On Tue, Sep 06, 2005 at 03:13:48PM -0400, Robert P. J. Day wrote:
>
> i'm looking at some legacy code and, in a header file, i find the
> following (paraphrased for brevity):
>
> typedef struct {
> ... stuff ...
> } Widgets ;
>
> extern Widgets Widget ;
>
>
> huh? i can see why a header file would want to define a structure
> but i'm confused why the *header* file would then refer to an external
> object of that type. that's a new one on me -- typically, i'd expect
> a *source* file to define such a thing and other *source* files to
> contain the "extern" declaration.
>
> is this some subtle programming cleverness of which i am unaware?
> thanks.
>
This is done quite frequently when a data structure needs to be referenced from
multiple locations. They're not necessicarily consecutive like that, but its
rather a common practice to extern a instance of a type in a header file. The
kernel source tree does this very frequently, check include/net/ipv4 for lots of
examples.
Regards
Neil
> rday
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