Hi Josh, the extern is a declaration, telling the compiler that the=20
variable will be defined somewhere else in the project.  The point being=20
that you can then use it in your code in that .c file or in numerous .c=20
files.

But, you have to define it somewhere, and only once:
volatile uint32_t millicnt;

so that millicnt actually exists.  Typically you'd do this in whatever=20
..c file has your main().

<http://www.cprogramming.com/declare_vs_define.html>

The linker is complaining that you haven't defined it.

In other news, I found another XC8 compiler bug today!

J



Josh Koffman wrote:
> Hi all,
>
> I am pretty sure I'm doing something wrong here. Several hours of
> trying to figure out why has proven fruitless, so I need some help
> clearly.
>
> I have a header file. In it, I declare a variable like this:
>
>    extern volatile uint32_t millicnt;   // Counter for milliseconds
>
> That header file is #included at the top of my main project file. It
> is also included at the top of its corresponding .c file. However, if
> I try to use the variable millicnt in either of those two files, I get
> a linker error about an undefined symbol. This is a linker error, not
> a compiler error:
>
> :0: error: (499) undefined symbol:
>          _millicnt(dist/default/production/LED_Faceplate_v1.production.ob=
j)
> (908) exit status =3D 1
>
> Try as I might, I can't seem to puzzle this one out. There is a
> typedef right above the variable declaration that does appear to work
> in other files, so I'm a bit stumped here. I could just move the
> declaration to another file and it would work, but this seems like a
> bit of cheating.
>
> Any thoughts?
>
> Thanks!
>
> Josh
>
--=20
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