[Top][All Lists]

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

RE: [avr-gcc-list] A couple GCC warnings I would like to understand / ge

From: larry barello
Subject: RE: [avr-gcc-list] A couple GCC warnings I would like to understand / get rid of...
Date: Thu, 22 Jan 2009 10:17:07 -0700

the compiler is complaining because you have an extra or a missing "const"
in your structure definitions.  There is a mismatch between your flash
declaration and the type of pointer within your struct.  Probably adding a
const keyword to the pointer within your struct and removing the const in
your declaration will fix the problems.

-----Original Message-----
From: address@hidden
[mailto:address@hidden On Behalf Of
Vincent Trouilliez
Sent: Thursday, January 22, 2009 8:20 AM
To: address@hidden
Subject: [avr-gcc-list] A couple GCC warnings I would like to understand /
get rid of...


I am having a couple GCC warning I would like to understand and
hopefully clear with a graceful modification of my code, if anyone can

Basically it's to do with the structures I put in Flash, and the
pointers to these structures (which are themselves located in said

When I initialize the structure with constant data, GCC coughs about
the field where I store the pointer.

Then later in the code, when trying to retrieve/read that pointer and
use it, I also get a warning.

It has to be said that GCC actually understands what I want to do,
because it stored and retrieved the correct pointer value, and my
program works as expected. It's just that these warning are annoying
and of course, maybe I did do a mistake in the syntax, and that would be
the opportunity to learn a little something new today..

#1 warning: when storing pointer in Flash

Pointer is stored in structure "menu_main", and points to "menu_sub"
(structure of the same type). 

//target structure
const struct TMenu menu_sub PROGMEM = {

//struct holding the pointer
const struct TMenu menu_main PROGMEM = {
        {.... , &menu_sub,...},   <-------WARNING

The warning is:
"warning: initialization from incompatible pointer type"

I don't understand why it's incompatible. I the structure is define as

struct TMenu;

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

the pointer ptr is declared as a pointer to a structure of type TMenu,
and of course I initialize it with the address of such a structure
(&menu_sub), so... where is the incompatibility ? :-/

#2 warning: when retrieving/reading pointer from Flash

// declare pointers of same type as found in struture, 
// in order to read them from flash

void (*FncPtr)();
const struct TMenu      *SubPtr;

FncPtr = pgm_read_word( & (p->items[cursor].fptr) );
SubPtr = pgm_read_word( & (p->items[cursor].ptr) ); 

I get a identical warning for each of these lines/reads :

"warning: assignment makes pointer from integer without a cast"

Here for a change, I think I can, agree with GCC, since pgm_read_word
returns an integer, but what's the syntax to turns that back into the
pointer it once was ?!

Something like that ?

FncPtr = ( void  (*FncPtr)() )pgm_read_word( & (p->items[cursor].fptr) );

and similarly:

SubPtr = (*SubPtr)pgm_read_word( & (p->items[cursor].ptr) ); 

Tried, doesn't work...

A cyber beer offered to anyone with the answer :-)


Vince, still at the very bottom of the learning curve, brrr...

AVR-GCC-list mailing list

reply via email to

[Prev in Thread] Current Thread [Next in Thread]