um exemplo de polimorfismo em C!

test_polymorph.c

#include <stdio.h>

typedef struct polymorph polymorph;
struct polymorph
{
    void* data;
    int (*compare) (polymorph*, void*);
};

int polymorph_compare(polymorph* p1, polymorph* p2)
{
    return p1->compare(p1, p2->data);
}

int compare_default(polymorph* p, void* data)
{
    if (p->data < data)
    {
        return -1;
    }
    else if (p->data > data)
    {
        return 1;
    }
    else
    {
        return 0;
    }
}

int main(int argc, char* argv[])
{
    if (argc != 3)
    {
        printf("Usage: %s value1 value2\n", argv[0]);
        return 0;
    }
    polymorph p1 = { (void*) atoi(argv[1]), &compare_default };
    polymorph p2 = { (void*) atoi(argv[2]), &compare_default };

    printf("p1 = %d\np2 = %d\n", (int) p1.data, (int) p2.data);
    int r = polymorph_compare(&p1, &p2);
    printf("p1 %s p2\n", ((r < 0) ? "<" : ((r > 0) ? ">" : "==")));

    return 0;
}