[avr-libc-dev] Printf %S printing from PROGMEM not functional, compiler error

[Joerg Wunsch]

error: format '%S' expects argument of type 'wchar_t*', but argument 2
has type 'const char*' [-Werror=format=]
printf("%S:%u\n", name, i);

Then do as suggested, and turn off compiler warnings (and -Werror) for
this.

And "just for fun" I would like to know how to print wide characters

You can't. avr-libc doesn't implement wide chars in any way.

[Joerg Wunsch]

Post by Joerg Wunsch

error: format '%S' expects argument of type 'wchar_t*', but argument 2
has type 'const char*' [-Werror=format=]
printf("%S:%u\n", name, i);

Then do as suggested, and turn off compiler warnings (and -Werror) for
this.

Sorry, I've been sick at the weekend, so my previous reply was a
little terse.

In general, the C standard reserves lowercase formatting letters for
future standardized conversions, but leaves other characters (so
namely uppercase letters) for "extensions".

Thus, avr-libc's use of %S for progmem strings is fully standards
compliant. It's GCC here that applies wrong assumptions. It would be
cool if we could somehow "tune" that in the avr-libc printf()
prototype (to avoid the pointless warning), but I'm not enough of a
GCC expert on that.

Post by Joerg Wunsch

And "just for fun" I would like to know how to print wide characters

You can't. avr-libc doesn't implement wide chars in any way.

The standard's format specifier for a wide character string is "%ls".

That's why GCC's notion of %S is just another kind of an extension to
the standard only. We've picked %S for progmem strings, since we
don't support wide characters anyway, and it seemed to be the most
logical extension.