gcc warning: function used but not defined

Question

I am getting the warning: function used but not defined. I have static __inline__ in header file say a.h. The header file is included in <

Answer 1

Declare the function normally in the header file

a.h

#ifndef A_H_INCLUDED
#define A_H_INCLUDED

void function1(void);

#endif

Define the function in a single code file with no static

a.c

#include "a.h"

void function1(void) {
  /* function definition */
}

and call the function from other files, after including the header

b.c

#include "a.h"

void quux(void) {
  function1(); /* call regular function */
}

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The way you had before (static and implementation in header file) worked because each code file that included that header got its own version of the function; different to every other function of the same name in every other file (but doing exactly the same).