Checksum: 33476
Lines: 48
Path: utzoo!sq!msb
From: msb@sq.com (Mark Brader)
Date: Mon, 13-Mar-89 20:31:40 EST
Message-ID: <1989Mar13.203140.5054@sq.com>
Newsgroups: comp.lang.c
Subject: Re: Max line length (was Re: programming challenge ...)
References: <2102@jasper.UUCP> <207600017@s.cs.uiuc.edu> <9777@bloom-beacon.MIT.EDU>
Reply-To: msb@sq.com (Mark Brader)
Organization: SoftQuad Inc., Toronto

> What is the longest line allowed in a C program?  Does the standard say?
> Do present compilers care?

It's still a proposed standard, technically.  X3 has accepted it,
so it will be becomes a standard, but it hasn't actually been
officially called one yet.

#  2.2.4.1  Translation Limits
#     The implementation shall be able to translate and execute at least
#  one program that contains at least one instance of every one of the
#  following limits*:
#
#     ...
#     509 characters in a logical source line
#  ...

#  *An implementation should avoid imposing fixed translation limits
#  wherever possible.

"Logical" source line is defined in 2.1.1.2 as what you get after you
(notionally, at least) replace your system's idea of end-of-line with
UNIX-like newline characters, translate trigraphs into the corresponding
characters, and then eliminate any backslash-newlines.

By the way, any nonempty source file is required to end with an
unbackslashed newline.  Of course, a compiler is at liberty to ignore
this requirement.

Now I suppose I should describe trigraphs, to forestall any followups from
new readers.  C was designed to use almost the full ASCII character set,
which causes problems in Europe where the bit patterns that ASCII uses for
things like # and \ and { are instead used for accented letters (different
ones in different countries, yet), and so, many terminals lack those
characters altogether.  As a partial workaround for this problem -- and
nobody pretends it is more than that -- an ANSI C compiler is required to
recognize in its initial translation phase the sequences ??= ??( ??/ ??)
??' ??< ??! ??> ??- (called trigraphs) and replace them respectively with
the characters # [ \ ] ^ { | } ~ which are needed for C but may not be
available in some character sets.  Please DO NOT post suggestions for
alternatives to the net; all possibilities have been discussed AT LENGTH.

The sed command in my signature below is to fix any old programs that may
have accidentally contained trigraphs (the only likely case would be
printf ("What??!\n");) by inserting a backslash between the ?'s to break
up the trigraph without changing the string.  ('\?' == '?' in ANSI C.)

Mark Brader, Toronto		sed -e "s;??\\([-=(/)'<!>]\\);?\\\\?\\1;g"
utzoo!sq!msb, msb@sq.com	will fix them...	-- Karl Heuer