linux-kernel - Re: Style Question

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite for Android: free password hash cracker in your pocket

[<prev] [next>] [day] [month] [year] [list]

Message-ID: <2375c9f90703120652w59ca82a5k5e3f4d0ccaee80af@mail.gmail.com>
Date:	Mon, 12 Mar 2007 21:52:02 +0800
From:	"Cong WANG" <xiyou.wangcong@...il.com>
To:	davids@...master.com, linux-kernel@...r.kernel.org,
	"Jan Engelhardt" <jengelh@...ux01.gwdg.de>
Subject: Re: Style Question

2007/3/12, David Schwartz <davids@...master.com>:
>
> > NULL has the same bit pattern as the number zero. (I'm not saying the bit
> > pattern is all zeroes. And I am not even sure if NULL ought to
> > have the same
> > pattern as zero.) So C++ could use (void *)0, if it would let itself :p
>
> They don't have to have the same bit pattern. There's no logical reason a
> NULL pointer couldn't have all bits set and the number zero have all bits
> cleared.
>
> Casts are perrmited to change the bit pattern. For example '(float) 7' can
> result in a different bit pattern than '7' and similarly '(void *) 0' can
> result in a different bit pattern from '0'.
>
> As a trivial example, consider an LP64 system. NULL will have the bit
> pattern of 64 zero bits, while '0' will have the bit pattern of 32 zero
> bits.
>
> DS

I agree. C99 standard just says:

6.3.2.3 Pointers

"3  An integer constant expression with the value 0, or such an
expression cast to type void *, is called a null pointer constant. If
a null pointer constant is converted to a pointer type, the resulting
pointer, called a null pointer, is guaranteed to compare unequal to a
pointer to any object or function."
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/