Text 90, 55 rader
Skriven 2004-11-14 13:53:50 av Kurt Kuzba (1:261/38)
Ärende: [C] Enumerated Data Types in 'C'
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From: "Kurt Kuzba" <kkuzba@centurytel.net>


From: R. Scudder
RS>  The best way to learn how to use the language is to read good
RS>  code and see how more experienced people are doing things.
RS>  You will find many interesting and creative ways to use enum.

    I've hardly ever used it myself.  Once upon a time, I did use it
 for defining the basic 16 VGA colors for a colored text output
 function or two.  Something like this:

enum
  { Black,  Blue,  Green,  Cyan,  Red,  Magenta,  Yellow,  White,
   LBlack, LBlue, LGreen, LCyan, LRed, LMagenta, LYellow, LWhite};

 That was fairly practical, but I seldom used it, really, and after
 a while, I didn't use enum at all any more.  Are the enumerated
 variables inserted like macros when you compile in place of the
 labels?  I imagine that they are, but I have no real idea.
 I should try using enum in my mode 12h routines for bit masking on
 the bitplanes.  I'm using a static array now, and dereferencing of
 the values may be eating clock cycles I can save by using a set of
 enumerated values instead.  It's not much time, to be sure, but if
 you're writing hundreds of pixels, it adds up.  Here's what I'm
 using for bit value and bit mask now.

static int pix[8] = { 128,  64,  32,  16,   8,   4,   2,   1 };
static int pox[8] = { 127, 191, 223, 239, 247, 251, 253, 254 };

 The trouble is that I really don't see how to do it because the
 screen position only gives you a bit position 0-7, and I would
 still need to match the bit number to the bit and mask values
 for the & and | processes on each of the four bit planes.  As near
 as I can tell, enum wouldn't help me in a case like this, since
 there aren't any clear linear progressions involved.  If I were
 going the other way, like getting the day of the week from the day
 of the year, that would be different.

enum { Sunday, Monday, Tuesday, Wednesday,
       Thursday, Friday, Saturday };
enum { January, February, March, April, May, June,
       July, August, September, October, November, December };

 I can see how
   if(Saturday == day % 7)
 could be useful, though.  It makes the code more readable for when
 you go back and try to figure out what you did long, long, ago when
 you were still bright and cheerful instead of tired and grumpy.  :)

>  kkuzba@centurytel.net   http://home.centurytel.net/kkuzba
>  I am like an idiot, my mind is so empty.  (Tao te Ching #20)

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