NetNews Usenet Archive 1992 #19/NN_1992_19.iso/spool/comp/lang/cplus/12886

Internet Message Format | 1992-08-25 | 2.9 KB

Path: sparky!uunet!cs.utexas.edu!sun-barr!ames!agate!agate!matt
From: [e-mail] (Matt Austern)
Newsgroups: comp.lang.c++
Subject: Re: Novice Questions
Date: 25 Aug 92 19:30:32
Organization: Lawrence Berkeley Laboratory (Theoretical Physics Group)
Lines: 45
Distribution: usa
Message-ID: <[e-mail]>
References: <[e-mail]>
    <[e-mail]>
Reply-To: [e-mail]
NNTP-Posting-Host: physics16.berkeley.edu
In-reply-to: [e-mail]'s message of Wed, 26 Aug 1992 00:11:50 GMT

In article <[e-mail]> [e-mail] (Paul Lucas) writes:

> >syntax?  I'm writing a simple program that does different types of string
> >reversing and thought that I should call a function with a string, and then
> >return that string reversed in different ways.
>
> *****>    Array names (almost) always decay into a pointer to the first
>     element, so _that's_ what you return--a pointer.

Yes and no.  This answer is correct, but, depending on what the
original user wanted, not necessarily useful.  My impression was that
he wanted to treat arrays (including strings, which, in C, are just
arrays of characters) as first-class objects.  Pointer manipulation is
useful, but it isn't the same thing at all.

(And one problem with returning a pointer to an array instead of
returning an array is just that a pointer has to point to something!
As people have already observed in the thread on garbage collection,
this means that when a function returns a pointer, part of the
interface of that function must be an explicit protocol on who
allocates and deallocates that storage.)

For example: if arrays were first-class objects, then, if A is an
array, and foo() was a function which returns an array, you could
write
        A = foo().
Of course, this isn't possible with the built-in C types; that is, if
A is declared as "double A[NUM_ELTS]", and foo is declared as "double
*foo()", then this code is illegal.

Fortunately, this is only half of the story.  I have carefully written
"C" up until now instead of "C++", because there is a better way in
C++: you can declare your own types, e.g., Array, or String, and you
can treat these types as first-class data types---you can use the
assignment operator for objects of type Array or String, and you can
return them from functions.

The only down side of this is that you have to define Array and String
yourself, or pick them up from some class library; there isn't yet a
Standard Class Library that is defined along with the C++ language.
--
Matthew Austern                   Just keep yelling until you attract a
[phone]                    crowd, then a constituency, a movement, a
[e-mail]                faction, an army!  If you don't have any
[e-mail]         solutions, become a part of the problem!