c++: external variables

[Newsnet Customer]

Hi,

Is an external variable a variable that is defined outside of a method? or a
variable with the extern modifier prefixed to it? and what's the difference
with external and global variables?


cheers
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[Buster Copley]

Re: external variables

Attila Feher wrote:[color=blue]
> Newsnet Customer wrote:
>[color=green]
>>Hi,
>>
>>Is an external variable a variable that is defined outside of a
>>method? or a variable with the extern modifier prefixed to it? and
>>what's the difference with external and global variables?[/color]
>
> [SNIP]
>
> The traditional definition of an external variable is a global variable,
> defined in another source (implementation ) file - brought into view by using
> an extern declaration.[/color]

I'm not sure. How about this: 'global' is a namespace. A variable
defined at namespace scope is available from any translation unit,
provided a declaration has been seen, and can therefore be loosely
described as a 'global variable' (unless the namespace is unnamed).
'external' is a storage class which describes any declaration at
namespace scope which is not also a definition. External declarations
are often necessary for 'global variables' because C++ has a
one-definition rule.
[color=blue]
> BTW, one really stupid question to anyone who has ever done something like
> this. How do you declare an extern variable, which is in a namespace? I
> never needed it yet, but this topic made me wonder. Is it this:
>
> namespace Whatever {
> extern int i;
> }
>
> ?[/color]

Yes. You can put that in a header. Then 'int Whatever::i;' or 'namespace
Whatever { int i; }' in one translation unit (with or without an
initializer).
[color=blue]
> --
> Attila aka WW[/color]