Re: ANSI C and POSIX (was Re: C/C++ knocks the crap out of Ada)

[dewar@cs.nyu.edu (Robert Dewar)]

John suggested

"    /* Try to protect the user a little bit from left over garbage: */
    memset(&buf[avail], nbytes-avail, 0);  /* zero out buf[avail..nbytes-1] */
    return avail;"

Interesting, the spec is really not clear on whether this is a valid
implementation. I can easily imagine a programmer whose unwritten
rules would rule out this interpretation and who might assume that
code which

  (a) preinitialized the buffer to blanks
  (b) used read to read into part of this buffer

should be able to expect trailing spaces and not zeroes,

but here again, the spec is insufficiently clear I would say, so this is
another nice example of possible portability problems that come from
a vague spec.

That trailing spaces code will probably work in most (all) implementations
of read, and I can imagine some (injudicious? or perhaps informed by
a different set of "unwritten rules") programmer assuming it would work.
Then an implementatoin would do as John suggested, which certainly is
not unreasonable, and lo and behold, another portability problem that
could have been prevented by a precise spec.