The first struct is anonymous but its sub-fields are not. The second
struct is also anonymous but its only field is anonymous also, so you
don't have a means to reference it.

You must give a name to the bit-field. Better, you could also use a
'char' field instead of the second struct.

One more point, 'unsigned' is a 16-bit type, if you want your union to
occupy just one byte, declare the fields as 'unsigned char'.


Isaac


On 18/03/2015 21:24, Josh Koffman wrote:
> Hi all,
>
> I'm trying to define a status register in XC8. I'd like to be able to
> reference individual bits, but also be able to say, clear the variable
> as a whole.
>
> I currently have it defined as this:
>
> typedef union {
>         struct
>         {
>             unsigned ENC1UP                    :1;
>             unsigned ENC1DN                    :1;
>             unsigned ENC2UP                    :1;
>             unsigned ENC2DN                    :1;
>             unsigned ENC3UP                    :1;
>             unsigned ENC3DN                    :1;
>             unsigned ENC4UP                    :1;
>             unsigned ENC4DN                    :1;
>         };
>         struct
>         {
>             unsigned                            :8;
>         };
>
> } EncStatus_t;
>
> In another part of the code, I define a variable using the typedef EncSta=
tus_t.
>
> In my code, I have two lines that try to write to that variable:
>
>    EncStatus.ENC1DN =3D 1;
>    EncStatus =3D 0;                  // Clear encoder status register
>
> The first line works perfect. The second line throws an error though -
> illegal conversion between types - int -> volatile union.
>
> I understand the basic problem here, but I can't seem to fix it. I've
> spent a bunch of time looking at the header file for my processor, to
> see how I can write to both PORTB and PORTBbits.RB0 successfully. Near
> as I can tell, it's because both of those variables are explicitly
> being declared at the same address, not because there's anything fancy
> in the union.
>
> So...is there a way to deal with this when I don't know where the
> variable will be assigned?
>
> To be clear, this isn't a work stopping problem, I'd just like to know
> if there's a way to do this that is efficient. After all, I can always
> just clear each bit individually.
>
> Thanks!
>
> Josh

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