Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!samsung!umich!sharkey!bnlux0!max!drs
From: drs@max.bnl.gov (Dave Stampf)
Newsgroups: comp.sys.mac.programmer
Subject: Re: THINKC 4.0.2 #define is short
Keywords: #define preprocessor short int <<
Message-ID: <2312@bnlux0.bnl.gov>
Date: 14 Nov 90 18:02:13 GMT
References: <2374@moscom.UUCP>
Sender: news@bnlux0.bnl.gov
Reply-To: drs@max.UUCP (Dave Stampf)
Organization: Brookhaven National Lab, Upton NY
Lines: 39

In article <2374@moscom.UUCP> tcm@moscom.UUCP (Tom Maszerowski) writes:
>
>Here's a gotcha in THINK C 4.0.2 that got me.  It's probably in the
>manual somewhere, but a cursory galnce didn't reveal it ( I couldn't
>find any reference to #define or the preprocessor anywhere in the index).
>Anyway, this is what happened:
>
>given:
>
>#define   MaxAllocation  (1<<16)
>
>sets MaxAllocation to 0.  
>
>I believe that this is because the preprocessor assumes that
>MaxAllocation is an int ( 16 bits ) but the result of the shift is
>0x10000, which requires a long ( 32 bits ).  I realize that compiler
>implementers are free to make an int any size they want, but this is the
>first 68000 C compiler I've used where sizeof(int) != sizeof(long).  By

	The preprocessor assumes nothing. The word MaxAllocation is 
replaced as *text* everywhere with (1<<16). When you shift a 16 bit integer
16 places, you get 0. To get what you want, try 

#define MaxAllocation (1L<<16)

There are many compilers for 68000's and PC's which have sizeof(int) !=
sizeof(long). In fact, the reason for giving programmers the sizeof operator
is precisely to allow for varying architectures - get used to it. 

	By the way, I suspect that you will frequently run into the problem 
of Think C routines returning an int when you *know* that the routine returns
a something*. I have a note above my mac that says "int != char*". You may
want to do the same - it has saved me *hours* of debugging.

	< dave

(I agree however that it would be helpful if Symantec would describe the
operation of the preprocessor and perhaps even have a mode where you saw
that preprocessed text fed to the compiler (-E) option.)