Re: [HACKERS] new gcc 7.0.1 warnings

Pavel Stehule <pavel.stehule@gmail.com> writes:
> float.c:382:5: note: ‘snprintf’ output between 2 and 311 bytes into a
> destination of size 65
> float.c:618:5: note: ‘snprintf’ output between 2 and 311 bytes into a
> destination of size 129

That's kind of annoying.  I suppose the point is that the compiler can't
see what precision we're selecting, and with sufficiently large precision
the output could be that wide.  But actually the precision should be small
enough to make that OK.

Do the warnings go away if you add some explicit guard to the precision
variable, say like this:

            {
                int            ndig = DBL_DIG + extra_float_digits;

                if (ndig < 1)
                    ndig = 1;
+               if (ndig > 50)
+                   ndig = 50;

                snprintf(ascii, MAXDOUBLEWIDTH + 1, "%.*g", ndig, num);
            }

If not, I guess we could increase the size of the palloc'd strings,
but that seems wasteful.

                        regards, tom lane