So in effect the standard committee have chosen to allow any program which invokes any undefined behavior to behave arbitrarily without diagnosis?
This is a good thing? [ curiously can't find any actual reference stating that integer overflow is specifically results in undefined behavior, although it's obviously ill defined? although can find reference that a dereference of an overflowed pointer is undefined? ] > From: "Joseph S. Myers" <[EMAIL PROTECTED]> > On Sat, 18 Jun 2005, Paul Schlie wrote: > >> [#1] Behavior, upon use of a nonportable or erroneous >> program construct, of erroneous data, or of indeterminately >> valued objects, for which this International Standard >> imposes no requirements. Permissible undefined behavior >> ranges from ignoring the situation completely with >> unpredictable results, to behaving during translation or >> program execution in a documented manner characteristic of >> the environment (with or without the issuance of a >> diagnostic message), to terminating a translation or >> execution (with the issuance of a diagnostic message). > > You appear to have chosen to misquote again. In this case, you've taken > the C90 version of the wording but with a paragraph number from C99 (C90 > did not have paragraph numbers). Perhaps you cannot grasp the generality > of "no requirements"? A few examples are given, but "no requirements" > means that the program can behave completely inconsistently if it involves > undefined behavior. > >> [#3] The implementation must successfully translate a given >> program unless a syntax error is detected, a constraint is >> violated, or it can determine that every possible execution >> of that program would result in undefined behavior. > > This looks like a completely fabricated quote to me. If it comes from > C99, state the subclause and paragraph numbers (in C99 as amended by TC1 > and TC2). It certainly doesn't seem to be in the plain text version of > C99+TC1. In general, state where you are quoting rather than just > claiming particular text you've just written is relevant. > >> Which again is specific to that which is defined, as it requires the >> successful (and presumably conformant) translation of the program unless >> the implementation can prove the whole program is itself would have an >> undefined behavior (reinforcing the notion that the language's semantics >> remain in force even in the presence of a expression with undefined >> semantics). > > "no requirements" means that *any* translation conforms in the case of > undefined behavior. Only those executions not involving undefined > behavior have any requirements. > > -- > Joseph S. Myers http://www.srcf.ucam.org/~jsm28/gcc/ > [EMAIL PROTECTED] (personal mail) > [EMAIL PROTECTED] (CodeSourcery mail) > [EMAIL PROTECTED] (Bugzilla assignments and CCs)
