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From: beard@ux1.lbl.gov (Patrick C Beard)
Newsgroups: comp.sys.mac.programmer
Subject: Re: memTop, or how much RAM?
Message-ID: <4531@helios.ee.lbl.gov>
Date: 27 Dec 89 18:53:20 GMT
References: <6885@tank.uchicago.edu> <6886@tank.uchicago.edu>
Sender: usenet@helios.ee.lbl.gov
Reply-To: beard@ux1.lbl.gov (Patrick C Beard)
Organization: Lawrence Berkeley Laboratory, Berkeley
Lines: 26
X-Local-Date: 27 Dec 89 10:53:20 PST

In article <6886@tank.uchicago.edu> rfl@oddjob.uchicago.edu (Bob Loewenstein) writes:
>
>My last question may have been confusing..I need to know how much
>Ram is installed in the machine. Occasionally my application interprets
>a variable as pointer and before accessing memory perhaps pointed to, I 
>want to be sure that the "pointer" is pointing to a valid address.

Well, the safest thing to do would probably check that the pointer 
points to a valid address in your OWN heap, or the System heap, and all
other addresses aren't safe because they point to some other application's
heap.

However; you might for some reason wish to find out (if your were writing
a utility that does diagnostics or whatever) the extent of physical RAM.
I believe that the call MFTopMem gives you the address of the highest
useable byte in memory.

From the MPW interfaces:

pascal Ptr MFTopMem(void) = {0x3F3C,0x0016,0xA88F};

This is available on all systems beyond 6.0.
-------------------------------------------------------------------------------
-  Patrick Beard, Macintosh Programmer                        (beard@lbl.gov) -
-  Berkeley Systems, Inc.  ".......<dead air>.......Good day!" - Paul Harvey  -
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