程序代码：

// union2.c--联合的典型用法

#include <stdio.h>

#define CHARACTER 'c'
#define INTEGER 'I'
#define FLOAT 'F'

struct generic_tag{
    char type;
    union shared_tag{
        char c;
        int i;
        float f;
        }shared;
};

void print_function(struct generic_tag generic);

int main(void)
{
    struct generic_tag var;
    
    var.type = CHARACTER;
    var.shared.c = '$';
    print_function(var);

    var.type = FLOAT;
    var.shared.f = (float) 12345.67890;
    print_function(var);

    var.type = 'x';
    var.shared.i = 111;
    print_function(var);
    return 0;
}

void print_function(struct generic_tag generic)
{
    printf("\n\nThe generic value is...");
    switch (generic.type)
    {
    case CHARACTER:    printf("%c", generic.shared.c);
    break;
    case INTEGER:    printf("%d", generic.shared.i);
    break;
    case FLOAT:    printf("%f", generic.shared.f);
    break;
    default:    printf("an unknown type: %c\n",
    generic.type);
    break;
    }
}