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From: Patrick Scheible <kkt@zipcon.net>
Newsgroups: comp.lang.c
Subject: Re: trigraphs, yecch
References: <4f2808f4.648026530@text.giganews.com> <ln4nvbxxkb.fsf@nuthaus.mib.org>
Date: Tue, 31 Jan 2012 17:01:18 -0800
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Keith Thompson <kst-u@mib.org> writes:

> cri@tiac.net (Richard Harter) writes:
>> The other day I wanted to put three successive question marks in a
>> string.  Frex, "(???).%s.%s".  My trusty antique gcc compiler
>> converted the last two '?'s into a ']' along with a warning that it
>> was doing a trigraph conversion.
>>
>> Now, me, I know from nothing about trigraphs - never used them, hope
>> never to use them - so I was caught by surprise.  My elderly copy of
>> K&R described them but I didn't see anything about getting around
>> them.
>>
>> So.  How is one supposed to get three successive question marks into a
>> string?
>
> For reference, there are exactly 9 trigraphs.  C99 5.2.1.1:
>
>     All occurrences in a source file of the following sequences of three
>     characters (called trigraph sequences) are replaced with the
>     corresponding single character.
>
>         ??= #     ??) ]    ??! |
>         ??( [     ??' ^    ??> }
>         ??/ \     ??< {    ??- ~
>
>     No other trigraph sequences exist. Each ? that does not begin one of
>     the trigraphs listed above is not changed.
>
> In your case, "???" is not a trigraph, but ??) is.

Has the C standards committee been flamed enough for trigraphs?  I don't
think so.  I bet there's 1000 programmers bitten by them for every 1
who's been helped.  By 1989 anyone who didn't have an editor capable of
typing any 7-bit ASCII character was a hopeless luddite who would be
better served making their own pre-preprocessing phase for C and leaving
the language unchanged instead of another phase in the preprocessor for
every C program forever and ever.

-- Patrick