[TUHS] Comments on "C"

scj at yaccman.com scj at yaccman.com
Sat Sep 10 03:07:20 AEST 2016


Well, I have a list too -- unfortunately, I had a hand in a couple of
these...

The first is the syntax for casts.  When we were porting Unix from the
PDP-11 to the Interdata (32-bits) we discovered we needed casts badly, but
all of the proposals for syntax sucked.  Since the C grammar was in Yacc
by then, I played around with various ideas, and hit on the "simple"
notion that you just can make a declaration and remove the variable, and
voila, you had something that was unambiguous and, in simple cases, rather
nice -- (int), (int *).  Unfortunately, the sometimes awkward syntax for
declarations got all of its grottiness magnified when condensed into a
cast.  It turned out to be one of those things that was easy to write and
impossible to read.  That said, I'm not a great fan of
static_cast<xxx>(yyy) either...

Another issue is bit fields.  The question is how to lay out the bit
fields in a word -- if you say

union {
    short ss;
    struct {
        int sgn:1;
        int man:15;
    }
};

does sgn refer to the sign bit of ss or the low-order bit?  The answer in
PCC was that it depended on whether the machine was big-endian or
little-endian...    (remember big-endian machines?).

On the one hand, we had little choice, because we wanted int a:8 to act
like char a in a structure.  But the problem was, it made it difficult to
design things, like network protocols, that might communicate between
machines with different byte orders.  Machines like the MIPS, that could
do a sex change with the press of a button, were particularly painful...

With respect to the I/O library, indeed the decision to keep I/O out of
the language was the correct one, especially because I/O in those days
meant tape drives, line printers and punched cards for most machines.  But
the basic library was already there in B, and I believe was lifted, at
least in part, from BCPL.

It tends to be forgotten, but one of the most innovative things in Unix
was the conception of files as arrays of bytes that, because of their
simplicity, could be created almost as afterthoughts.  The mainframes of
the day, and even the time sharing systems built on them, treated file
creation as a big deal.  In the Honeywell time sharing system, you created
files by entering a file-creation subsystem, where you were interactively
asked 10 questions, including the device name, initial size, maximum size,
record size, blocking factor (don't ask!) and who was allowed to write the
file and who was not allowed to read it.  After answering these questions,
the subsystem begged the OS to create a file -- much of the time, it was
allergic to one of the answers, and required you to go through all the
questions again.  If you got through the process unscathed, the system
printed out "Successful!"
(yes, the exclamation point was there).

I remember in early days showing someone Unix and typing
    echo hello >foo
and showing them that foo was now a file.  The usual response was a gasp
and a dropped jaw, followed by confusion...

Steve












>> After about 30 years of C, there are only three things I would
> have liked to see:
>




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