Re: glibc strerrorname_np

[Jonny Grant <jg@jguk.org>]

On 08/11/2021 08:36, Florian Weimer wrote:
> * Jonny Grant:
> 
>> I noticed on the man page it may return NULL, which is a shame, as then it means we always need to check that before using in every printf etc :-
>>
>> printf("err %s\n", strerrorname_np(myerr)?strerrorname_np(myerr), "Unknown err");
> 
> We can add %#m to printf for this use case.  It would print the errno
> constant if known, or a number otherwise.  To use it, errno needs to be
> assigned before calling printf.  Printing multiple error codes would not
> be possible directly, but such usage is quite rare.

Hi Florian

I couldn't find a reference description of %#m - May I ask if you have a link? I see %m is a GNU printf extension.

Still feels risky, relying on all calling code that currently uses strerror() to also change from %s to %#m to avoid a NULL ptr SEGV.

With kind regards
Jonny