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Re: Is this a compiler bug?


On Mon, 2014-09-22 at 16:32 +0200, Jakub Jelinek wrote:
> On Mon, Sep 22, 2014 at 10:22:59AM -0400, David Malcolm wrote:
> > On Sun, 2014-09-21 at 22:15 -0700, Andrew Pinski wrote:
> > > On Sun, Sep 21, 2014 at 8:08 PM, Steve Kargl
> > > <sgk@troutmask.apl.washington.edu> wrote:
> > > > On Sun, Sep 21, 2014 at 07:57:45PM -0700, Andrew Pinski wrote:
> > > >> On Sun, Sep 21, 2014 at 6:56 PM, Steve Kargl
> > > >> <sgk@troutmask.apl.washington.edu> wrote:
> > > >> > + is a binary operator.  0x3ffe is a hexidecimal-constant according
> > > >> > to 6.6.4.1 in n1256.pdf.  63 is, of course, a decimal-constant.
> > > >>
> > > >>
> > > >> This is before tokens happen and during lexing of the program.
> > > >> e+64 is exponent-part see 6.4.4.2.
> > > >
> > > > 6.4.4.2 applies to floating point constant.
> > > > 6.4.4.1 is for integer constants.
> > > 
> > > Nope again, this time from bug 3885:
> > > Strange as it may seem, the behavior is correct, and mandated by the C
> > > Standard.  0x00E-0x00A is a single preprocessor token, of type
> > > pp-number, and it must become a single compiler token, but it can't.
> > > The gotcha is the `E-' sequence, that makes it seem like the exponent
> > > notation of floating-point constants.
> > > 
> > > Looks like this is a common misunderstood part of C.
> > 
> > If people tend to get this wrong, should we issue a warning for it?
> 
> We already diagnose it, with an error actually, not warning:
> error: invalid suffix "+63" on integer constant
> etc.
> Just apparently people are surprised when the compiler diagnoses it.
> So perhaps some extra note explaining it (== hint how to fix that).

I've filed PR63337 with some ideas on how the error message could be
improved for this case.



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