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Using Bit fields

Posted on 2002-03-12
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Hi!
  I m back again with a another query , before that i must say God bless the team who thought of this site, has helped  me a lot during my studies, i m contributing my bit by recomending it to my friends.
  Getting back to my query, i want to  create a mask for a p'cular color in an image  , now i create this mask by creating a char array of the iamge size and using it for storing 1s for the corresponding color and 0s otherwise. This is not a problem , the problem is that just to store 1 bit data i m using 8bits(byte of a char) , i was suggested to use bit fields but then i cannot create an array of bitfield structure and since the image size varies i cannot predefine it. Please help

Anisha.
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Question by:Anisha
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ct.smith earned 400 total points
ID: 6859756
I suggest the STL container bitset.

SGI's reference has a good technical description:
http://www.sgi.com/tech/stl/bitset.html

Most (recent) C++ books should have good code examples of how to use the container.
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by:pjknibbs
ID: 6859876
If you want to do it the old-fashioned way you can just allocate your array at one-eighth the size you have it and use shift operations to read and set data--it would be quite easy to write functions to do this for you.

e.g. to set bit 370 in an array: array[370>>3] |= (1 << (370 & 7));
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Author Comment

by:Anisha
ID: 6859968
pjknibbs,
 thanks for the sugestion but i have kept that as an alternative, but i would  really wait and see if someone can help me with bitfields , life will be easier then.

Anisha.
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by:Axter
ID: 6861941
I agree with ct.smith.  You should use the bitset container.
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by:griessh
ID: 6955346
Dear Anisha

I think you forgot this question. I will ask Community Support to close it unless you finalize it within 7 days. You can always request to keep this question open. But remember, experts can only help you if you provide feedback to their questions.
Unless there is objection or further activity,  I will suggest to accept

     "ct.smith"

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If you think your question was not answered at all, you can post a request in Community support (please include this link) to refund your points. The link to the Community Support area is: http://www.experts-exchange.com/commspt/

PLEASE DO NOT ACCEPT THIS COMMENT AS AN ANSWER!
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Werner
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by:Mindphaser
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Force accepted

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