c - 结构/union 初始化困惑

Question

我目前正在为下周一的考试做练习考试，我遇到了一些让我困惑的事情!

我有以下结构:

struct shape2d {
   float x;
   float y;
};

struct shape3d {
   struct shape2d base;
   float z;
};

struct shape {
   int dimensions;
   char *name;
   union {
      struct shape2d s1;
      struct shape3d s2;
   } description;
};

typedef struct shape Shape;

我必须创建一个函数来“创建”具有以下签名的形状:

Shape *createShape3D(float x, float y, float z, char *name);

因为我正在处理结构的 union ，所以我不太确定如何初始化我需要的所有字段!

这是我目前所拥有的:

Shape *createShape3D(float x, float y, float z, char *name) {
   Shape *s = (Shape *) malloc(sizeof(Shape));
   s->dimensions = 3;
   s->name = "Name..."; 

   // How can I initialize s2? 

   return s;
}

我们将不胜感激!

Answer 1

首先你需要将 name strcpy 到 s->name。

strcpy(s->name, "Name ...");

您可以将 s2 初始化为

s->description.s2.z = 0;
s->description.s2.base.x = 0;
s->description.s2.base.y = 0;

您可以在一本书中阅读更多关于 union 的内容。你也可以看这里

http://c-faq.com/struct/union.html

http://c-faq.com/struct/initunion.html

http://c-faq.com/struct/taggedunion.html