On 6/10/2013 10:55 AM, Manu Abraham wrote:
> On Mon, Jun 10, 2013 at 8:07 PM, Joe Wronski <jwronski@stillwatereng.net>=
 wrote:
>> On 6/10/2013 10:03 AM, Manu Abraham wrote:
>>> One thing that I don't understand is, why he does this: " static
>>> uint8_t old_AB =3D 0;" that would loose the previous state altogether,
>>> wouldn't it ?
>> No, the "=3D0" is only assigned when the static old_AB is allocated and
>> initialized, after that, it retains it's value as set by the "old_AB =3D=
"
>> assignments in read_encoder()
>
> Please note the next line:
>
>
>    static uint8_t old_AB =3D 0;
>    /**/
>    old_AB <<=3D 2;                   //remember previous state
>
> Once you initialize the variable to 0, then there is no way that it
> can remember
> the previous state.
>
I can't find my K&R book right now, but this should clear that idea up:

<http://en.wikipedia.org/wiki/Static_variable>

In func() there is this line:

static  int  x=3D  0;  // x is initialized only once across three calls of =
func()

Joe W


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