Question

Suppose I have a file insert.c in which two functions are defined:
1.insert_after
2.insert_before

The definitions of these func are something like this:

insert_after(arg1)
{ 
  if(condition 1)
    { ......... } 
  else
    insert_before(arg1); 
}

insert_before(arg)
{ 
  if(condition 1)
    { ......... } 
  else
    insert_after(arg); 
}
    

Now if this file insert.c is included in main.c and insert_after function is called

# include "insert.c"
int main()
{
  insert_after(arg);
  return 0;
}

On compiling main.c using gcc,the following error is encountered:

conflicting types for ‘insert_before’

note: previous implicit declaration of ‘insert_before’ was here

What is wrong here and how to avoid it?

Answer 1

This is because you don’t declare prototypes for your functions. A function which has no prototype, by default, has an unknown set of arguments and returns an int. But this is not the case for insert_before.

Create a file insert.h in which you declare them:

#ifndef INSERT_H
#define INSERT_H

void insert_before(type_of_arg);
void insert_after(type_of_arg);

#endif /* INSERT_H */

and include this file at the top of insert.c.

You should then compile with:

gcc -Wall -Wstrict-prototypes -Wmissing-prototypes -o progname insert.c main.c