Today, a friend of mine asked me to show him an example of how one can create a function in C that accepts an argument of different specified types. This example is what I came up with in about 3 minutes while on the phone with him (so it most likely can be better). Needless to say, I used a `union` in order to provide this functionality. Due to…

union-example.c

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

#define INT_OR_STR_INT 1
#define INT_OR_STR_STR 2

typedef struct
{
    unsigned int type;
    union
    {
        unsigned int integer;
        // I think I can safely assume that no one is older than 999.
        char string[ 4 ];
    } value;
} int_or_str;

void print_age( int_or_str age );

int main()
{
    int_or_str age_1;
    int_or_str age_2;

    age_1.type          = INT_OR_STR_INT;
    age_1.value.integer = 18;

    print_age( age_1 );

    age_2.type = INT_OR_STR_STR;

    strcpy( age_2.value.string, "18" );

    print_age( age_2 );

    return 0;
}

void print_age( int_or_str age )
{
    switch ( age.type )
    {
        case INT_OR_STR_INT:
            printf( "Age: %u.\n", age.value.integer );

            break;
        case INT_OR_STR_STR:
            printf( "Age: %s.\n", age.value.string );

            break;
    }
}