指针在C自我结构 [英] Pointer to self struct in C

问题描述

由于以下code：

typedef struct elementT {
  int data;
  struct elementT *next;
} element;

为什么有必要做结构elementT *下一，我不能做元素*下一里面的结构声明本身？是不是因为它是尚未宣布？

Why is it necessary to do struct elementT *next and I can't do element *next inside the struct declaration itself? Is it because it is not declared yet?

推荐答案

的的typedef 只发生后，结构已被定义。请看下面的code;语法是无效的，但它希望它显示订单/ $ P $的东西pcedence：

The typedef only takes place after the struct has been defined. Consider the following code; the syntax is invalid, but it hopes it shows the order/precedence of things:

typedef (struct {
  int field1, field2;
}) item;

即，在结构{...} 是一个前pression，它表示一个类型。通过给它一个名称的该类型的typedef 工作

I.e., the struct{...} is an "expression" that denotes a type. The typedef operates on that type by giving it a name.

相反，

struct foo {
    foo *next;
};

工程的C因为两个特殊的规则：结构＆LT;名称＆gt; 不仅定义了一个类型，但给它一个结构标记为好，而标签是结构声明的其余部分（原因很明显内立即可见：链表，树等，将是非常痛苦没有这些规则来实现）。

works because of two special rules of C: struct <name> not only defines a type, but gives it a struct tag as well, and that tag is immediately visible inside the rest of the struct declaration (for the obvious reason: linked lists, trees, etc. would be very painful to implement without these rules).

这篇关于指针在C自我结构的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！