andrew@resam.dk (Leif Andrew Rump) (01/19/91)
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
> > Read oe as: o <backspace> / (slash) and OE as O <backspace> / (slash) < <diamond@jit345.swstokyo.dec.com (Norman Diamond) (01/19/91)
In article <1991Jan18.170921.4866@resam.dk> andrew@resam.dk (Leif Andrew Rump) writes: >#define FOLDER fk >#ifdef FOLDER > part 1 >#endif >#if FOLDER == fk > part 2 >#endif > >It worked OK for part 1 ... but part 2 get compiled under any circumstances > >#ifdef FOLDER == CASE > part 2 >#endif > >So this rules out that the presence is equal 1 and absence equal 0! Absence equals zero, yes. Presence equals whatever the defined value is. Now let's see what happens when you test #if FOLDER == fk #if fk == fk #if 0 == fk #if 0 == 0 which is true. #ifdef FOLDER == CASE is syntactically invalid. Assume you meant #if and let's see: #if FOLDER == CASE #if 0 == CASE #if 0 == 0 If you want a macro to evaluate to something other than 0, you must give it a value (a replacement-list) that evaluates as a constant-expression. Doug Gwyn already posted correct examples. -- Norman Diamond diamond@tkov50.enet.dec.com If this were the company's opinion, I wouldn't be allowed to post it.