about meta character and character coding .

about meta character and character coding .

[waterloo]

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I can not understand the following para in Emacs Lisp Reference :

In a string, the 2**7 bit attached to an ASCII character indicates a
> meta character; thus, the meta characters that can fit in a string have
> codes in the range from 128 to 255, and are the meta versions of the
> ordinary ASCII characters.  (In Emacs versions 18 and older, this
> convention was used for characters outside of strings as well.)


One bit has two states.
Does 2**7 bit denote 7 bits ?

What does `thus, the meta characters that can fit in a string have
codes in the range from 128 to 255, and are the meta versions of the
ordinary ASCII characters. ' mean ?

Thanks

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Re: about meta character and character coding .

[Colin S. Miller]

waterloo wrote:
> I can not understand the following para in Emacs Lisp Reference :
> 
>     In a string, the 2**7 bit attached to an ASCII character indicates a
>     meta character; thus, the meta characters that can fit in a string have
>     codes in the range from 128 to 255, and are the meta versions of the
>     ordinary ASCII characters.  (In Emacs versions 18 and older, this
>     convention was used for characters outside of strings as well.)
> 
> 
> One bit has two states.
> Does 2**7 bit denote 7 bits ?
It means the 7th bit (counting from 0),
which has the value 128, or 2 to the power of 7.
(the caret character, which is sometime used to represent powerof,
also means the bitwise-or operation in the C programming language).

> 
> What does `thus, the meta characters that can fit in a string have
> codes in the range from 128 to 255, and are the meta versions of the
> ordinary ASCII characters. ' mean ?
It means the character A has value 65, and meta-A has the value 193,
being 128+65.

> Thanks

HTH,
Colin S. Miller


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