On 02/22/2012 03:01 PM, Linda Walsh wrote: > My question had to do with an unqualified wint_t not > unsigned wint_t and what platform existed where an 'int' type or > wide-int_t, was, without qualifiers, unsigned. I still would like > to know -- and posix allows int/wide-ints to be unsigned without > the unsigned keyword?
'int' is signed, and at least 16 bits (these days, it's usually 32). It can also be written 'signed int'. 'unsigned int' is unsigned, and at least 16 bits (these days, it's usually 32). 'wchar_t' is an arbitrary integral type, either signed or unsigned, and capable of holding the value of all valid wide characters. It is possible to define a system where wchar_t and char are identical (limiting yourself to 256 valid characters), but that is not done in practice. More common are platforms that use 65536 characters (only the basic plane of Unicode) for 16 bits, or full Unicode (0 to 0x10ffff) for 32 bits. Platforms that use 65536 characters and 16-bit wchar_t must have wchar_t be unsigned; whereas platforms that have wchar_t wider than the largest valid character can choose signed or unsigned with no impact. 'wint_t' is an arbitrary integral type, either signed or unsigned, at least as wide as wchar_t, and capable of holding the value of all valid wide characters and the sentinel WEOF. Like wchar_t, it may hold values that are neither WEOF or valid characters; and in fact, it is more likely to do so, since either wchar_t is saturated (all bit values are valid characters) and thus wint_t is a wider type, or wchar_t is sparse (as is the case with 32-bit wchar_t encoding Unicode), and the addition of WEOF to the set does not plug in the remaining sparse values; but using such values has unspecified results on any interface that takes a wint_t. WEOF only has to be distinct, it does not have to be negative. Don't think of it as 'wide-int', rather, think of it as 'the integral type that both contains wchar_t and WEOF'. You cannot write 'signed wint_t' nor 'unsigned 'wint_t'. -- Eric Blake ebl...@redhat.com +1-919-301-3266 Libvirt virtualization library http://libvirt.org
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