Messages in this thread | | | Date | Tue, 25 Feb 2003 07:27:26 -0800 (PST) | From | Linus Torvalds <> | Subject | Re: [PATCH] s390 (7/13): gcc 3.3 adaptions. |
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On Tue, 25 Feb 2003, Andreas Schwab wrote: > |> > |> The point is that the compiler should see that the run-time value of i is > |> _obviously_never_negative_ and as such the warning is total and utter > |> crap. > > This requires a complete analysis of the loop body, which means that the > warning must be moved down from the front end (the common type of the > operands only depends on the type of the operands, not of any current > value of the expressions).
So? Gcc does that anyway. _Any_ good compiler has to.
And if the compiler isn't good enough to do it, then the compiler shouldn't be warning about something that it hasn't got a clue about.
> |> and anybody who writes 'array[5UL]' is considered a stupid git and a > |> geek. Face it. > > But array[-1] is wrong. An array can never have a negative index (I'm > *not* talking about pointers).
You're wrong.
Yes, when declaring an array, you cannot use "array[-1]". But that's not because the thing is unsigned: the standard says that the array declaration has to be a "integer value larger than zero". It is not unsigned: it's _positive_.
However, in _indexing_ an array (as opposed to declaring it), "array[-1]" is indeed perfectly fine, and is defined by the C language to be exactly the same as "*(array-1)". And negative values are perfectly fine, even for arrays. Trivial example:
int x[2][2];
int main(int argc, char **argv) { return x[1][-1]; }
the above is actually a well-defined C program, and 100% standards-conforming ("strictly conforming").
Linus
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