C和指针之联合体大小

1、联合体的特点和大小

union是共用一个内存首地址，联合体中每个成员的地址都相同,等于联合体变量的首地址
联合体的大小足够容纳最宽的成员,大小能被其包含的所有基本数据类型的大小所整除

2、测试Demo

  

   

    

     

    
    

     

      #include <stdio.h>
     
    
   

    

     

    
    

     
 
     
    
   

    

     

    
    

     

      union var 
     
    
   

    

     

    
    

     

      {
     
    
   

    

     

    
    

     

      	long int a;
     
    
   

    

     

    
    

     

      	int b;
     
    
   

    

     

    
    

     

      };
     
    
   

    

     

    
    

     
 
     
    
   

    

     

    
    

     
 
     
    
   

    

     

    
    

     

      union size
     
    
   

    

     

    
    

     

      {
     
    
   

    

     

    
    

     

      	int a;
     
    
   

    

     

    
    

     

      	double b;
     
    
   

    

     

    
    

     

      	char c[11];
     
    
   

    

     

    
    

     

      };
     
    
   

    

     

    
    

     
 
     
    
   

    

     

    
    

     

      int main()
     
    
   

    

     

    
    

     

      {
     
    
   

    

     

    
    

     

      	union var v;
     
    
   

    

     

    
    

     

      	v.a =  3.14;
     
    
   

    

     

    
    

     

      	printf("v.b is %d\n", v.b);
     
    
   

    

     

    
    

     

      	v.b = 6;
     
    
   

    

     

    
    

     

      	printf("v.a is %ld the address is %p\n", v.a, &v.a);
     
    
   

    

     

    
    

     

      	printf("v.b is %d the address is %p\n", v.b, &v.b);
     
    
   

    

     

    
    

     
 
     
    
   

    

     

    
    

     

      	union size union_first;
     
    
   

    

     

    
    

     

      	union size union_second;
     
    
   

    

     

    
    

     

      	union size union_third;
     
    
   

    

     

    
    

     
 
     
    
   

    

     

    
    

     

      	//大小足够容纳最宽的成员,大小能被其包含的所有基本数据类型的大小所整除
     
    
   

    

     

    
    

     

      	printf("the sizeof union_first is %d\n", sizeof(union_first));
     
    
   

    

     

    
    

     

      	printf("the sizeof union_second is %d\n", sizeof(union_second));
     
    
   

    

     

    
    

     

      	printf("the sizeof union_third is %d\n", sizeof(union_third));
     
    
   

    

     

    
    

     

      	printf("sizeof(long int) is %d\n", sizeof(long int));
     
    
   

    

     

    
    

     

      	printf("the sizeof
     
    
  
 

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原文链接：chenyu.blog.csdn.net/article/details/78650139