C语言实现虚函数机制¶
实现方式¶
- 虚函数指针
- 虚表
- 执行函数
代码实现¶
c_virtual_function.c
#include <stdio.h>
struct Animal {
const struct AnimalClass* class; //virtual ptr
};
struct AnimalClass {
void (*Eat)(struct Animal*); //virtual function
}; //virtual table
// normal function
void Move(struct Animal* self) {
printf("This is nomal move: %p\n", (void*)self);
}
// virtual function
void Eat(struct Animal* self) {
const struct AnimalClass* c = *(const void**)self;
if(c->Eat) {
c->Eat(self);
}else{
fprintf(stderr, "Eat not implement.\n");
}
}
//function in virtual function
static void real_eat(struct Animal* self) {
printf("This is real eat funtion: %p\n", (void*)self);
}
const struct AnimalClass Animal = {(void*)0}; //一个虚表为空：无多态
const struct AnimalClass RealEat = {real_eat}; //另一个虚表存放真正的执行函数：有多态
int main() {
struct Animal animal = {&Animal}; //一个对象中无虚函数指针
struct Animal realEat = {&RealEat}; //另一个对象有虚函数指针
Move(&animal);
Move(&realEat);
// 虚函数执行各自真正的执行函数
Eat(&animal);
Eat(&realEat);
return 0;
}
在Dev C++ 中使用C99，编译结果如下：