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From: chris@umcp-cs.UUCP
Newsgroups: net.lang.c
Subject: Re: sizeof "string"?  multi-line macro usage?
Message-ID: <2400@umcp-cs.UUCP>
Date: Sun, 13-Jul-86 21:04:00 EDT
Article-I.D.: umcp-cs.2400
Posted: Sun Jul 13 21:04:00 1986
Date-Received: Sun, 13-Jul-86 23:17:13 EDT
References: <343@vu-vlsi.UUCP>
Reply-To: chris@maryland.UUCP (Chris Torek)
Organization: University of Maryland, Dept. of Computer Sci.
Lines: 54

In article <343@vu-vlsi.UUCP> colin@vu-vlsi.UUCP (Colin Kelley) writes:
>Is it (portably) legal for sizeof to operate on a string constant?  I
>checked K&R, and they seem to have nothing to say about the subject.

K&R, by the inclusion of an explanatory sentence, made it ambiguous.
Appendix A, \S 7.1, Primary expressions, p. 186:

  A string is a primary expression.  Its type is originally ``array
  of char''; but following the same rule given above for identifiers,
  this is modified to ``pointer to char'' and the result is a pointer
  to the first character in the string.  (There is an exception in
  certain initializers; see \S 8.6.)

Had they left out the note about conversion to `pointer to char',
or had they mentioned sizeof in that last sentence, it would not
be ambiguous.  The ANSI draft standard simply declares a string
constant to have the type `array of char', making
`sizeof "foo the bar"' definitely equal to 12*sizeof(char).

>... This came up because I have coded
>
>#define PROMPT "prog> "
>
>in an include file, and then later used 
>
>for (i = 0; i < sizeof(PROMPT) - 1; i++) /* indent to first char of input */
>	putchar(' ');

There is another reason to avoid this: each time you mention the
string, most compilers generate another instance of it.  Using

>char prompt[] = PROMPT;

not only
>... _does_ work in Regulus
but also may keep your data space usage lower.

		* * *

>Does ANSI say anything about macro usage spanning more than one line?

The way I read the draft standard,

>#define max(a,b) ((a > b) ? a : b)
>
>x = min(very-long-expression-here,
>	another-very-long-expression-here);

is legal; but this is not explicit.  It depends on allowing `a
sequence of tokens' to include a newline.
-- 
In-Real-Life: Chris Torek, Univ of MD Comp Sci Dept (+1 301 454 1516)
UUCP:	seismo!umcp-cs!chris
CSNet:	chris@umcp-cs		ARPA:	chris@mimsy.umd.edu