is "extern" ambiguous

[Karlos Mauvtaque]

no

"extern" always means "externally visible".

extern int	i;

declares an externally visible int with name i, it doesn't matter where
the declaration appears.  remember, the default storage class is "extern"
(section 10.2 of the C reference manual) so this is equivalent to

int	i;

similarly

extern int	poot();

or

int	poot();

declares an externally visible function returning int named poot, the
absence of a function body requires that one appear elsewhere.

the ambiguity is in the C compilers which float around.  some compilers
adopt the "restricted environment" (where the explicit appearance of
"extern" means that storage is allocated elsewhere), some just do
incorrect things.