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From: phils@chaos.cs.brandeis.edu (Phil Shapiro)
Newsgroups: comp.sys.mac.programmer
Subject: Re: Think C Problem
Message-ID: <PHILS.90Nov19151704@chaos.cs.brandeis.edu>
Date: 19 Nov 90 20:17:04 GMT
References: <1990Oct27.074058.10748@agate.berkeley.edu>
	<4742@husc6.harvard.edu> <1990Nov18.070105.20735@agate.berkeley.edu>
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In-Reply-To: physi-hf@garnet.berkeley.edu's message of 18 Nov 90 07:01:05 GMT

In article <1990Nov18.070105.20735@agate.berkeley.edu> physi-hf@garnet.berkeley.edu (Howard Haruo Fukuda) writes:
   I'm not sure I understand your response.  My problem was that Think
   C was not putting my strings on word boundaries.  The line:

   Str255="\pHuh???";

   places the pascal string at an odd-numbered address (well, not neccessarily
   all the time).  For some reason changing the line to:

   static Str255="\pHuh???";

   does put the string on a word boundary.

   (Thanks to Steve Martin for telling about the above hack.)  Why
   does this work?

First, using "static" is not a solution, since globals may be odd
aligned in the same way that locals are.  Try:

main()
{
    static char c;
    static Str255 s;
}

and look at &c and &s in the debugger.

The fact is, Think C only word aligns your data if it is necessary.
The reason that Str255's do not necessarily have to be word aligned is
that all 680x0 machines allow odd address when accessing byte-sized
data.  That is, a "MOVE.B (Ax), xxx" will never fail.

So, if your strings are used for accessing characters you're all set.
If, however, you declare a Str255 and then cast it into an integer
pointer, you're asking for trouble.

The answer is (as Rich said) to make sure that your strings are word
aligned if you need it.  This can be accomplished by declaring an int
or long just before the string, or by always using NewPtr() to
allocate string storage.

The last time this came up, somebody mentioned some Toolbox routines
that expect word aligned strings (like SetIText?).  Does anybody have
a list?

	-phil
--
   Phil Shapiro                           Technical Support Analyst
   Language Products Group                     Symantec Corporation
		Internet: phils@chaos.cs.brandeis.edu