Question

I have main in which I used the node struct however defintion of node and it’s manipulation operations are localed in a file in the directory called NODE/

I created NODE/node.h which has:

typedef struct node node;

struct node
{
        int my_reg;
        node *left;
        node *right;
} ;

I created NODE/node.c and include in it node.h which has node_insert node_remove;

However I am using the node struction in school_address.c in which I also include NODE/node.h and NODE/node.c

I tried putting

extern struct node

in school_address.c

Yet the code doesn’t compile and complains of redefinition in node.h

Any idea?

Answer 1

extern is for variables, not type definitions. You should just include the header in all modules that need to know about struct node; that is substituted for the entire header’s content, inline.

What you should not do is include a C file in another C file. Instead, you should declare the prototypes of the common functions in a header.

E.g.,

#include "node.h"

int main()
{
    // whatever
}

becomes, if you put the prototype for node_insert in the header,

typedef struct node node;

struct node
{
        int my_reg;
        node *left;
        node *right;
};

struct node *node_insert(struct node *, int);  // or whatever the prototype is

int main()
{
    // whatever
}

after the C preprocessor is done with it, so struct node and node_insert are visible in main.