forward declaration of class in namespace

[flopbucket]

Hi,

How can I forward declare a class that is in a different namespace? As
a simple example:

classs Foo
{
std::string *string;
};
With other classes, I could always "class Y;" at the top to forward
declare, but how can I forward declare std::string? Is it possible?

I tried

class std::string;

but that did not work.

Any information appreciated.

Thansk

[Ian Collins]

flopbucket wrote:

Hi,

How can I forward declare a class that is in a different namespace? As
a simple example:

classs Foo
{
std::string *string;
};
With other classes, I could always "class Y;" at the top to forward
declare, but how can I forward declare std::string? Is it possible?

I tried

class std::string;

but that did not work.

You probably can't for std:: string because it is a typedef, not a class.

If you want to forward declare a class from a namespace, use

namespace someNamespace
{
SomeClass;
}

--
Ian Collins.

[Mark P]

Ian Collins wrote:

flopbucket wrote:

Hi,

How can I forward declare a class that is in a different namespace? As
a simple example:

classs Foo
{
std::string *string;
};
With other classes, I could always "class Y;" at the top to forward
declare, but how can I forward declare std::string? Is it possible?

I tried

class std::string;

but that did not work.

You probably can't for std:: string because it is a typedef, not a class.

If you want to forward declare a class from a namespace, use

namespace someNamespace
{
SomeClass;
}

That works in general, however IIRC it's not allowed to put anything in
namespace std so there's no way to forward declare names from std
(except where explicitly provided, e.g. <iosfwd>).