原型

//Prototype: a pointer to a function plays the virtual clone()
typedef struct Shape {
    const char *color;
    struct Shape *(*clone)(const struct Shape *self);
} Shape;

//ConcretePrototype: the base struct is the first field
typedef struct {
    Shape base;
} Square;

//only the concrete type knows its size, so it makes the copy;
//assigning a struct copies all its fields
Shape *squareClone(const Shape *self) {
    Square *copy = malloc(sizeof *copy);
    *copy = *(const Square *)self;
    return &copy->base;
}

//Client
typedef struct {
    const Shape *shape;
} ShapeMaker;

Shape *makeShape(const ShapeMaker *maker) {
    return maker->shape->clone(maker->shape);
}

Square square = {{"Red", squareClone}};
ShapeMaker maker = {&square.base};

Shape *square1 = makeShape(&maker);
Square *square2 = (Square *)makeShape(&maker);
//square1->color is "Red"
//square2->base.color is "Red"
bool same = square1 == &square2->base;
//same is false: each call makes a new copy

printf("color1 is %s\n", square1->color);
printf("color2 is %s\n", square2->base.color);
printf("same is %s\n", same ? "true" : "false");
free(square1);
free(square2);