Path: utzoo!attcan!uunet!lll-winken!lll-lcc!ames!umd5!uflorida!novavax!proxftl!bill From: bill@proxftl.UUCP (T. William Wells) Newsgroups: comp.lang.c Subject: Re: Noalias trivia question Summary: humans are not computers (probably) Message-ID: <314@proxftl.UUCP> Date: 13 Jun 88 23:51:26 GMT References: <14522@brl-adm.ARPA> Organization: Proximity Technology, Ft. Lauderdale Lines: 22 In article <14522@brl-adm.ARPA>, dsill@nswc-oas.arpa (Dave Sill) writes: > You are implying that programmers can solve unsolvable problems but > that programs cannot, which is simply not true. Actually, you should keep your referents straight. I might be implying that humans can solve problems that are unsolvable by COMPUTERS. The truth of that is a matter of conjecture. This of course ignores the fact that aliasing is a property of the DESIGN of the program, not just of the program itself. It is entirely possible to design a program which has some particular aliasing property which can't be found by inspecting the code. Consider this contrived example: scanf("%d %d", &i, &j); p = &a[i]; q = &a[j]; Can p and q point to the same object? In the general case, yes. However, the programmer might intend this to be in a system where the two numbers can never be the same. So, the noalias keyword would add information that is not present in the program.