How to declare function pointer in header and c-file?

Question

I\'m a little confused over how to declare a function pointer in a header file. I want to use it in main and a file called menus.c and declare it in menus.h I assume. We wan

Answer 1

It's often helpful to use typedef with function pointers, so you can name the type to something descriptive:

typedef void (*MenuFunction)(int);

Then you would have a global variable of this type, probably in menus.c, and declared (with extern) in menus.h:

static void my_first_menu_function(int x)
{
  printf("the menu function got %d\n", x);
}

MenuFunction current_menu = my_first_menu_function;

From main.c, you can then do:

#include "menu.h"

current_menu(4711);

to call whatever function is currently pointed at by current_menu.

Answer 2

A function pointer is still a pointer, meaning it's still a variable.

If you want a variable to be visible from several source files, the simplest solution is to declare it extern in a header, with the definition elsewhere.

In a header:

extern void (*current_menu)(int);

In one source file:

void (*current_menu)(int) = &the_func_i_want;

Answer 3

A pointer function itself does not have a function definition. It's nothing more than a pointer to a type, the type being specified by the return type of the function and the parameter list. What you need to do is define a function with the same parameter list and return type, then use your pointer function to hold that function's address. You can then call the function through the pointer.