bug#32189: 27.0.50; GCC 7 warning due to -Wformat-truncation=2

[Philipp Stephani <p.stephani2@gmail.com>]

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Ken Brown <kbrown@cornell.edu> schrieb am Mi., 18. Juli 2018 um 21:44 Uhr:

>
>
> This doesn't work with GCC 7.  (Maybe it would work with GCC 8; the
> release notes say that it is better at avoiding false positives.)  For
> integer specifiers like "%ld", the only thing I've found that works
> without enlarging the buffer is to cast the argument to a smaller
> integer type.


You can't do that; %ld requires a long argument, and casting results in
undefined behavior.


> For float specifiers like "%3.1f", even using a small
> type doesn't seem to work.  For example:
>
> $ cat test.c
> #include <stdio.h>
> int
> main ()
> {
>    char buffer[16];
>    short a;
>    snprintf (buffer, 16, "%3.1f", a);
> }
>

This is undefined behavior, as %f requires a double argument.

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