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Re: QUERRY about two-character punctuation tokens, called di
Joined: 29 Dec 2004
Posts: 31
Re: QUERRY about two-character punctuation tokens, called di
From: Ashish Gupta [mailto:ashish_gupta_cal@...]
>Hi,
> C++ also recognizes two-character punctuation
>tokens, called digraphs. The digraphs and their
>equivalent tokens are:
>
> <: [
> :> ]
> <% {
> %> }
> %: #
> %:%: ##
These are actually called punctuators in ISO/IEC 9899:1999 (it uses the
term digraph in "quotes" in a footnote).
There also exist trigraphs:
??= #
??( [
??/
??) ]
??` ^
??< {
??! |
??> }
??- ~
>The following program is valid in both C99 and C++:
[snip]
> My question is what is the need of such digraphs?
Because while ISO/IEC 9899:1999 requires that (among others) the
following characters `exist` in the "source character set" and
"execution character set":
! " # % & ` ( ) * + , - . / :
; < = > ? [ ] ^ _ { | } ~
some character sets don`t acutally have them. `Digraphs` and trigraphs
allow the use of the above required characters without actually using
them.
For example ISO/IEC646 (Information technology - ISO 7-bit coded
character set for information
interchange) which is quoted in 8988:1999 as a reference [1] doesn`t
actually have a # character
Of course, in general these days, the only use digraphs and trigraphs
have is in obfuscation - at least that`s the only use I`ve found for
them.
[1] <http://www.kostis.net/charsets/iso646.gb.htm>
--
PJH
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Joined: 24 Jan 2005
Posts: 2
Re: QUERRY about two-character punctuation tokens, called di
Thanks ,
your reply was very clear and it cleared my
doubt.
Regards
Ashish.
--- Paul Herring <pherring@...> wrote:
>
> From: Ashish Gupta
> [mailto:ashish_gupta_cal@...]
>
> >Hi,
> > C++ also recognizes two-character punctuation
> >tokens, called digraphs. The digraphs and their
> >equivalent tokens are:
> >
> > <: [
> > :> ]
> > <% {
> > %> }
> > %: #
> > %:%: ##
>
> These are actually called punctuators in ISO/IEC
> 9899:1999 (it uses the
> term digraph in "quotes" in a footnote).
>
> There also exist trigraphs:
>
> ??= #
> ??( [
> ??/
> ??) ]
> ??` ^
> ??< {
> ??! |
> ??> }
> ??- ~
>
>
> >The following program is valid in both C99 and C++:
>
> [snip]
>
> > My question is what is the need of such
> digraphs?
>
> Because while ISO/IEC 9899:1999 requires that (among
> others) the
> following characters `exist` in the "source
> character set" and
> "execution character set":
>
> ! " # % & ` ( ) * + , - . / :
>
> ; < = > ? [ ] ^ _ { | } ~
>
> some character sets don`t acutally have them.
> `Digraphs` and trigraphs
> allow the use of the above required characters
> without actually using
> them.
>
> For example ISO/IEC646 (Information technology - ISO
> 7-bit coded
> character set for information
> interchange) which is quoted in 8988:1999 as a
> reference [1] doesn`t
> actually have a # character
>
> Of course, in general these days, the only use
> digraphs and trigraphs
> have is in obfuscation - at least that`s the only
> use I`ve found for
> them.
>
>
> [1] <http://www.kostis.net/charsets/iso646.gb.htm>
>
> --
> PJH
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