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From: mms7r@krebs.acc.Virginia.EDU (Mitch Smith)
Newsgroups: comp.unix.aix
Subject: Bogus warning from AIX XL C Compiler/6000?
Message-ID: <1990Aug23.034343.11444@murdoch.acc.Virginia.EDU>
Date: 23 Aug 90 03:43:43 GMT
Sender: news@murdoch.acc.Virginia.EDU
Organization: University of Virginia
Lines: 50

System:  RS/6000 Model 530
         AIX 3.1
         AIX XL C Compiler/6000

Problem:
         The character constant in the following short program
	 produces a bogus warning.

/* test1.c */
main()
{
	int c;

	c = '\x';
	printf("c = %c\n", c);
	exit(0);
}

         The output of the compiler invoked as "cc" is as follows:

$ make test1
        cc -O  test1.c -o test1
        5 |         c = '\x';
            ..............a..
a - 1506-235: (W) Illegal escape sequence x ignored.
$

	In fact, 'x' is not ignored.  When executed, the
	compiled program prints "c = x".

	The program above compiles without errors or warnings
	on an AT&T 3B15, an SGI IRIS 3030, a MicroVAXII BSD4.3,
	a MIPS M/120, an SGI IRIS 4D/310, and an IBM-PC with
	Microsoft C 5.1.

	According to K&R (1978), page 181, under the section on
	character constants:  "If the character following a
	backslash is not one of those specified, the backslash is
	ignored."  [The "specified" escape sequences being '\n',
	'\t', etc.]

	Thus, the escape sequence should not be illegal, and if the
	warning message is going to print anything it should be
	the backslash that should be ignored. Has this behavior
	been outlawed by a recent Standard?

Mitch Smith
Department of Microbiology	mms7r@virginia.edu
University of Virginia		...!{uunet,mcnc}!virginia!mms7r
Charlottesville, VA 22908	(804) 924-2669