> Robert Dewar wrote: >> Paul Schlie wrote: >>> Brooks Moses wrote: >>> <http://gcc.gnu.org/ml/gcc/2007-01/msg01119.html> ... >>> Does that logic work for you? >> >> no, as although a variable's value may not have been previously defined >> within the context of a particular program, a variable's access semantics >> are orthogonal to what ever value may result from that variable's access; >> and thereby although it's resulting value may be indeterminate, successive >> logical references must sensibly be presumed to yield equivalent values >> baring the variable being declared as being volatile, or having an >> intervening assignment. > > Paul, you really really need to read the C standard. It's beginning > to sound as though you haven't, since you keep making things up that > are just not justified by the standard. >> >> (there seems to be too much desire to arbitrarily justify anything at the >> drop of a hat given an opportunity to associate it directly or indirectly >> with an undefined behavior, regardless of its sensibly > > There is no question about what the C standard makes undefined here. > That of course does not preclude giving it defined semantics in a > particular language, thus effectively extending the language, but the > C standard committee in making something undefined is very deliberately > deciding that it is more appropriate than making it implementation > defined. > > In the case of access to uninitialized variables in C, no one (or > almost no one, I realize you are an exception), would favor trying > to make this implementation defined. The only way you will get this > is by creating a variant of gcc for your own use yourself :-) > > Now a special mode for debugging which does initialize all > uninitialized variables to a specified value, a la GNAT's > pragma Initialize_Scalars, could be useful. But anyone relying > on Paul Schlie semantics for uninitialized variables is writing > rubbish instead of C!
[ISO/IEC 14882-2003] Section 8.5, paragraph 9 says: "... if no initializer is specified for a nonstatic object, the object and its subobjects, if any, have an indeterminate initial value" Thereby it seems fairly clear to me that although an uninitialized variable has an indeterminate INITIAL value, all subsequent accesses to that variable will yield that INITIAL value until otherwise programmatically modified. Thereby x ^= x is correspondingly well defined if non-volatile as originally asserted.
