On Wed, Sep 05, 2018 at 12:01:59PM -0700, [email protected] wrote:
> Right now the printf(3) family of manpages make no reference to errno.
> Glancing at __vfprintf, it appears that most of the erroneous paths do
> set errno.
Most, but not all. Stating it will set errno in all error cases is
not right.
-Otto
>
> Should the manual be amended to reflect this behavior, so that users
> have a documented way to determine the cause of failure in such cases?
>
> Note this is a smaller concession than a full ERRORS section to
> enumerate error codes, which would pin down the error API, making it
> hard to change without user breakage. errno is still useful without
> this section thanks to libc functions like strerror(3) and err(3).
>
> The intended effect on userspace developers is to encourage picking
> warn(3) over warnx(3) when logging, and other similar choices.
>
>
> Index: lib/libc/stdio/printf.3
> ===================================================================
> RCS file: /cvs/src/lib/libc/stdio/printf.3,v
> retrieving revision 1.74
> diff -u -p -u -r1.74 printf.3
> --- lib/libc/stdio/printf.3 13 Oct 2015 12:25:04 -0000 1.74
> +++ lib/libc/stdio/printf.3 5 Sep 2018 18:28:33 -0000
> @@ -642,7 +642,9 @@ a field; if the result of a conversion i
> field is expanded to contain the conversion result.
> .Sh RETURN VALUES
> For all these functions if an output or encoding error occurs, a value
> -less than 0 is returned.
> +less than 0 is returned and the global variable
> +.Va errno
> +is set to indicate the error.
> .Pp
> The
> .Fn printf ,
