Quick question...

This is a discussion on Quick question... within the C++ Programming forums, part of the General Programming Boards category; Is there a 1 bit varible type? And I'm not talking 1 byte (8 bit), like char....

  1. #1
    Registered User Queatrix's Avatar
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    Quick question...

    Is there a 1 bit varible type? And I'm not talking 1 byte (8 bit), like char.

  2. #2
    semi-colon generator ChaosEngine's Avatar
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    you can have a single bit in a struct or class as part of a bitfield
    Code:
    class bits
    {
        unsigned int b1 : 1;
        unsigned int b7 : 7;
    };
    note that using a single bit is actually much slower on most machines. why do you want this?
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    Just Lurking Dave_Sinkula's Avatar
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    Quote Originally Posted by Queatrix View Post
    Is there a 1 bit varible type? And I'm not talking 1 byte (8 bit), like char.
    Short answer: no.
    7. It is easier to write an incorrect program than understand a correct one.
    40. There are two ways to write error-free programs; only the third one works.*

  4. #4
    Registered User whiteflags's Avatar
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    The smallest addressable piece of memory is a byte. You aren't going to work around it incredibly easily: you could do something like what Chaos Engine showed you, but the other bits are going to be rationed off anyway whether they're used or not used.

  5. #5
    Registered User Queatrix's Avatar
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    The reason I was asking, is because I wanted to load a file into an array, that way, I can handle each binary bit with ease. Would Engine's solution work for this?

  6. #6
    and the hat of wrongness Salem's Avatar
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    > Would Engine's solution work for this?
    Nope.
    There is no way to determine whether unsigned int b1 : 1; is the MSB or LSB of a char, short or long.

    Bit fields are an internal representation only. You can't use them to access external devices, file formats, message streams etc in any meaningful way.
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    Reverse Engineer maxorator's Avatar
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    Read a byte and then cycle through its bits with bitwise operators.
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  8. #8
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    There's vector<bool> (specialized to use just 1 bit, not byte, per element) and bitset<N> (where N is known at compile time).

    Edit: http://www.thescripts.com/forum/thread60019.html
    Last edited by robatino; 05-29-2007 at 09:04 AM.

  9. #9
    Registered User Queatrix's Avatar
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    >> Read a byte and then cycle through its bits with bitwise operators.
    That is what I am currently doing, I was just hoping there was a better way.

    However, thanks for the responces all.

  10. #10
    pwns nooblars
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    Beware of vector<bool> it is not a normal/proper STL container, the algorithms that work on vectors are not guaranteed to work properly on vector<bool> since it is a specialized template. I ran into this problem before. Google a bit and become aware of the container you are using, since it isn't a traditional vector.

  11. #11
    Just Lurking Dave_Sinkula's Avatar
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    Quote Originally Posted by Queatrix View Post
    >> Read a byte and then cycle through its bits with bitwise operators.
    That is what I am currently doing, I was just hoping there was a better way.
    This is the same thing, only different:
    http://c-faq.com/misc/bitsets.html
    7. It is easier to write an incorrect program than understand a correct one.
    40. There are two ways to write error-free programs; only the third one works.*

  12. #12
    Woof, woof! zacs7's Avatar
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    So you wanted to read in from the file 'bit by bit'?

    eh...

  13. #13
    Registered User Queatrix's Avatar
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    @Zacs: Yup.
    @Dave: Like the link.
    @Wraithan: Okay, I figured I'm not going to use it anyway.
    Last edited by Queatrix; 05-30-2007 at 06:02 AM.

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