Union

A Union is like a structure, except that each
element shares the same memory. Thus in this
example, the coords and about members overlap.

Note that the setting of about[2] to 'X' CORRUPTS
the float in this demonstration.

In a practical use, a variable such as un_type
(provided but not used in this example) would be
set up to indicate which particular use is being
made of the union

*/
typedef union {
float coords[3];
char about[20];
} assocdata;

typedef struct {
char *descript;
int un_type;
assocdata alsostuff;
} leaf;

int main() {
leaf oak[3];
int i;

printf ("Hello World\n");

for (i=0; i<3; i++) {
oak[i].descript = "A Greeting";
oak[i].un_type = 1;
oak[i].alsostuff.coords[0] = 3.14;
}
oak[2].alsostuff.about[2] = 'X';

for (i=0; i<3; i++) {
printf("%s\n",oak[i].descript);
printf("%5.2f\n",oak[i].alsostuff.coords[0]);
}

}

/* Sample of output from this program

[trainee@daisy cd07]$ ./union
Hello World
A Greeting
3.14
A Greeting
3.14
A Greeting
3.39
[trainee@daisy cd07]$