> From: Robert Dewar <[EMAIL PROTECTED]> > Paul Schlie wrote: > >> As in my mind, the semantics of foo() dictate that it print the value of >> the storage location which was allocated to the variable "a", where unless >> "a" is initialized with an explicit value, may be arbitrary. So I've got no >> problem with arbitrary results or behavior, I just simply believe they are >> implicitly constrained to the remaining rules of the language, i.e. all >> side-effects must be expressed upon reaching a sequence point which >> logically bounds the effects of the evaluation of any expression. > > This cannot be formalized, and is not what the standard says. The fact that > you believe it is interesting (though I don't think you can write a formal > description of what you believe in C standard terms), but we operate by what > the standard formally says, not by what one person informally believes. > >> (where if an undefined behavior it did delete the program being executed it >> wouldn't resume execution beyond the next sequence point, but if it does, it >> must continue to abide by the languages rules regardless of the resulting >> side effects from the preceding behaviors) > > Sequence points simply do not have this semantics. If they did, then nearly > all useful optimizations would be prohibited. You are essentially positing > a model in which the state at every sequence point is not only defined by > the standard, but must be reflected in the implementation with no use of > as-if semantics. I don't see this as meaningful, and I don't think this can > be formalized. I am quite *sure* that it is undesirable.
- You may be correct, although it's not obviously the case? (As requiring all undefined behavior be encapsulated between sequence points already seems implied to me, as I don't see any explicit counter examples requiring otherwise. Nor do any optimizations which are obviously more useful than potentially counterproductive seem to require the violation of C's sequence point semantics?)
