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Syntax HELP

Started by julienX Jan 15, 2003 at 8:14 AM 1 reply 150+ views

Original Post

Jan 15, 2003 at 8:14 AM

Ok ill give an example to start with: MessageBox(NULL,"This is weird","Hello", MB_OK | MB_ICONINFORMATION); Why is only one | used? I''ve been taught in my book that to use the OR statement you would do it like this: if (choice1 || choice2) But in windows its all different, its always used once: only 1 | and only one &. Please, any advice would UNCONFUSE me!

Oh yeah, also why do you have to use the | to add multiple flags in windows? Wouldn''t you use & to say ''MB_OK AND MB_ICONINFORMATION, not ''MB_OK OR MB_ICONINFORMATION??

Miserable

Jan 15, 2003 at 8:19 AM

It is because | and || are entirely different operators (as are & and &&). || is a logical OR. | is a bitwise OR, used to combine the bits in two memory locations. Applied thus it works as expected: When at least once source bit is set, the destination bit will be set; if neither source bit is set, nor will be the target. (Bitwise AND works in an analogous fashion.)


  0100 1101
| 1001 1100
-----------
  1101 1101

Knowing this, the reason why you use the bitwise OR to combine bit flags should be fairly clear (it''s the only way to conveniently access individual bits).

julienX

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julienX

Jan 15, 2003 at 8:45 AM

Thanks a lot, I understand now

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