[TUHS] origin of null-terminated strings

[Dan Halbert]

ASCIZ was an assembler directive used for a number of different DEC 
computers, and also the name for null-terminated strings. I learned it 
for the PDP-10, but I'm sure it existed on other machines. It is in some 
PDP-10 documentation I am looking at right now. Anyone who used DEC and 
did assembly programming would have known about it. Various system calls 
took ASCIZ strings.

On 12/16/22 04:13, Dr Iain Maoileoin wrote:
> 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 at 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 at dartmouth.edu> wrote:
>>
>>     I think this cited quote from
>>     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. 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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