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Re: using the interfaces in ctype.h
On 22-Apr-08, at 3:51 AM, Alan Barrett wrote:
Can anybody confirm the existence of compilers such that
signed char c = -1;
return isupper((unsigned char)c);
produces a warning which can be quieted by an additional cast to int,
return isupper((int)(unsigned char)c);
Potentially some compiler might complain about the unsigned char to
signed int promotion without the explicit (int) cast, though
apparently GCC doesn't (at least not so long as UCHAR_MAX <= INT_MAX).
I'll try to get access to IRIX and Solaris machines again to try
these. IIRC it was one of these I was seeing warnings from, and most
likely it was IRIX, perhaps with whatever sensible warning options
their compiler supports(*). Unfortunately that's the one I'm least
likely to be able to get access to again so anyone else who has access
to IRIX systems should try it.
(*) In Smail-3 I used the following on IRIX-6.x last time I tested it
CFLAGS="-Xa -g3 -O3 -fullwarn -diag_suppress 1184,1209,3201,3496"
BTW, can anyone say with any degree of certainty which, if any, C
implementations (hosted) will extend the sign when the value of a
"char *" pointer is assigned to a plain "int"? I.e. in "int i = *s;"
DMR says (in the second edition of "The C Programming Language", p.
44): "On some machines a char whose leftmost bit is 1 will be
converted to a negative integer ("sign extension")." In the first
edition he also said "(PDP11, for instance)". Harbison and Steele, in
"C A Reference Manual" say much the same too of course, though never
in exactly the context of using the result of indirecting a "char *"
pointer. DMR uses the "int c; char *s; while ((c = *s)) ..." idiom at
least once (p.156), though perhaps that was a mistake.
Greg A. Woods; Planix, Inc.
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