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

[Dave Hansen]

From: Bob Paddock <address@hidden>
[...]
> What I've never understood at all is why are characters signed
> in any case?    What exactly is the meaning of a negative-letter-"A"?

It's all hysterical raisins.

The earliest C compilers made char signed by default because ASCII only 
requires 7 bits, and signed operations on 8-bit values on the target 
platforms were less expensive than unsigned.

As C proliferated before there was a standard, many compilers followed the 
practice, even if there was no difference between signed and unsigned 
operations.  However, if unsigned operations were less expensive, many 
compilers made char unsigned by default.

When the C standards committee met, one of their charters was to codify 
existing practice.  Since both signed and unsigned plain char were in common 
use at the time, the committee allowed either, so long as an implementation 
defined which it used.

IMHO this was an error on the committee's part.  As it is, the plain char 
type is almost useless, but you're essentially required to use it, since, 
for example, string literals point to arrays of plain char.  Furthermore, 
combined with the new (with the original standard) "value preserving" 
automatic promotion rules, signed char types are the source of many 
confusing promotion errors.

As it is, we're stuck with it, and since avrgcc has used signed chars by 
default for many years, the only reason to change to unsigned would be code 
efficiency gains, i.e., if operations on unsigned char were much less 
expensive than operations on signed char.  I haven't looked into it deeply, 
but I don't think that's the case for the AVR architecture.

> It would be better to code to stdint.h, than
> rely on any ambiguous compiler switches/standard-C 'undefined' issues.

For applications written for an 8-bit micro, such as the AVR, where you want 
tight control on such things, this is true.  It is not true for all 
applications that might be written in C, however.  And you really have no 
choice when it comes to using the standard library or string literals: 
you're stuck with plain char for those.

Regards,

  -=Dave

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