Create data type

This is a discussion on Create data type within the C Programming forums, part of the General Programming Boards category; It's possible to create a data type, for example, a type named "bigint" with 8byte? With bit fields? Thanks for ...

  1. #1
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    Lightbulb Create data type

    It's possible to create a data type, for example, a type named "bigint" with 8byte? With bit fields?

    Thanks for answer.

  2. #2
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    Do you mean something like:
    Code:
    typedef long long bigint;

  3. #3
    ATH0 quzah's Avatar
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    Regarding bitfields:
    C: A Reference Manual, 5th Edition
    page 155, pharagraph 1:

    A bit field of n bits can represent unsigned integers in the range of 0 through 2^n-1 and
    signed integers in the range -2^n-1 through 2^n-1 -1, assuming a twos-complement represen-
    tation of signed integers. The origional definition of C permitted only bit fields of type un-
    signed
    , but Standard C permits bit fields to be of type unsigned int,
    signed int, or just int, termed unsigned, signed, and plain bit fields. Like plain char-
    acters, a plain bit field may be signed or unsigned. Some C implementations allow bit
    fields of any integer type including char. C99 allows bit fields of type _Bool.

    Page 156, pharagraph 2:

    Compilers are free to impose constraints on the maximum size of a bit field and
    specify certain addressing boundaries that bit fields cannot cross. These alignment restric-
    tions are usually related to the natural word size of the target computer. When a field is too
    long for the computer, the compiler will issue an appropriate error message. When a field
    would cross a word boundary, it may be moved to the next word.

    Page 197, footnote of Table 6-5:
    a Bit fields of type int, signed int, or unsigned int are assumed to have a conversion rank less than
    int, which means that their converted type depends on whether all their values can be represented in type int.
    While I don't have the standard around, and that's as much as relevant info I could find, I believe you cannot create a "new type" by simply specifying a larget value than the base type you're going from:
    Code:
    struct superhugenumber
    {
        unsigned x:1000;
    };
    It only makes sense. Otherwise, you could create nearly infinite numbers:
    Code:
    struct superhugenumber2
    {
        unsigned x:4000000000;
    }; /* four billion bits! */
    I assume, logicly, that you the number specified must fit in an int. So, on a 32 bit machine, we could specify a FOUR BILLION BIT bitfield. Do you really think that would work, or even that it realisticly should work? Not a chance.

    Quzah.
    Hope is the first step on the road to disappointment.

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