container.c

#include <stdio.h>
#include <stdlib.h>

typedef enum type
{
    CHAR,
    INT,
    LONG
} type;

typedef struct container
{
    type t;
    void *val;
} container;

typedef union types
{
    char c;
    int i;
    long l;
} types;

void printChar(container *c);

int main(int argc, char *argv[]) 
{
    container *cont = malloc(sizeof(struct container));
    types *t = malloc(sizeof(union types));
	
    // Set the container to hold a char 'a'
    t->c = 'a';
    cont->t = CHAR;
    cont->val = t;

    printChar(cont);

    free (t);
    free(cont);
}

void printChar(container *cont)
{
    if (cont->t != CHAR)
    {
        printf("Not a char!");
        return;
    }

    char c = *((char *)(cont->val));
    printf("Char: %c", c);
}