanf("%d",&body[i].depa.class);
      else
         scanf("%s",body[i].depa.office);
   }
   printf("name\tage job class/office\n");
   for(i=0;i<2;i++)
   {
   if(body[i].job=='s')
      printf("%s\t%3D %3c %d\n",body[i].name,body[i].age ,body[i].job,body[i].depa.class);
   else
      printf("%s\t%3d %3c %s\n",body[i].name,body[i].age, body[i].job,body[i].depa.office);
   }
}