RE: [avr-gcc-list] A couple GCC warnings I would like tounderstand/ get rid of...

[Weddington, Eric]

> -----Original Message-----
> From: 
> address@hidden 
> [mailto:address@hidden
> org] On Behalf Of Vincent Trouilliez
> Sent: Saturday, January 24, 2009 5:25 PM
> To: address@hidden
> Subject: Re: [avr-gcc-list] A couple GCC warnings I would 
> like tounderstand/ get rid of...
> 
> > ... where I initialize a pointer with "&dummy_func"
> 
> errata, I meant &menu_sub not &dummy_func of course...
> 


I'd like to point something out.


The structure type definitions are this:

struct TMenuItem {
        char            text[20];
        const struct Tmenu      *ptr;
        void (*fptr)();
};

struct TMenu {
        uint8_t nb;                             
        char            title[21];              
        const struct TMenuItem  items[];
};

Your original data structure initialization is this:

struct TMenu menu_main PROGMEM = {
        6,
        "___Main Menu________",
        { 
                {"Item 1             ",&menu_sub,NULL},
                {"Item 2             ",&menu_sub,NULL}
        }
};

Which means that you have the NULL and the &menu_sub *reversed* according to 
your data structure layout, and then on top of this your &menu_sub is the 
*wrong data*! The structure is looking for a pointer to a function, and you are 
giving it a pointer to another struct TMenu type.

This is why it needs to be changed to this:

struct TMenu menu_main PROGMEM = {
        6,
        "___Main Menu________",
        { 
                {"Item 1             ",NULL,&dummy_fnc},
                {"Item 2             ",NULL,&dummy_fnc}
        }
};

The other two lines that I changed, were these:

        FncPtr = (void (*)(void))(pgm_read_word( & (p->items[0].fptr) ));
        SubPtr = (const struct TMenu *)(pgm_read_word( & (p->items[0].ptr) ));

The reason is that the pgm_read_word macro returns a uint16_t type which you 
are then assigning to variables that are pointer types (pointing to two 
different things). All you needed to do was to typecast the result of 
pgm_read_word() (as I did above) to match the type of the variable that you are 
assigning to.

HTH,
Eric Weddington