[TUHS] Re: origin of null-terminated strings

On 16 Dec 2022, at 03:14, Ken Thompson &lt;kenbob(a)gmail.com&gt; wrote: asciz -- this is the first time i heard of it. doug -- yes. On Thu, Dec 15, 2022 at 7:04 PM Douglas McIlroy &lt;douglas.mcilroy(a)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