> On Sun, Aug 17, 2014 at 4:38 AM, Ruben J=F6nsson <ruben@rjjournal.net> wr=
ote: >
> Have you considered using a union for that: > > union { >   uint32_t rgb_=
32; > =20
> struct { >     uint8_t red:8; >     uint8_t green:8; >     unit8_t blue:8=
; > =20
> }col; > }rgb; > > This way you can access the 32 bit value with rgb.rgb_3=
2 and,
> for > example red with rgb.col.red for both reading and writing. > > You =
can
> still use the shift/multiply methods with rgb.rgb_32 (but you > need to k=
now how
> the bitfields are ordered by the compiler). > > The union means that the
> variables within it shares the same memory > (rgb_32 and col in this case=
).
>=20
> Hi Ruben,
>=20
> Actually, this was going to be my next step! I wanted to make sure I
> could send enough data to get control of the LEDs first, before I
> started playing with different memory structures.
>=20
> Since you've raised it, one of the things that's always confused me
> about unions is in the declaration process. For instance, take your
> code snippet above. I understand the parts, though I'm unsure about
> the "rgb" at the end. Is that defining the new datatype, that I could
> then use to declare variables? For your following code, would I have
> had to declare "rgb rgb;" first?
>=20
> Further, since I'm using these LEDs in a string, I'm storing their
> values in an array. Could I then just declare an array like this: rgb
> led_colors[8]; (as an example)?
>=20
> Thanks!
>=20
> Josh

Well actually it could be something like this instead:

typedef union {
  uint32_t rgb_32;
  struct {
    uint8_t red:8;
    uint8_t green:8;
    uint8_t blue:8;
    uint8_t pad:8;
  }col;
}RGB;

Then you can do:

RGB rgb;
rgb.col.red=3D12;

An array would also be fine:

RGB rgb[10];
rgb[5].col.red=3D12;

If you don't have the typedef you need to explicitly declare it as:

union RGB rgb;

/Ruben

=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D
Ruben J=F6nsson
AB Liros Electronic
Box 9124, 200 39 Malm=F6, Sweden
TEL INT +46 40142078
FAX INT +46 40947388
ruben@pp.sbbs.se
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D

--=20
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