如果 ptr 是指针，那么 typedef ptr p 和 typedef struct ptr p 有什么区别？

Question

update: thanx for your help!It's my mistake. I see the code from"Data structures and Algorithm Analysis:in c" but I misunderstood it, I tried and the code reported errors,so maybe I am not using it correctly. Maybe the code is just sth like Exmaple. I found the code in later pages and it is what I thought to be.The problem is solved.

-----------original question: what's the difference between:

typedef struct node *ptr;
typedef struct ptr tree;

and:

typedef ptr tree?

we can use the second one to create a list, can we define a B-tree in this way?

if not, what's the difference? (thanks)

Answer 1

First of all you don't really have to write the word struct if node is already defined, so the following is fine:

struct node
{
};

typedef node *nptr; //same result as typedef struct node *nptr;

nptr nodePointer = new node();

However, you can use the typedef struct syntax as follows:

typedef struct {int first; int second;} S, *sPtr;
sPtr pointerToS; //same as S * pointerToS

Now, in your example you have

typedef struct node *ptr;
typedef struct ptr tree;

The first line means that ptr now means a pointer to node . The second line basically says "please call the ptr structure a tree from now on". However, ptr is a pointer to node , not a struct , that's why you will get an error similar to using typedef-name 'ptr' after 'struct' .

The line

typedef ptr tree;

on the other hand, says "please call ptr a tree from now on", no matter what ptr is, so it compiles fine.