[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Old Index]
Re: must use gcc builtin?
On Tue, 21 Feb 2012, James K. Lowden wrote:
Just for fun, I thought I'd try compiling Gary Capell's
"wily" editor. The code is from 2006, hardly ancient. Its
library manipulates a va_list as pointer using assignment and
I believe that the definition of "undefined behavior" in section
3.4.3 of the C99 standard applies:
behavior, upon use of a nonportable or erroneous
program construct or of erroneous data, for which this
International Standard imposes no requirements".
I believe that using a va_list as if it were a pointer, and doing
arithmetic on it, is something on which the Standard imposes
no requirements, and that the resulting behaviour is therefore
Section 4 paragraph 2 is also pretty clear that "the omission of
any explicit definition of behaviour" also counts as undefined
behaviour. So it's not necessary for the Standard to say "if you
do <X> then the behaviour is undefined"; if the Standard merely
does not talk about <X> at all, the the behaviour if you do <X> is
I can't #undef __GNUC__. Do we really want to require the use
of builtins? I'd like a knob to compile idiomatic C, especially
*good* idiomatic C.
In my world, code that invokes undefined behaviour is not good
does not define a type for va_list. Assuming it's a pointer
might be nonportable, but it's not prohibited by the standard.
The standard hardly ever prohibits a program from doing something
--apb (Alan Barrett)
Main Index |
Thread Index |