Re: [avr-gcc-list] New GCC warning - how to silence?

[David Brown]

Joerg Wunsch wrote:

> The issue is, any implementation will always have to implement it as
> either
>
> unsigned char == char != signed char
>
> or
>
> unsigned char != char == signed char.
>
> Yet, as the default signedness of char is not defined by the standard,
> any *portable* application has to be written as if
>
> unsigned char != char != signed char
>
> That's the entire point the warning is about, and that's why neither
> your compile-time option nor your suggested change to the compiler's
> default behaviour would avoid the warning.  Nor would they fix the
> broken (in terms of portability) application.

I agree with most of this.  It is more natural for most processors 
(small ones, anyway) to process chars as unsigned - sometimes 
comparisons with unsigned data are smaller and faster than with signed 
data (though not on the AVR).  Thus I explicitly use the 
"-funsigned-char" flag for all my targets.  But well-written C code 
*should* make the distinction between "char", which represents a 
character, and "unsigned char" and "signed char", which are the smallest 
unsigned and signed integer types.  They are different types, used for 
different purposes.

Anyone switching to a significantly new version of their compiler tools 
should expect that some things may change.  In this case, the compiler 
is now fussier about mixing the signedness of chars, and issues 
warnings.  The developer has three choices - they can stick to the older 
version of the compiler (which is normally the advisable thing to do 
with existing projects), they can turn off that specific warning (this 
is *exactly* why there are command-line options for disabling individual 
warnings), or they can correct their code.

It's important not to change the default "char" signedness - people *do* 
write code that uses "char" as a small signed integer.  They are writing 
bad code when they do so, but it is done nonetheless.  If it is to be 
changed, then it has to be done over two major versions, with current 
releases noting that "char" will change to unsigned in the future.  That 
at least gives people fair warning - just as is done when introducing 
any other incompatible changes.

mvh.,

David