Re: [Caml-list] ocamlc -output-obj problems

[skaller <skaller@users.sourceforge.net>]

On Tue, 2005-11-15 at 14:01 +0100, Alessandro Baretta wrote:
> Jonathan Roewen wrote:
> > It's all my fault. It's always all my fault ;D
> > 
> > char **argv = ... => char *argv[] = ...
> 
> Please excuse my stupidity: what's the difference?

The first case says argv is a pointer to a pointer.
The second says it is an array of pointers.

When you pass an argument of the second type to a
function, it *decays* to the first type: there is 
no difference accessing the two.

But there is a HUGE difference in the data structure
created by a declaration -- the first reserves
exactly one word of storage. The second reserves
an actual array. Watch:

This compiles:

char * a[] = {"A","B"};
char ** b = a; 

This does NOT compile:

char * a[] = {"A","B"};
char ** b = {"A","B"};
a.c:2: warning: initialization from incompatible pointer type
a.c:2: warning: excess elements in scalar initializer
a.c:2: warning: (near initialization for ‘b’)

Note also: ++a is illegal, a is a constant. You cannot
increment an array. But ++b is allowed, it is merely
a pointer to the first element of the array.

And now notice Jonathan wrote:

> char **argv = ... => char *argv[] = ...

with an = in there. Looks like his gcc is broken :)

-- 
John Skaller <skaller at users dot sf dot net>
Felix, successor to C++: http://felix.sf.net