[avr-gcc-list] Re: invalid use of non-lvalue array

[René Liebscher]

Is this problem solved? (PSTR with C++)

I tried to change the PSTR macro to work around the problem.

It was

#define PSTR(s) ({static char __c[] PROGMEM = (s); __c;})

after changing it to

#define PSTR(s) ({static char __c[] PROGMEM = (s); &(*__c);})

it seems to work.
Maybe someone could check this, so it can be fixed in next versions of
avr-libc?

Kind regards
Rene Liebscher

> On Wed, 1 Oct 2003, E.Weddington wrote:
>
> > > I am trying to use avrgcc for a little bit of C++ and it seems
> > > that the trusty PSTR macro isn't so trusty when using C++ giving
> > > an error of "invalid use of non-lvalue array".
> > >
> > > Before I dive into it I wonder if anyone else out there has solved
> > > this one?
> >
> >
> > If you're using C++, be sure to read the FAQ:
> > <http://savannah.nongnu.org/download/avr-libc/doc/avr-libc-user-manual/FAQ.html#faq_cplusplus>
> >
> > Also, avr-gcc.exe is the C compiler. You'll want to use avr-g++.exe
> > which is the C++ compiler.
>
> I don't think that addresses the problem.
>
> I can easily reproduce this. The only way I could work around it was
> with this hack:
>
> -- begin example --
> #include <stdio.h>
> #include <avr/pgmspace.h>
>
> int dummy_putchar (char c) { return 0; }
>
> #define fprintf_PSTR(fp, fmt, args...) ({   \
>     static char pfmt[] PROGMEM = fmt;       \
>     fprintf_P (fp, pfmt, ## args);          \
> })
>
> int
> main (void)
> {
>     FILE *fp = fdevopen (dummy_putchar, NULL, 0);
>
>     fprintf_PSTR (fp, "Hello World!\n");
>
>     return 0;
> }
> -- end example --
>
> And avr-objdump shows that the string went to .text:
>
> Contents of section .data:
>  800100 20001001 0000                         .....
> Contents of section .text:
>  0000 0c944d00 0c946a00 0c946a00 0c946a00  ..M...j...j...j.
>  0010 0c946a00 0c946a00 0c946a00 0c946a00  ..j...j...j...j.
>  0020 0c946a00 0c946a00 0c946a00 0c946a00  ..j...j...j...j.
>  0030 0c946a00 0c946a00 0c946a00 0c946a00  ..j...j...j...j.
>  0040 0c946a00 0c946a00 0c946a00 0c946a00  ..j...j...j...j.
>  0050 0c946a00 0c946a00 0c946a00 0c946a00  ..j...j...j...j.
>  0060 0c946a00 0c946a00 0c946a00 0c946a00  ..j...j...j...j.
>  0070 0c946a00 0c946a00 0c946a00 0c946a00  ..j...j...j...j.
>  0080 0c946a00 0c946a00 0c946a00 48656c6c  ..j...j...j.Hell
>  0090 6f20576f 726c6421 0a001124 1fbecfef  o World!...$....
>  00a0 d0e1debf cdbf11e0 a0e0b1e0 e4e5fae0  ................
>
>
> I wonder if it would make sense to wrap all the *_P functions like
> this. Then you wouldn't need to use PSTR at all.
>
> Pros:
>
>   - All *_P calls become cleaner. E.g, printf_P(PSTR("foo")); becomes
>     printf_P("foo");
>
>   - Works in C and C++.
>
> Cons:
>
>   - Is gcc smart enough to catch multiple copies of a string? A little
>     experiment just now shows it's not.
>
>   - Makes it impossible to pass a ptr to a fmt string.
>
> Ted Roth