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From: pal@xanadu.wpd.sgi.com (Anil Pal)
Newsgroups: comp.lang.c++
Subject: Re: new/dispose behavior
Message-ID: <1991Apr30.231252.26736@dragon.wpd.sgi.com>
Date: 30 Apr 91 23:12:52 GMT
References: <1619@msa3b.UUCP>
Sender: news@dragon.wpd.sgi.com (CNews Account)
Reply-To: pal@wpd.sgi.com
Organization: Silicon Graphics, Inc.
Lines: 33

In article <1619@msa3b.UUCP>, kevin@msa3b.UUCP (Kevin P. Kleinfelter) writes:
|> I'm reading along in a book about C++, and I see that one can do:
|> 
|>    char* s = new char [40];
|>    delete s;
|> 
|>    int *p = new int [40];
|>    delete 40 p;
|> 
|> Either I'm confused or the book is!

Actually, both of these examples are incorrect as of the latest draft
of the C++ standard.  The correct way (for both cases) is:

    mumble* x = new mumble[40];
    delete [] x;

Earlier implementations of C++ (for example, those based on cfront 2.0 or
before) required the programmer to explicitly supply the count (40) in the
delete.

What happens if you forget and do a simple delete x; ?  Well, for the
examples quoted (int and char) usually nothing dramatic.  The full
storage will probably be returned to the free pool (in typical
malloc/free based implementations).  If the type mumble is a class with
a destructor, however, forgetting the array form of the delete will
result in a single destructor being called, for the 0-th element in the
array.  Using the array syntax (delete [] x;) will correctly call the
destructor for all elements of the array.

-- 
Anil A. Pal,	Silicon Graphics, Inc.
pal@wpd.sgi.com	(415)-335-7279