C++Talk.NET

Alan McKenney · Guest

I cannot figure out how to forward declare a class
that
is in a namespace or nested in another class.

I like to define classes that relate to the definition
of a class within the class; for example, if I define
a table class StockTable, I like to define the
class that represents one row (or "entry") as
StockTable::Entry. E.g.,

class StockTable {
public:
class Entry { ... };
class Key { ... };
std::vector<Key, Entry> table;
....
};

I also like to define classes within namespaces, e.g.,

namespace A {
class C { .... };

};

I also like to use forward declarations, where
possible, to avoid having header files bring in more
definition than necessary. Thus, if, say, class X
only uses pointers or references to class Y, I will
write something like

class Y;
class X {
void f( Y *y );
const Y &g();
....
};However, if the class Y is nested, or defined
in a
namespace, this doesn't work. The obvious way to
do it:

class StockTable::Entry;
class A::C;
class Y {
void f( StockTable::Entry *e );
A::C *curr_ccc;
...
};

gives a compile error. Forward declaring "StockTable"

or "A" doesn't help. The only thing I have found that
works is including the full definition of StockTable,
which includes "Entry", and "A", which includes "C".

Primary Question:

Is it possible to forward declare Entry or C,
without including the definition of StockTable
or A?
Discussion Question:

Is there a good reason not to allow forward
declarations of the form "class A::C;"?

To me, it seems as ambiguous or unambiguous as
"class B;": it says that A::C is a class, which
will be defined within a scope "A".

Until defined, you can only declare pointers and
refs to it.

In order to do anything else, you need to define
"A" and "A::C" completely.

Or am I missing something?

Alan McKenney
[email]alan_mckenney1 (AT) yahoo (DOT) com[/email]

If so, how?

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Jonathan Mcdougall · Guest

Siemel Naran · Guest

Alan McKenney <alan_mckenney1 (AT) yahoo (DOT) com> wrote in message