On Mon, 2011-07-25 at 19:58 -0400, Arnaud Lacombe wrote: > Hi, > > [...] > > In which case the warning is fully valid. I'm not sure what's the C > > standard guarantee in term of conditional test order. > I'd assume that the following apply: > > 6.5 Expressions > > 3 The grouping of operators and operands is indicated by the > syntax.72) Except as specified > later (for the function-call (), &&, ||, ?:, and comma operators), > the order of evaluation > of subexpressions and the order in which side effects take place are > both unspecified. > > > in which case gcc is free to do whatever it wants :( No it does not! Read what you wrote: "Except as specified later (for the function-call(), &&, ||, ?:...)" && and || must be short cuts. That is, it must evaluate the earlier statements before the later, and exit when it can. We use that all over the kernel (and in all C code): if (ptr && ptr->field) If it were to switch that to: if (ptr->field && ptr) we would have segfaults everywhere. This looks like a serious gcc bug. -- Steve
