吴裕雄--天生自然C语言开发：共同体

union [union tag]
{
   member definition;
   member definition;
   ...
   member definition;
} [one or more union variables];

union Data
{
   int i;
   float f;
   char  str[];
} data;

#include <stdio.h>
#include <string.h>

union Data
{
   int i;
   float f;
   char  str[];
};

int main( )
{
   union Data data;        

   printf( "Memory size occupied by data : %d\n", sizeof(data));

   return ;
}

#include <stdio.h>
#include <string.h>

union Data
{
   int i;
   float f;
   char  str[];
};

int main( )
{
   union Data data;        

   data.i = ;
   data.f = 220.5;
   strcpy( data.str, "C Programming");

   printf( "data.i : %d\n", data.i);
   printf( "data.f : %f\n", data.f);
   printf( "data.str : %s\n", data.str);

   return ;
}

#include <stdio.h>
#include <string.h>

union Data
{
   int i;
   float f;
   char  str[];
};

int main( )
{
   union Data data;        

   data.i = ;
   printf( "data.i : %d\n", data.i);

   data.f = 220.5;
   printf( "data.f : %f\n", data.f);

   strcpy( data.str, "C Programming");
   printf( "data.str : %s\n", data.str);

   return ;
}