用C联盟的例子 [英] Examples of Union in C

问题描述

我在找一些工会的例子，而不是了解工会工作，我希望我做的，但是看到哪种黑客的人与工会做的。

I'm looking for some union examples, not to understand how union works, hopefully I do, but to see which kind of hack people do with union.

所以，随时分享你的工会破解（当然，:)一些解释）

So feel free to share your union hack (with some explanation of course :) )

推荐答案

一个典型就是要重新present未知类型的值，如一个简单的虚拟机的核心是：

One classic is to represent a value of "unknown" type, as in the core of a simplistic virtual machine:

typedef enum { INTEGER, STRING, REAL, POINTER } Type;

typedef struct
{
  Type type;
  union {
  int integer;
  char *string;
  float real;
  void *pointer;
  } x;
} Value;

使用这个你可以写code处理价值不知道他们的确切类型，例如实现堆栈等。

Using this you can write code that handles "values" without knowing their exact type, for instance implement a stack and so on.

由于这是（老，pre-C11）C，内部工会必须在外部给定的字段名称结构。在C ++中，你可以让联盟是匿名的。采摘这个名字能吃苦耐劳。我倾向于一些单字母，要因为它几乎从不单独引用，因此它总是从上下文中正在发生的事情不清楚。

Since this is in (old, pre-C11) C, the inner union must be given a field name in the outer struct. In C++ you can let the union be anonymous. Picking this name can be hard. I tend to go with something single-lettered, since it is almost never referenced in isolation and thus it is always clear from context what is going on.

code的值设置为一个整数，可能是这样的：

Code to set a value to an integer might look like this:

Value value_new_integer(int v)
{
  Value v;
  v.type = INTEGER;
  v.x.integer = v;
  return v;
}

下面我用一个事实，即结构 s时，可以直接返回，处理几乎像一个原始类型的值（可分配结构 S）。

Here I use the fact that structs can be returned directly, and treated almost like values of a primitive type (you can assign structs).

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