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From: beard@ux5.lbl.gov (Patrick C Beard)
Newsgroups: comp.sys.mac.programmer
Subject: Re: passing correct var size in MPW C/C++
Message-ID: <6280@helios.ee.lbl.gov>
Date: 25 Jul 90 19:26:49 GMT
References: <26ACA0CB.542F@wilbur.coyote.trw.com> <43315@apple.Apple.COM> <1990Jul24.235007.20545@laguna.ccsf.caltech.edu>
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Reply-To: beard@ux5.lbl.gov (Patrick C Beard)
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In article <1990Jul24.235007.20545@laguna.ccsf.caltech.edu> chi@tybalt.caltech.edu (Curt Hagenlocher) writes:
#In article <43315@apple.Apple.COM> marc@Apple.COM (Mark Dawson) writes:
#>I wrote a routine in assembly that I wanted to call from my C++ code, it
#>didn't end up working the way I expected--the C++ call kept passing a long,
#>when my assembly was expecting a short (2 bytes).  I've of course modifed
#>my assembly to expect a long, but I'd like to know where my thinking went
#>wrong.
#>
#
#MPW C always converts everything to 32 bits that's less than
#32 bits in length.  This includes characters and shorts.
#The information is put into the low (byte/word) and sign extended
#to make a long integer.

This is correct.  For all routines that use C calling conventions, all
types are pushed as 32-bit quantities.  One way to use smaller size parameters
is to declare a routine with "pascal" calling conventions.  So, if you
really only want to push a word, declare your routine as:

extern pascal void MyRoutine(short arg);

And C++, or C will only push a 2-byte integer on the stack.



--
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-  Patrick Beard, Macintosh Programmer                        (beard@lbl.gov) -
-  Berkeley Systems, Inc.  ".......<dead air>.......Good day!" - Paul Harvey  -
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