printf field width argument handling

[Eric Blake]

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According to Corinna Vinschen on 11/25/2009 1:50 AM:
> I don't think we have to return with errno set, either.  I'm not even
> sure if we should change the behaviour at all, given that practically
> all BSD-based systems behave that way.

POSIX is explicit that use of an improperly formed specifier (such as
%**s) gives unspecified results; it permits but does not require failure
with EINVAL, and returning successfully after printing an extremely huge
field width still qualifies as a valid action for unspecified results.
Besides, an invalid string is something you can audit for (after all, gcc
- -Wall catches this particular one if you did it via a compile-time string,
and if you are using arbitrary user input as a runtime-provided format
string, you are already vulnerable to %n exploits), so why bloat the code
to stop the user from doing something they should have already prevented
at compile time?

- --
Don't work too hard, make some time for fun as well!

Eric Blake             ebb9@byu.net
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