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From: andrew@teslab.lab.OZ (Andrew Phillips)
Newsgroups: comp.lang.c++
Subject: Order of evaluation bug in Stroustrup?
Message-ID: <1160@teslab.lab.OZ>
Date: 28 Nov 90 06:13:27 GMT
Reply-To: andrew@teslab.lab.oz.au (Andrew Phillips)
Followup-To: comp.lang.c++
Organization: Technology Evaluation Section, L.A.B., Sydney
Lines: 45

In "The C++ Programming Language" by Bjarne Stroustrup, on page 204,
I found the following which I believe to be a bug according to the
rules of C and C++:

  last = last->next = new ...

Since the order of evaluation of subexpressions is undefined it is
unclear whether last in last->next refers to the old value of last or
the newly assigned value of last.  Or am I missing something?


BTW I was surprised to find an even more obvious bug on the next page:

  last = (f==last) ? 0 : f->next;

which should have been:

  if (f == last) last = NULL; else last->next = f->next;

although I believe this was fixed in a later printing.


Also I was surprised to see that what is the first expression in a
for statement in C can be a statement in C++.  Presumably this was
just added for the convenience of being able to declare a variable in
the for loop, so that you can say:

  for (int i = 0; i < max; ++i) ....

But I tried several different kinds of statements in a for loop with
the C++ compiler I use and only some work.  For example this works:

  for ( {int i = 0}  ;  )  ;

but this doesn't:

  for ( for (;;) ;  ;  )  ;


Thanks in advance for any replies to these questions, especially the
first one.

Andrew.
-- 
Andrew Phillips (andrew@teslab.lab.oz.au) Phone +61 (Aust) 2 (Sydney) 289 8712