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From: tim@dell.co.uk (Tim Wright)
Newsgroups: comp.unix.sysv386,comp.lang.c
Subject: Re: time(0L) - history of a misconception (was Re: SCO password generator)
Message-ID: <tim.674902529@holly>
Date: 22 May 91 08:55:29 GMT
References: <1991May14.040042.15199@jpradley.jpr.com> <588@sherpa.UUCP> <1141@mwtech.UUCP> <381@tmcsys.UUCP>
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Organization: Dell Computer Corp., Bracknell, UK
Lines: 61

In <381@tmcsys.UUCP> lothar@tmcsys.UUCP (L. Hirschbiegel) writes:

>In article <1141@mwtech.UUCP> martin@mwtech.UUCP (Martin Weitzel) writes:
>>In article <588@sherpa.UUCP> rac@sherpa.UUCP (Roger Cornelius) writes:
>>[...]
>>>	long seed = time(0L);
>>	                 ^^--------- wrong
>>	           time((long *)0);
>>	                ^^^^^^^^^--- right
>>

>You're a cousin of "lint", aren't you :-) ?

>>Note that the argument to the time system call is a `long *', aka
>>pointer to long. 

>Ever tried to RTFM for yourself? 

>	  NAME
>	       time - get time

>	  DESCRIPTION
>	       The time	system call returns the	value of time in seconds
>	       since 00:00:00 Greenwich	Mean Time (GMT), January 1, 1970.

>	       If tloc is non-zero, the	return value is	also stored in the
>                   ^^^^^^^^^^^
>	       location	to which tloc points.

>If you still don't understand: I'll help you! 
>For this little test program:

Yes but it's a pointer i.e. they are talking about a non-zero or non-null
pointer. If the compiler allows prototypes, it can cast a 0 correctly.
Without prototypes it cannot.

>main()
>{
>time(0L);
>time((long *)0);
>}

>the assembler output from my C compiler is:
...
irrelevant :-)

>>Repeat after me: POINTER to long.

>Repeat after me: IT DOESN'T MATTER :-)

*WRONG* *WRONG* *WRONG*. Just because it doesn't happen to matter on
*YOUR* machine with *YOUR* C compiler does not mean it does not matter.
On a non-ansi compliant compiler on a '286 system it is possible to
choose a memory model where sizeof(long) != sizeof(long *).
In this case the code generated will be somewhat different :-)

Tim
-- 
Tim Wright, Dell Computer Corp., Bracknell    |  Domain: tim@dell.co.uk
Berkshire, UK, RG12 1RW. Tel: +44-344-860456  |  Uucp: ...!ukc!delluk!tim
Smoke me a Kipper, I'll be back for breakfast - Red Dwarf