面向对象的C:构建vtable(Object oriented C: Building vtables)
我正在尝试自学基于面向对象的C语言。我正在尝试构建vtables,然后使用它们来模拟结构的“继承”(尝试在C ++中复制类继承)。
我有一个问题..我相信这是可能的,但我不知道该怎么做。 可以从“base”结构的指针修改“派生”结构的变量吗?
#include <stdio.h> #include <stdlib.h> //should represent Base typedef struct Animal { int age; void *vtable; } Animal; //Cat and dog will inherit Animal. They both have same 'age' variable, and different other parameters typedef struct Dog { int age; double weight; void *vtable; } Dog; typedef struct Cat { int age; int numberOfLives; void *vtable; } Cat; //some test functions void Speak_Dog(Animal* a) { printf("Woof!\n"); } void Speak_Cat(Animal* a) { printf("Meow!\n"); } //this is where I'm stuck, I would like to keep sending pointer to Animal double Dog_GetCost(Animal *a) { return 0;//should return age*weight } double Cat_GetCost(Animal *a) { return 0; //should return age*num_lives } //build tables void* Dog_Vtable[2] = {Speak_Dog, Dog_GetCost}; void* Cat_Vtable[2] = {Speak_Cat, Cat_GetCost}; void Construct_Dog(Dog* d) { d->age = 0; d->weight = 0; d->vtable = Dog_Vtable; } void Construct_Cat(Cat* c) { c->age = 0; c->numberOfLives = 0; c->vtable = Cat_Vtable; } int main() { int choice; Dog d; Cat c; Animal* a; ((void (*)(Animal*))Dog_Vtable[0])((Animal*)&d); //print out "woof" - good ((void (*)(Animal*))Cat_Vtable[0])((Animal*)&c); //print out "meow" - good printf("Do you want to make dog or a cat? (0/1) "); scanf("%d", &choice); if(choice == 0) { a = &d; //animal is Dog a = (Animal*)malloc(sizeof(Dog)); //allocate memory for Dog Construct_Dog(a); //construct it } else { a = &c; //similar for cat a = (Animal*)malloc(sizeof(Cat)); Construct_Cat(a); } free(a); return 0; }
现在,假设我尝试修改第二个int变量(weight或NumLives,取决于),我将如何使用
*a
更改它? 我正在尝试学习Object oriented programming with ANSI-C
,但我没有想到这一点。I'm trying to teach myself basics of object oriented C. I'm trying to build vtables and then use those to simulate "inheritance" of structs (try to copy class inheritance in C++).
I have a question.. I believe it is possible, but I don't know how to do it. Can variable of "derived" struct be modified from pointer of "base" struct?
#include <stdio.h> #include <stdlib.h> //should represent Base typedef struct Animal { int age; void *vtable; } Animal; //Cat and dog will inherit Animal. They both have same 'age' variable, and different other parameters typedef struct Dog { int age; double weight; void *vtable; } Dog; typedef struct Cat { int age; int numberOfLives; void *vtable; } Cat; //some test functions void Speak_Dog(Animal* a) { printf("Woof!\n"); } void Speak_Cat(Animal* a) { printf("Meow!\n"); } //this is where I'm stuck, I would like to keep sending pointer to Animal double Dog_GetCost(Animal *a) { return 0;//should return age*weight } double Cat_GetCost(Animal *a) { return 0; //should return age*num_lives } //build tables void* Dog_Vtable[2] = {Speak_Dog, Dog_GetCost}; void* Cat_Vtable[2] = {Speak_Cat, Cat_GetCost}; void Construct_Dog(Dog* d) { d->age = 0; d->weight = 0; d->vtable = Dog_Vtable; } void Construct_Cat(Cat* c) { c->age = 0; c->numberOfLives = 0; c->vtable = Cat_Vtable; } int main() { int choice; Dog d; Cat c; Animal* a; ((void (*)(Animal*))Dog_Vtable[0])((Animal*)&d); //print out "woof" - good ((void (*)(Animal*))Cat_Vtable[0])((Animal*)&c); //print out "meow" - good printf("Do you want to make dog or a cat? (0/1) "); scanf("%d", &choice); if(choice == 0) { a = &d; //animal is Dog a = (Animal*)malloc(sizeof(Dog)); //allocate memory for Dog Construct_Dog(a); //construct it } else { a = &c; //similar for cat a = (Animal*)malloc(sizeof(Cat)); Construct_Cat(a); } free(a); return 0; }
Now, let's say I try to modify 2nd int variable (weight or NumLives, depending), how would I change it using
*a
? I'm trying to learn fromObject oriented programming with ANSI-C
, but I fail to figure this out.
原文:https://stackoverflow.com/questions/36611591
最满意答案
FAB始终在UI上设计 :
浮动操作按钮用于特殊类型的提升操作。 它们通过浮动在UI上方的带圆圈的图标来区分,并且具有与变形,发射和传递锚点相关的特殊运动行为。
我还没有检查它是如何实现的,所以除非有其他人得到更好的答案,你可以查看
CoordinatorLayout
和FAB来源,看看是什么让它在UI上徘徊,或者如果时间很短,你只需要放一些看起来像FAB的东西(或者你使用常规按钮和适当的drawable,或第三方lib)。FAB is always over UI by design:
Floating action buttons are used for a special type of promoted action. They are distinguished by a circled icon floating above the UI and have special motion behaviors related to morphing, launching, and the transferring anchor point.
I haven't checked how it is implemented so unless someone else come with better answer you can either check
CoordinatorLayout
and FAB sources to see what makes it hoovering over UI, or if time is short you simply put something that looks like FAB (either you use regular button with proper drawable, or 3rd party lib).
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