Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!romp!auschs!awdprime!woan.austin.ibm.com!ron
From: ron@woan.austin.ibm.com (Ronald S. Woan)
Newsgroups: comp.unix.aix
Subject: Re: Bogus warning from AIX XL C Compiler/6000?
Keywords: correct under ANSI definition
Message-ID: <3239@awdprime.UUCP>
Date: 23 Aug 90 15:56:52 GMT
References: <1990Aug23.034343.11444@murdoch.acc.Virginia.EDU>
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In article <1990Aug23.034343.11444@murdoch.acc.Virginia.EDU>,
mms7r@krebs.acc.Virginia.EDU (Mitch Smith) writes:
Mitch> Problem: The character constant in the following short program
Mitch> produces a bogus warning.
Mitch> /* test1.c */ main() { 	int c;
Mitch> 	c = '\x'; 	printf("c = %c\n", c); 	exit(0); }
Mitch> ..............a..  a - 1506-235: (W) Illegal escape sequence x
Mitch> ignored.  $

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

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

Yes, get the new ANSI edition of K&R. On page 193: "If the character
following the \ is not one of those specified, the behavior is
undefined." And actually, 'x' just happens to have been defined for
specifying constants in hex, i.e. '\x07' is the bell. You should thank
your lucky stars that you got the right output or the fact that IBM
has tried to be as backwards compatible as possible, so they only gave
you a very good warning message with an indication of what it was
going to do with it. Anyway, this doesn't seem like something you
should be trying to do anyway, afterall what's wrong with c='x'?

					Ron

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