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From: drw@cullvax.UUCP (Dale Worley)
Newsgroups: comp.lang.c
Subject: assert
Message-ID: <936@cullvax.UUCP>
Date: Wed, 18-Mar-87 17:41:18 EST
Article-I.D.: cullvax.936
Posted: Wed Mar 18 17:41:18 1987
Date-Received: Fri, 20-Mar-87 02:18:02 EST
Organization: Cullinet Software, Inc., Westwood, MA
Lines: 37

Dizio@udel.edu writes:
> I found this macro for assert in <assert.h> under ULTRIX 1.2
> under the SYSTEM_FIVE #ifdef
> 
> #define assert(EX) if (EX) ; else _assert("EX", __FILE__, __LINE__)
>                                           ^culprit
> 
> It fails when given given an expression containing '"'.  
>   eg. assert ((fp = fopen("filename","r")) != NULL)
> 
> I realize this is a minor point as I could simply write my own macro,
> but I just wondered if the proposed standard has specified whether
> any valid expression should be able to be used inside the assert,
> Or only expressions which don't contain '"'.

The standard requires that assert() work for any expression.  But, if
you want to write your own assert(), you can do things like

#define	assert(EX)	( (EX) ? _assert(#EX, __FILE__, __LINE__)

ANSI C won't let you substitute parameters inside quoted strings, but
it will let you convert a parameter into a string literal via #.  # is
also required to handle things containing "s correctly.  E.g.,

	#define stringify(EX)	#EX
	stringify(printf("Foo\n"))

yields

	"printf(\"Foo\\n\")"

Dale
-- 
Dale Worley		Cullinet Software
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