Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!tut.cis.ohio-state.edu!cwjcc!hal!nic.MR.NET!eta!com50!pwcs!stag!dynasoft!john
From: dynasoft!john@stag.UUCP (John Stanley)
Newsgroups: comp.sys.atari.st
Subject: Re: nullfilling
Message-ID: <0217890118120601@dynasoft.UUCP>
Date: 17 Mar 89 06:18:12 GMT
Reply-To: dynasoft!john@stag.UUCP (John Stanley)
Organization: DynaSoft Systems, Minneapolis, MN.
Lines: 29
X-Member-Of: STdNET (ST Developer's Network)

[danw@tekchips.LABS.TEK.COM (Daniel E. Wilson) writes...]

>   K&R say nothing about clearing memory.  Only static variables are
> cleared and this is done by the compiler.

  Half right Dan.  K&R, page 198, paragraph 3 (sort of):

  "Static and external variables which are not initialized are guaranteed
to start off as 0; automatic and register variables which are not
initialized are guaranteed to start off as garbage."

  Uninitialized data space is cleared (typicaly) by the operating system
for security reasons and to prevent having to have each and every program
do it (not the compiler)...  On the few systems where the OS is known to
not clear the uninitialized data space, then a part of the startup module
in the program is used, but again, it's not "the compiler" that does the
clearing....

>   Anyone programming in C that assumes that malloced memory is zero is
> making a very big mistake.

  Agreed!  Even in the example code shown in K&R, no attempt is made to
clear allocated memory.  (That's what calloc() is for...  :^)

> Dan Wilson

---
John Stanley <dynasoft!john@stag.UUCP>
Software Consultant / Dynasoft Systems