[erlang-questions] Bit syntax decscription in erlang reference manual?

成立涛 <>
Fri Jun 20 11:27:41 CEST 2008


thank you! :)

2008/6/20 Edwin Fine <>:

> Sounds right to me.
>
> One little thing, though: the newer versions of Erlang support a type,
> "bytes", which is identical to binary, but a more accurate description.
> There is also a size_bytes() function. As I understand it, we are encouraged
> to phase out the use of binary in favor of bytes.
>
> So the example could have been written with a more "modern" syntax as:
>
> <<A:1/bytes,B/bytes>> = <<1,2,3>>.
> S = byte_size(B).
>
> Example:
> 10> <<A:1/bytes,B/bytes>> = <<1,2,3>>.
> <<1,2,3>>
> 11> S = byte_size(B).
> 2
> 12> A.
> <<1>>
> 13> B.
> <<2,3>>
>
> Hope this helps.
>
>
> On Fri, Jun 20, 2008 at 12:00 AM, 成立涛 <> wrote:
>
>> yeah. I see. Thank you very much Edwin.
>> my opinion: in binary syntax, the integer, float can always use their
>> default size, but binary(bits and bytes) must declare its size specification
>> except the very last binary element. Is't  right?
>> I come from china, so my english is not good, please don't mind my
>> expression. :)
>>
>> 2008/6/20 Edwin Fine <>:
>>
>> There's a subtlety here that you may have missed. The manual says
>>>
>>> All other *bit string or binary* elements in the matching must have a
>>> size specification.
>>>
>>> In <<A, B, C>> = <<1,2,3>>, all elements on the left hand side are by
>>> default of type integer, not bitstring or binary. Therefore sizes are
>>> assumed to be 1 byte each.
>>>
>>> Your example is the same as writing
>>>
>>> <<A/integer, B/integer, C/integer>> = <<1,2,3>>.
>>>
>>> This below, for example, would NOT work:
>>>
>>> <<A/binary,B/binary>> = <<1,2,3>>.
>>>
>>> You would have to write
>>>
>>> <<A:1/binary,B/binary>> = <<1,2,3>>.
>>>
>>> Example:
>>> 1> <<A/binary,B/binary>> = <<1,2,3>>.
>>> * 1: a binary field without size is only allowed at the end of a binary
>>> pattern
>>> 2> <<A:1/binary,B/binary>> = <<1,2,3>>.
>>> <<1,2,3>>
>>> 3> A.
>>> <<1>>
>>> 4> B.
>>> <<2,3>>
>>> 5>
>>>
>>> Hope this helps.
>>> 2008/6/19 成立涛 <>:
>>>
>>>> In erlang reference mannual, the Bit Syntax Expressions section, about
>>>> the binary Size, the manual said:
>>>> "In matching, this default value is only valid for the very last
>>>> element. All other bit string or binary elements in the matching must have a
>>>> size specification."
>>>> we know the default size for integer is 8, float is 64, binary is the
>>>> whole bytes.
>>>> for example:
>>>> > <<A, B, C>> = <<1, 2, 3>>.
>>>> I think in this pattern match, the variables A, B, C all use the dafault
>>>> Size.
>>>> Is it a conflict with reference manual?
>>>> thanks!
>>>>
>>>> _______________________________________________
>>>> erlang-questions mailing list
>>>> 
>>>> http://www.erlang.org/mailman/listinfo/erlang-questions
>>>>
>>>
>>>
>>
>
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