From: Dr Iain Maoileoin <iain@csp-partnership.co.uk>
To: Ken Thompson <kenbob@gmail.com>
Cc: Douglas McIlroy <douglas.mcilroy@dartmouth.edu>,
Alejandro Colomar <alx.manpages@gmail.com>,
TUHS main list <tuhs@tuhs.org>
Subject: [TUHS] Re: origin of null-terminated strings
Date: Fri, 16 Dec 2022 09:13:35 +0000 [thread overview]
Message-ID: <78A69F72-788E-4A31-B750-A39C97F77C75@csp-partnership.co.uk> (raw)
In-Reply-To: <CAMP=X_kUccnyNkSpRxmPY5kY4zWqOGcRXoQkAZE=hNkoiHHO9w@mail.gmail.com>
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ASCIZ
Lost in the mists of time in my mind.
I remember running into a .asciz directive n the 70s “somewhere”.
It was an assembler directive in one of the RT11 systems??? or perhaps the unix bootstrap and/or “.s” files - when I get some time I will go read some old code/manuals.
I
Yes, it put a null byte at the end of a string.
> On 16 Dec 2022, at 03:14, Ken Thompson <kenbob@gmail.com> wrote:
>
> asciz -- this is the first time i heard of it.
> doug -- yes.
>
>
> On Thu, Dec 15, 2022 at 7:04 PM Douglas McIlroy <douglas.mcilroy@dartmouth.edu <mailto:douglas.mcilroy@dartmouth.edu>> wrote:
> I think this cited quote from
> https://www.joelonsoftware.com/2001/12/11/ <https://www.joelonsoftware.com/2001/12/11/> is urban legend.
>
> Why do C strings [have a terminating NUl]? It’s because the PDP-7
> microprocessor, on which UNIX and the C programming language were
> invented, had an ASCIZ string type. ASCIZ meant “ASCII with a Z (zero)
> at the end.”
>
> This assertion seems unlikely since neither C nor the library string
> functions existed on the PDP-7. In fact the "terminating character" of
> a string in the PDP-7 language B was the pair '*e'. A string was a
> sequence of words, packed two characters per word. For odd-length
> strings half of the final one-character word was effectively
> NUL-padded as described below.
>
> One might trace null termination to the original (1965) proposal for
> ASCII, https://dl.acm.org/doi/10.1145/363831.363839 <https://dl.acm.org/doi/10.1145/363831.363839>. There the only
> role specifically suggested for NUL is to "serve to accomplish time
> fill or media fill." With character-addressable hardware (not the
> PDP-7), it is only a small step from using NUL as terminal padding to
> the convention of null termination in all cases.
>
> Ken would probably know for sure whether there's any truth in the
> attribution to ASCIZ.
>
> Doug
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next prev parent reply other threads:[~2022-12-16 9:14 UTC|newest]
Thread overview: 28+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-12-16 3:02 [TUHS] " Douglas McIlroy
2022-12-16 3:14 ` [TUHS] " Ken Thompson
2022-12-16 9:13 ` Dr Iain Maoileoin [this message]
2022-12-16 13:42 ` Dan Halbert
2022-12-16 16:10 ` Dan Cross
2022-12-16 16:22 ` Tom Lyon
2022-12-16 16:29 ` Jon Steinhart
2022-12-16 20:12 ` Dave Horsfall
2022-12-16 21:02 ` Warner Losh
2022-12-16 21:13 ` Clem Cole
2022-12-16 21:49 ` Clem Cole
2022-12-17 0:26 ` Phil Budne
2022-12-16 21:18 ` Luther Johnson
2022-12-16 21:20 ` Dan Halbert
2022-12-16 3:17 ` Steve Nickolas
2022-12-16 17:24 ` John P. Linderman
[not found] ` <6009124d-750d-365e-a424-ec7bb25922b9@gmail.com>
2022-12-16 22:30 ` [TUHS] Terms for string, and similar character constructs (was: origin of null-terminated strings) Alejandro Colomar
2022-12-16 22:51 ` [TUHS] " Dave Horsfall
2022-12-16 22:26 [TUHS] Re: origin of null-terminated strings Douglas McIlroy
2022-12-17 2:03 ` James Frew
2022-12-17 3:42 ` steve jenkin
2022-12-17 17:11 ` Clem Cole
2022-12-17 18:15 ` Tom Lyon
2022-12-17 18:43 ` Clem Cole
2022-12-17 18:46 ` Clem Cole
2022-12-17 19:26 ` Tom Perrine
2022-12-19 4:26 ` Adam Thornton
2022-12-16 23:11 Noel Chiappa
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