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Asked: 2026-05-15T19:17:41+00:00

I’ve got some structs to initialise, which would be tedious to do manually. I’d

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I’ve got some structs to initialise, which would be tedious to do manually. I’d like to create a macro that will help me with it… but I’m not sure the C preprocessor is good enough for this.

I’ve got structs which represent menus. They consist of function pointers only:

typedef uint8_t (*button_handler) (uint8_t);
typedef void (*pedal_handler) (void);
typedef void (*display_handler) (void);
typedef void (*menu_switch_handler) (void);

#define ON_BUTTON(x) uint8_t menu_frame_##x##_button (uint8_t button)
#define ON_PEDAL(x) void menu_frame_##x##_pedal (void)
#define ON_DISPLAY(x) void menu_frame_##x##_display (void)
#define ON_SWITCH(x) void menu_frame_##x##_switch (void)

typedef struct menu_frame {
   button_handler on_button;
   pedal_handler on_pedal;
   display_handler on_display;
   menu_switch_handler on_switch;
} menu_frame;

That allows me to write the functions and separate functions as (.c file):

ON_BUTTON(blah) { ... }

and menus as (.h file):

ON_BUTTON(blah);
ON_DISPLAY(blah);
menu_frame menu_frame_blah = {
   menu_frame_blah_button,
   NULL,
   menu_frame_blah_display,
   NULL
};

Is there any way I can fold the menu definition into one define? I could do something that expands MENU(blah, menu_frame_blah_button, NULL, menu_frame_blah_display, NULL) of course, but is there any way to:

  • make it shorter (NULL or some name)
  • remove the need of ON_BUTTON(...); from before the struct

Ideally, I’d like MENU(blah, button, NULL, display, NULL) to both define the handlers and the menu struct itself. I don’t know for example how to prevent expanding the last term into ON_SWITCH(NULL).

Or maybe I should approach it from some other way?

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1 Answer

  1. Editorial Team

    You cannot do conditional macro expansion in C, so that your macro would be expanded differently depending on the arguments, as in: you cannot use #if within macro definition.

    I guess the best you could get would be something like MENU(blah, ITEM(blah,button), NULL, ITEM(blah,display), NULL), and you still need a separate set for prototypes because of lack of conditional expansion.

    Personally, I would write a simple script to generate that sort of boilerplate C code. One that would understand your desired syntax. In Python or whatever suits you best…

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