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From: andrew@resam.dk (Leif Andrew Rump)
Newsgroups: comp.lang.c,comp.std.c
Subject: Is it only ANSI C that allow #if to compare symbols?
Keywords: sun C #if
Message-ID: <1991Jan18.170921.4866@resam.dk>
Date: 18 Jan 91 17:09:21 GMT
Distribution: comp
Organization: RESAM Project Office, SAS, CPHML-V
Lines: 41

Hello netters - please help me with this one - this will be the last one -
and if you believe that then I have an Eiffeltower to sell you!!!  :-)

I tried this construction on our Sun C compiler (please no flames!):

#define	FOLDER	fk
...
#ifdef	FOLDER
  part 1
#endif
...
#if	FOLDER == fk
  part 2
#endif

It worked OK for part 1 i.e. if FOLDER is defined (never mind it's
value) then part 1 if compiled but part 2 get compiled under any
circumstances _even_ if you only define one of two symbols and write:

#ifdef	FOLDER == CASE
  part 2
#endif

So this rules out that the presence is equal 1 and absence equal 0!
The manual states "#if constant-expression ... All binary non-assign=
ment C operators, including '&&', '||' and ',', are legal ... The '?:'
operator, and the unary '-', '!', and '~' operators, are also  ..."

Is there any other way I may check a symbols value?

Any suggestions?

Leif Andrew

Leif Andrew Rump, AmbraSoft A/S, Stroedamvej 50, DK-2100 Copenhagen OE, Denmark
UUCP: andrew@ambra.dk, phone: +45 39 27 11 77                /
Currently at Scandinavian Airline Systems                =======/
UUCP: andrew@resam.dk, phone: +45 32 32 51 54                \
SAS, RESAM Project Office, CPHML-V, P.O.BOX 150, DK-2770 Kastrup, Denmark

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