TITLE: signedness of char

(Newsgroups: comp.std.c++, 8 Jan 97)

MIKAEL: d96-mst@nada.kth.se (Mikael Ståldal)

>The signess of plain char is not defined in the standard. What are the
>resons for not mandating it to be unsigned?


CLAMAGE: Steve Clamage, stephen.clamage@eng.sun.com, 8 Jan 97

From the beginning in C, the signedness of 'char' was left up to the
implementation. The reason was that extending a char to an int ought
to be an efficient operation, and computers varied (and still vary)
in whether unsigned or signed extension was more efficient. On some
machines it makes no difference. On others, the "wrong" kind of
extension takes 3 instructions. When you consider that C extends
chars to ints all over the place, particularly for most standard library
functions, that is an important consideration.

Although some implementations of C allowed it earlier, Standard C
allows you to specify a character type as specifically signed or
unsigned.

Digression: IMHO, the whole thing was ill-considered. A 'char' ought to
be a character in the character set, and not a "tiny integer". If you want
the language to have a "tiny integer" or a "byte" type, 'char' should
not be overloaded for those purposes. If that principle had been adopted
in C (as it was in Pascal 8 years before K&R1), we would not need to
have these interminable discussions about behavior and implementation
of type char. End of digression.

If C++ mandated a signedness or implementation for type char, it would
break C compatibility. In addition, it would require an inefficient
implementation of char on some systems. IMHO, this is one of many
features of C++ that must remain suboptimal (or broken) in C++
because compatibility is considered more important than abstract
(or concrete) notions of good language design.