使用struct和typedef的编译器错误

Question

I have the following files in my VS project:

// list.h

#include "node.h"

typedef struct list list_t;

void push_back(list_t* list_ptr, void* item);

// node.h

typedef struct node node_t;

// node.c

#include "node.h"

struct node
{
   node_t* next;
};

// list.c

#include "list.h"


struct list
{
    node_t* head;
};

void push_back(list_t* list_ptr, void* item)
{
   if(!list_ptr)
       return;

   node_t* node_ptr; // Here I have two compiler errors
}

I have the compiler errors: Compiler Error C2275 and Compiler Error C2065 .

Why? How can i fix this problem?

Answer 1

Here's what list.h looks like after the pre-processor handles the #include lines (some comments excluded):

// list.h 

typedef struct node node_t;

typedef struct list list_t; 

void push_back(list_t* list_ptr, void* item); 

When you use this header inside list.c, the compiler has problems with struct node because it is not defined in this context. It is only defined in node.c, but the compiler can't see that definition from list.c.

Since you're only using pointers to node_t , try changing node.h to look like this:

// node.h     

struct node;
typedef struct node node_t;

Now, you've pre-declared that there is a data type called struct node . It's enough information for the compiler to handle typedef s and create pointers, but since it hasn't been completely defined you can't declare an object of type struct node or de-reference a struct node pointer.