Alexey ,
unsigned long test1(void *p)
{
return sizeof(*p);
}
TBH, I don't think that's legal --- I know of several compilers that
will refuse to compile it, and gcc -pedantic produces a warning, which
means it probably falls into the 'undefined behaviour' bucket of the
standard. I can't find anything that specifically talks about sizeof
void, but 6.3.2.2.1 prohibits doing *anything* with the result of an
expression of type void, which sort of applies here.
Of course, I'm thinking about this from the sparse-as-a-compiler point
of view, where you're probably more interested in replicating gcc's
behaviour.
This seems to be legal, and quite popular in the Linux kernel. GNU C defines
sizeof(void) being 1.And as it has the -Wpointer-arith flag, this kind of stuff
may be caught without sparse if deemed undesirable.
It is a constraint violation.
"The sizeof operator shall not be applied to an expression that has
function type or an incomplete type"
sentence 1118: c0x.coding-guidelines.com/6.5.3.4.html
void is an incomplete type that cannot be completed
sentence 524: c0x.coding-guidelines.com/6.2.5.html
In pre-C90 days, prior to the availability of void, char * was
often used in a context where void * is now used. Treating void
as being equivalent to char in some kind of compatibility mode
makes sense. It looks like the gcc maintainers have over stepped
the mark.
I have reported the bug in gcc. Track Bug: 38563
at: gcc.gnu.org/bugzilla
--
Derek M. Jones tel: +44 (0) 1252 520 667
Knowledge Software Ltd mailto:derek@xxxxxxxxxxxx
Source code analysis http://www.knosof.co.uk
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