extern char *foo vs. extern char foo[]

[Stephen Clamage]

In article <1990May30.001219.23564 at uunet!unhd> rg at unhd.unh.edu.UUCP (Roger Gonzalez ) writes:
>
>A little history: I know C inside and out, and don't need any "I think"s.

Evidently not.

>According to K&R, there should be no difference between the two extern
>defs in my subject header.  In fact, the second form (char foo[]) should
>get translated into the first.

Not true.

>     char hello[100];
>     extern hello[];
In both declarations, hello means the address of an array.
hello is a (link-time) constant and may not be assigned to.

>     extern char *hello;
hello means the address of a variable which *contains* the address of an
array (or of a variable, which would be an array of size 1).
hello may be assigned to, so as to point to another array.

>So.  Why are my compilers so stupid?  Do others
>behave the same way, or am I just unfortunate enough to have lousy software?
Other compilers better behave the same way, since the language definition
requires it.

It is a common misunderstanding that arrays and pointers are in some sense
"the same thing".  This is one case where they are not the same thing.  The
difference is discussed in Chapter 5 of old original K&R, and this difference
has not changed.  It is still a difference in ANSI C.
-- 

Steve Clamage, TauMetric Corp, steve at taumet.com