Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Path: utzoo!mnetor!seismo!mimsy!chris From: chris@mimsy.UUCP (Chris Torek) Newsgroups: comp.lang.c Subject: Re: NULL, zero, and readable code Message-ID: <7335@mimsy.UUCP> Date: Mon, 6-Jul-87 04:31:04 EDT Article-I.D.: mimsy.7335 Posted: Mon Jul 6 04:31:04 1987 Date-Received: Tue, 7-Jul-87 00:47:06 EDT References: <8170@brl-adm.ARPA> Organization: U of Maryland, Dept. of Computer Science, Coll. Pk., MD 20742 Lines: 39 In article <8170@brl-adm.ARPA> bdm-thad@Walker-EMH.arpa writes: >I think the problem here is the definition of NULL. NULL is not, repeat, >NOT, equal to zero, at least the base ten zero. If I recall my high >school math, zero is a number, the crossover between positive and nega- >tive. NULL, on the other hand, is the absence of any number. You are mixing definitions wildly. C's NULL is an integer constant zero. A null set is one that contains no elements. The integer or real number zero is the crossover between positive and negative. But C only cares about C's NULL. >ASCII in fact defines them differently: NULL is hex 0 while zero >is hex 30. Now you have brought in another irrelevancy. There are C compilers that do not use ASCII. Besides, code 0/0 in ASCII is NUL, not NULL. >Therefore, stdio.h should define NULL as 0x0, not 0 which would be >0x30. This is all a joke perhaps? C source can be entirely independent of the base character set [*]. Any ASCII-specific code is your own doing. [*Excluding problems with character sets lacking, e.g., left brace or vertical bar. Nonetheless, there are EBCDIC based C compilers out there.] Note that `0x0' is indeed an integer constant zero; it should work as a definition for NULL. But 0 is not equal to 0x30, although '0' may be equal to 0x30 on your machine. >I don't know how most compilers define it. Aztec C, v3.20 for the >IBM, defines it as (void *)0 so I am afraid others may be wrong as well. This has been officially mandated as legal in the proposed standard. I do not like it, but so it goes. -- In-Real-Life: Chris Torek, Univ of MD Comp Sci Dept (+1 301 454 7690) Domain: chris@mimsy.umd.edu Path: seismo!mimsy!chris