当我从 main 中拆分函数时，struct 出现问题

Question

I have a struct in my main let's say:

struct node
{
    char name[N];
    int num;
    char **group;
    int groupsize;
    struct node * next;
};

and I have my functions to other .c and .h files call myfuncs.ch

myfuncs.h

void create_node(struct node **, struct node **, int, int, char **, int);
void display(struct node *head);
void start_joseph(struct node **, int, int);

and myfuncs.c

void create_node(struct node **, struct node **, int, int, char **, int);
{
  do something;
}

void display(struct node *head);
{
  do something;
}

void start_joseph(struct node **, int, int);
{
  do something;
}

but I get this error

[Warning] 'struct node' declared inside parameter list
[Warning] its scope is only this definition or declaration, which is probably not what you want

Should I define the struct to the pre-processor or what?

Answer 1

Put the structure definition in the header before the function declarations that use it.

At minimum, you need a line:

struct node;

in the header before the function declarations. Since you don't appear to be trying to create an opaque type (the details of which would be hidden from the code using it), then embedding the entire structure definition is reasonable. Note that you then delete that definition from the code holding the main() function.

What the error message says is that if you write:

void create_node(struct node **, struct node **, int, int, char **, int);

and there is no previous mention of the type struct node , then the type name is created but only exists for that one function declaration. The next function that refers to struct node creates a new type name struct node which is different from and incompatible with the previous one. By declaring struct node; at file scope, you're saying "there is a type struct node ". Basically, you have to have something outside the scope of a prototype that says "there is a type struct node " which the function prototype can then use.

Suggested solution — myfuncs.h :

#ifndef MYFUNCS_H_INCLUDED
#define MYFUNCS_H_INCLUDED

struct node
{
    char name[N];
    int num;
    char **group;
    int groupsize;
    struct node * next;
};

extern void create_node(struct node **, struct node **, int, int, char **, int);
extern void display(struct node *head);
extern void start_joseph(struct node **, int, int);

#endif /* MYFUNCS_H_INCLUDED */

The header guards prevent problems if the file is included multiple times in a single translation unit (source file plus included headers). I use extern on function declarations to match the extern needed on variables declared in the header; many people don't. That choice is up to you and/or the coding guidelines you work with. Removing the extern makes no difference to the result.

Answer 2

I think you should declare node struct at other header file, eg global.h, and include the global.h in myfuncs.h.

  // in the global.h 
 struct node
 {
      char name[N];
      int num;
      char **group;
      int groupsize;
      struct node * next;
  };
  ....    ....
 // in the myfuncs.h
 #include "global.h"

Answer 3

In these function declarations

void create_node(struct node **, struct node **, int, int, char **, int);
void display(struct node *head);
void start_joseph(struct node **, int, int);

the type struct node has the function prototype scopes of each function declaration and is not visible outside the parameter declaration lists.

The same problem exist with the function definitions. And the warnings

[Warning] 'struct node' declared inside parameter list
[Warning] its scope is only this definition or declaration, which is probably not what you want

point to this.

The declaration of the structure in main has the function main block scope and is also invisible outside the function.

You need at least declare (or define) the structure before the function declarations and the structure shall be already defined before the function definitions.

So move the structure definition from main to a point before the function declarations.

For example

myfuncs.h

struct node
{
    char name[N];
    int num;
    char **group;
    int groupsize;
    struct node * next;
};

void create_node(struct node **, struct node **, int, int, char **, int);
void display(struct node *head);
void start_joseph(struct node **, int, int);