On 06/22/2017 09:05 AM, Pico Geyer wrote:
On Thu, Jun 22, 2017 at 4:51 PM, Jonathan Wakely <jwakely.gcc@xxxxxxxxx> wrote:
On 22 June 2017 at 15:31, Jonathan Wakely wrote:
Because the -Wformat-overflow warnings are new in GCC 7, i.e. GCC got
better. See https://gcc.gnu.org/gcc-7/changes.html#c-family
Oops, I meant -Wformat-truncation not -Wformat-overflow. I copy&pasted
the wrong option.
I didn't even notice :-|
I forgot to follow up on the comment in the code.
Any idea why commenting out the " if ( amt == 0 ) return " makes the
warning go away?
I can't think of a reason.
It's an effect of the logic used by the warning. The conditional
constrains the range of values the variable amt may have when it's
passed to snprintf to a subrange of the variable's type. This is
used by the warning to indicate that the caller made an attempt
to prevent the function from truncating an excessively large value
but didn't go quite far enough to. With the conditional removed
the variable has no such range associated with it (all GCC can
tell is that it can have any value of its type). That's
(conservatively) taken to mean that the variable is constrained
somewhere else in the program that GCC can't see, and so the
warning is more relaxed. It was done to avoid excessive false
positives. With -Wformat-truncation=2 the logic is the same
regardless and so the warning triggers both with and without
the conditional.
Martin
