[RFC] Strftime return value when S is a null pointer

[Paolo Carlini]

Hi,

I'm working on a libstdc++-v3 problem report. In order to fix it 
properly, I must
be sure about the value returned by strftime when S is a null pointer. 
Indeed,
according to the glibc docs

    "If S is a null pointer, `strftime' does not actually write
     anything, but instead returns the number of characters it would
     have written."

and this is rather nice (not nice as snprintf, but, anyway). The problem 
is that I
cannot find in C99 anything *mandating* this specific behavior.

Is it a glibc specific feature? In case, as far as glibc is concerned, 
can we rely upon
it for all the recent, current (and, likely, future) releases?

Thanks in advance,
Paolo.