Function pointer in struct, taking the struct as argument in C

Question

How can I use function pointers in a struct using the struct as argument?

I have this:

typedef struct button {
    char SizeUnit;
    char Status;
    
    int Width;
    int Height;
    
    
    char *Text;
    Color TextColor;
    Color BGColor;
    Color BorderColor;
    int BorderWidth;
    
    
    void (*ActionL)(button *bt);
    void (*ActionR)(button *bt);
    void (*ActionM)(button *bt);
    
    void (*Hover) (button *bt);
    void (*draw) (button *bt);
} button;

How can I get this working?

Answer 1

The "effects" of the typedef (the symbol being recognized) are not available in the struct itself.

You have two options:

1. Simply reference struct button when it comes to define function pointers

    void (*ActionL)(struct button *bt);`
   

2. Write the typedef before the struct defintion (forward declaration):

    typedef struct button_s button_t;
   
    typedef  struct button_s {
        char SizeUnit;
        char Status;
   
        int Width;
        int Height;
   
        char *Text;
        Color TextColor;
        Color BGColor;
        Color BorderColor;
        int BorderWidth;
   
        void (*ActionL)(button_t *bt);
        void (*ActionR)(button_t *bt);
        void (*ActionM)(button_t *bt);
   
        void (*Hover) (button_t *bt);
        void (*draw) (button_t *bt);
    } button_t;
   

   Here I used a convention with a trailing _s for the struct before the typedef and _t for the newly defined type.