Created
June 1, 2017 12:10
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a simple virtual-table implemented polymorphism simulation in C
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#include <stdio.h> | |
#include <stdlib.h> | |
struct Base; | |
struct Derived; | |
int f_Base(struct Base * b); | |
int f_Derived(struct Derived* d); | |
typedef struct { | |
int (*f)(struct Base *); | |
} VTable_Base; | |
VTable_Base vtable_base; | |
VTable_Base vtable_derived; | |
int vptr_init() { | |
vtable_base.f = f_Base; | |
//warning: incompatible pointer types assigning to 'int (*)(struct Base *)' from 'int (struct Derived *)' | |
vtable_derived.f = f_Derived; | |
return 0; | |
} | |
struct Base { | |
VTable_Base* vptr; | |
int i; | |
}; | |
struct Derived { | |
VTable_Base* vptr; | |
struct Base b; | |
int j; | |
}; | |
int f_Base(struct Base * b) { | |
printf("base::f, i = %d\n", b->i); | |
return b->i; | |
} | |
int f_Derived(struct Derived* d) { | |
printf("derived::f, i = %d\n", d->b.i); | |
return d->b.i; | |
} | |
int f(struct Base * b) { | |
return b->vptr->f(b); | |
} | |
struct Base* make_Base() { | |
struct Base * b = malloc(sizeof(struct Base)); | |
b->vptr = &vtable_base; | |
return b; | |
} | |
struct Derived* make_Derived() { | |
struct Derived * d = malloc(sizeof(struct Derived)); | |
d->vptr = &vtable_derived; | |
return d; | |
} | |
int main() { | |
vptr_init(); | |
struct Derived *d = make_Derived(); | |
d->b.i = 10; | |
f((struct Base *)d); //derived::f, i = 10 | |
free(d); | |
struct Base *b = make_Base(); | |
b->i = 15; | |
f(b); //base::f, i = 15 | |
free(b); | |
} |
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