示例代碼:
/* how to simulate C++'s polymorphism with C */
#include<stdio.h>
#include<stdlib.h>
#include<string.h>
/* declaration of virtual method */
typedef void (*Func1)(void);
typedef void (*Func2)(int);
typedef void (*Func3)(char *);
/* ------------------- Base Class begin ------------------*/
void func1_base(void)
{
printf("func1_base(void) called\n");
}
void func2_base(int item)
{
printf("func2_base(%d) called\n", item);
}
struct Vtbl_Base {
Func1 f1;
Func2 f2;
};
struct Vtbl_Base bvtbl = {&func1_base, &func2_base};
struct Base {
void *vptr; /* pointer to VTABLE */
int field_base;
};
void Base_Init(struct Base *base, int value)
{
base->vptr = &bvtbl;
base->field_base = value;
}
/* ------------------- Base Class end ------------------*/
/* ------------------- Derived Class begin ------------------*/
void func1_derived(void)
{
printf("func1_derived(void) called\n");
}
void func3_derived(char *item)
{
printf("func3_derived(%s) called\n", item);
}
struct Vtbl_Derived {
struct Vtbl_Base vtbl_base;
Func3 f3;
};
struct Vtbl_Derived dvtbl = {{&func1_derived, &func2_base}, &func3_derived};
struct Derived {
struct Base base;
int field_derived;
};
void Derived_Init(struct Derived *derived, int b, int d)
{
Base_Init((struct Base *)derived, b);
derived->base.vptr = &dvtbl;
derived->field_derived = d;
}
/* ------------------- Derived Class end ------------------*/
void
test_polymorphism(struct Base *obj)
{
((struct Vtbl_Base *)(obj->vptr))->f1();
((struct Vtbl_Base *)(obj->vptr))->f2(obj->field_base);
}
int
main(int argc, char **argv)
{
struct Base base;
Base_Init(&base, 128);
test_polymorphism(&base);
struct Derived derived;
Derived_Init(&derived, 128, 256);
test_polymorphism((struct Base *)&derived);
((struct Vtbl_Derived *)(*(int *)&derived))->f3("polymorphism");
}