Re: NUL to terminate strings; was reinventing ASCII?

"James Harris" <james.harris.1@[EMAIL PROTECTED]
> wrote in message
news:44bf8f7a-c1f5-4dbb-a265-0542fdae3bf9@[EMAIL PROTECTED]
> On 10 Mar, 12:13, Ben Bacarisse <ben.use...@[EMAIL PROTECTED]
> wrote:
> > James Harris <james.harri...@[EMAIL PROTECTED]
> writes:
> > > On 8 Mar, 17:22, Ben Bacarisse <ben.use...@[EMAIL PROTECTED]
> wrote:
> > > ...
> > >> So they need a terminating character unless they are defined some
> > >> other way?  Surely the question was why were they not defined in
one
> > >> of these other ways?
> >
> > > Yes, I mean that to allow C strings to be defined as they are by a
> > > single pointer requires there to be a terminating character of some
> > > sort.
> >
> > But this is not true -- at least not literally true.  In BCPL strings
> > were represented by a single pointer, but that pointer was to a
> > length.  I am sure you are not unaware of this kind of representation,
> > I just think you are over-cooking the argument to come up with
> > "requires there to be a terminating character".  I see no such
> > requirement -- it could have been different.
> >
> > I suspect I am reading more into your statement than you intended.
>
> I see your point and appreciate being made to think this through more
> clearly.
> I suppose the bit missing from what I said above is that the
> C concept of a string being an array (of char) allows nowhere for a
> length prefix. If it is an array of char then all elements should be
> of type char.

A string can be an contiguous sequence of char - even with a length
prefix.
Whether it's C compliant is a separate issue.  The header containing the
length just needs to be placed prior to the address representing the start
of the string.

C normally:
----
item[0]  <-- i.e., C's "decayed" pointer points here, start of string data
item[1]
item[2]
item[3]
....
item[length]='\0'  <-- end of string data
....
item[size]  <-- end of allocation for string


In the style of PL/1:
----
length   <-- start of string data, first two items fixed size header
size
item[0]  <-- i.e., C's "decayed" pointer points here
item[1]
item[2]
item[3]
....
item[length-1]  <-- end of string data
item[length]     <-- implicit null character '\0' - not actually set to
null
character
....
item[size]  <-- end of allocation for string


Rod Pemberton