trigraphs ????

trigraphs ????

[Aparna Ranish]

Hi
         Can somebody tell me what is the usage of trigraphs ??? Is it supported by all the Compilers.
                                   
Thanx and regards
Aparna Ranish

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Re: trigraphs ????

[Michael Meissner]

On Thu, Jul 05, 2001 at 07:15:53AM -0000, Aparna  Ranish wrote:
> Hi
> Can somebody tell me what is the usage of trigraphs ??? Is it supported by
> all the Compilers.

It is required to be supported by all ISO standard compilers.  The usage of
trigraphs is to work around problems where some characters in the C source
character set aren't available in the local character set (ie, some varients of
ISO 646 in other countries use the same byte value for curley braces and other
characters).

-- 
Michael Meissner, Red Hat, Inc.  (GCC group)
PMB 198, 174 Littleton Road #3, Westford, Massachusetts 01886, USA
Work:	  meissner@redhat.com		phone: +1 978-486-9304
Non-work: meissner@spectacle-pond.org	fax:   +1 978-692-4482

Re: trigraphs ????

[Zack Weinberg]

On Thu, Jul 05, 2001 at 12:39:57PM -0400, Michael Meissner wrote:
> On Thu, Jul 05, 2001 at 07:15:53AM -0000, Aparna  Ranish wrote:
> > Hi
> > Can somebody tell me what is the usage of trigraphs ??? Is it supported by
> > all the Compilers.
> 
> It is required to be supported by all ISO standard compilers.  The
> usage of trigraphs is to work around problems where some characters
> in the C source character set aren't available in the local
> character set (ie, some varients of ISO 646 in other countries use
> the same byte value for curley braces and other characters).

However, note that trigraphs are disabled by default in GNU C/C++/ObjC.
To enable them, you must use a command line switch: any of -trigraphs,
-ansi, -std=c89, -std=c99, -std=c++98 will do the trick.  The latter
four have other effects as well.

-- 
zw   You have to care about the 'fair trial' part; you have to care about
     the 'due process of law' part, and you have to care about these things
     *more* than you care about putting child molestors away.
     	-- Graydon Saunders

Re: trigraphs ????

[Yann Collete]

Hello,

trigraphs are symbols composed with three chars and beginning with the
two following chars ::. These symbols are converted into a char. For example

::) -> ]
::( -> [
etc..

(I'm not sure of the correspondance between trigraphs and chars).
Now, I've got a question:

Is trigraphs used for something ????

YC

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> 
> Hi
>          Can somebody tell me what is the usage of trigraphs ??? Is it 
supported by all the Compilers.
>                                    
> Thanx and regards
> Aparna Ranish
> 
> ____________________________________________________
> Buy Feng Shui Package for Rs. 151/- only, at 
http://shopping.rediff.com/shopping/fengshui_mailer.htm
> 
> 
> 

Re: trigraphs ????

[Ingo Krabbe]

>
> Is trigraphs used for something ????
>
I think they have been used for something but are not very usefull in our
days. Trigrpahs should achieve extending some charactersets which don't
have some characters. Anyway there has to be some reason why ISO once has
introduced these sequences.

Excerpt from gcc manual:
=================================== snip
       -trigraphs
           Process ISO standard trigraph sequences.  These are
           three-character sequences, all starting with ??, that
           are defined by ISO C to stand for single characters.
           For example, ??/ stands for \, so '??/n' is a charac-
           ter constant for a newline.  By default, GCC ignores
           trigraphs, but in standard-conforming modes it con-
           verts them.  See the -std and -ansi options.

           The nine trigraph sequences are

           ??( -> [

           ??) -> ]

           ??< -> {

           ??> -> }

           ??= -> #

           ??/ -> \

           ??' -> ^

           ??! -> |

           ??- -> ~

           Trigraph support is not popular, so many compilers do
           not implement it properly.  Portable code should not
           rely on trigraphs being either converted or ignored.

=================================== snip