[TUHS] origins of void*

arnold at skeeve.com arnold at skeeve.com
Mon Nov 6 17:24:38 AEST 2017


Paul Ruizendaal <pnr at planet.nl> wrote:

> >> In the 4BSD era there was caddr_t, which I think was used for pretty
> >> much the same purposes.
> > 
> > Only for kernel code. I am pretty sure caddr_t wasn't used in user-land code.
>
> Ah, thanks for pointing that out, I had not realised that and it helps
> explain some things. But why wasn’t caddr_t used for user-land code:
> usage in the signature of e.g. write() would have made sense, right?

It's clear from K&R 1 that char* served as both pointer to string and
generic pointer to memory.  That's not unreasonable, since, in some sense,
"memory is just bytes".  So user-land code didn't need caddr_t.  I also
suspect that caddr_t came into being with the effort to port Unix off
the PDP-11 and the weight of Unix practice before then had been to make
do with char*.

I think it helps to remember the evolutionary processes that were happening
in the '70s.  High level languages had caught on for application code
(FORTRAN and COBOL in the US, Algol in Europe) but the weight of existing
practice for *systems coding* (operating systems and utilities) had been
to use assembly language.  Multics proved that you could write an OS in
a high level language, but Multics itself (at that time) wasn't a success.

So when C came along in the mid-'70s, strong typing had essentially been
absent from systems programming.  With time and experience, along with
the recognition in the general CS world that strong typing was valuable,
C also started to evolve in that direction.

This is my take on it, anyway. :-)

HTH,

Arnold


More information about the TUHS mailing list