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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/
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