Re: [RFC][PATCH v2 3/6] Implement the %OB specifier - alternative month names (bug 10871)

[Paul Eggert <eggert@cs.ucla.edu>]

On 06/01/2016 02:51 PM, Rafal Luzynski wrote:
> I'm afraid that providing full backward compatibility is impossible.
> If an application calls strftime("%B",...) or nl_langinfo(MON_...)
> we have no way to tell if this particular application actually
> meant "%OB" and ALTMON_... or it is indeed correct for it to call
> "%B" and MON_.

Of course glibc cannot tell for sure; it is not an oracle. However, if 
glibc uses the old behavior when the application links to the old 
strftime, and the new behavior when the application links to the new 
strftime, then old executables will have the same old behavior even when 
linked to new glibc, which was Dmitry's point.

Even if the new behavior is standardized and is more likely to be what 
the user wants, there will almost surely be cases where the old behavior 
is preferable (if only to make regression tests pass :-), and the 
natural way to tell programmers about this is to say that old programs 
get the old behavior and new programs get the new one.