typedef结构指针定义 [英] typedef struct pointer definition

问题描述

我是C语言的新手，所有指针内容都有一些问题.

I'm pretty new in C and having some problems with all the pointer stuff.

我写了这段代码:

typedef struct edgeitem
{
    double          weight;
}EDGE_ITEM, *pEDGE_ITEM; //also declaration of a pointer

/************ edge that includes a pointer to the edge item, next and prev ******/
typedef struct edge
{
    pEDGE_ITEM  *edge_item;  
    pEDGE       *next;      //pointer to next edge
    pEDGE       *prev;      //pointer to prev edge
}EDGE, *pEDGE;

这样我会出错，只是不明白为什么.

I get an error this way and just cant understand why.

我知道edgeitem和edge是标签，可以使用struct edge *next，但是我声明了指针，所以我怎么不能使用它们呢?

I know that edgeitem and edge are tags and I can use struct edge *next but I declared the pointers so how come i can't use them?

如果我有指针，我需要使用*吗?

Do i need to use * if I have a pointer?

pEDGE_ITEM *edge_item
//or
pEDGE_ITEM edge_item

我不明白，它是一个指针，所以为什么要添加*?

I cant understand, it's a pointer so why do I add the *?

最后一个问题是: 如果我使用上面的方法，两者之间有什么区别?

And the last question is: If I'm using the above, what's the difference between:

*EDGE  next
EDGE  *next

最后一个: 如果我要添加:

and last one : if I'm adding:

typedef struct edge_list
{
    EDGE        *head;
}EDGE_LIST;

与:

pEDGE      head;

推荐答案

您不能在结构定义中使用pEDGE.您应该执行以下操作:

You cannot use pEDGE within the definition of the struct. You shoud do something like:

typedef struct edge {
    pEDGE_ITEM          *edge_item;  
    struct edge         *next;      //pointer to next edge
    struct edge         *prev;      //pointer to prev edge
} EDGE, *pEDGE;

您还必须注意，edge_item是双指针.您在问题中也提到了这一点.因此，如果您使用pEDGE_ITEM并且只想拥有一个普通的指针，则不应该编写pEDGE_ITEM *edge_item，而只需编写pEDGE_ITEM edge_item.

You must also note that edge_item is a double pointer. You also mention that in your question. So if you use pEDGE_ITEM and you just want to have a normal pointer you should not write pEDGE_ITEM *edge_item but just pEDGE_ITEM edge_item.

为澄清起见，以下所有声明都是等效的:

For clarifying, all the following declarations are equivalent:

struct edgeitem *edge_item;
EDGE_ITEM *edge_item;
pEDGE_ITEM edge_item;

但是

pEDGE_ITEM *edge_item;

等同于

struct edgeitem **edge_item;
EDGE_ITEM **edge_item;

关于*EDGE next的语法错误.正确的语法为EDGE* next或pEDGE next.因此，一旦定义了struct edge，您就可以使用这两个中的任何一个，但是在定义结构时，您必须按照我在答案开头所显示的那样进行操作.

About *EDGE next that is wrong syntax. The correct syntax would be EDGE* next or pEDGE next. So once struct edge is defined you can just use any of these two, but while defining the struct, you must do as I show at the beginning of my answer.

是的，以下两个定义是等效的:

Yes, the following two definitions are equivalent:

typedef struct edge_list {
    EDGE        *head;
} EDGE_LIST;

typedef struct edge_list {
    pEDGE        head;
} EDGE_LIST;

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