Re: Array operator overloading from typedef?

James Kanze <>
Mon, 20 Apr 2009 01:32:52 -0700 (PDT)
On Apr 20, 5:35 am, "Jeff M." <> wrote:

Sorry if this is a fairly simple thing... I'm an ol' C timer,
not much of one for C++. But, I do have an interesting problem
here, and not sure if there's a solution to it [the way I'd
like]. Perhaps someone here can show me how - or perhaps
present me with other options on getting the behavior I'm
looking for.

Also, let me apologize in advance for the "cryptic" post. The
codebase is rather large that I'm working in, and instead of
pasting lots of code, I'll first try just a simplified
explanation (and hopefully I'll do a decent job).

I have a type that's - for all intensive purposes - a kind of
variant. We'll call this class Foo. There's nothing really
special in it, except that it ends with byte[0], and we always
allocate more space for the data that Foo manages.

struct Foo
    // stuff

    char byte[0];

This isn't legal C nor legal C++. Arrays can't have 0 as a
dimension. And the only think you could do with it if you could
declare it is take the address of one past the end.


Now, we always have a pointer to a Foo - never a reference or
a static allocation. And because Foo is actually hidden a bit,
there's a different type that is exposed to all the other
code... let's call it Thing:

typedef Foo* Thing;

Now, what I'd _like_ to do is overload the [] operator in such
a way that, given a Thing, I can index into Foo::byte and get
what I need. I can obviously put the [] operator inside of

The only place you can put an operator[] is inside a class. C++
requires it to be a non-static member function. But you still
can't declare byte to have a dimension of 0, and if you declare
it to have a dimension of 1, you can't access beyond the first
element without incurring undefined behavior.

but then I end up with a lot of code that looks like

Thing p = ... ;

Which isn't exactly very readable.

So make Thing a class which wraps Foo, dand define the
operator[] there.

James Kanze (GABI Software)
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