Path: utzoo!attcan!uunet!lll-winken!ames!decwrl!csdpie.dec.com!stacy
From: stacy@csdpie.dec.com
Newsgroups: comp.lang.c++
Subject: Generic vector lib bug fix
Message-ID: <8901121610.AA25201@decwrl.dec.com>
Date: 12 Jan 89 18:40:00 GMT
Organization: Digital Equipment Corporation
Lines: 33

In a recent article, Dominic Samperi writes:
 
> The C++ program below seems to indicate that the generic vector library
> (the one requiring vector.h) contains a bug. I may be using the library
> incorrectly, since it really isn't documented anywhere. The comments
> at the beginning of the program describe the bug, and also point out
> that the bug goes away when a hand-made vector package is used.
 
The problem appears to be in the macro vectorimplement in vector.h(xx).
The operator= member function copies the parameter's elements into
this's elements, but then deletes the array of elements v; although
assignment member functions sometimes legitimately delete such arrays, they
legitimately do this only when they also allocate (and set the
values of) new ones.  Since vector's operator= already requires that 
the parameter vector be of a length equal to this's, no new allocation 
appears necessary, hence no deletion appears necessary.

Commenting out the line (/* delete[i] v; */) in that member function in
that macro (line 55 in my vector.hxx) makes the problem disappear.

BTW, the variable i in that line apparently will have the value -1,
not the original size of the array.

Did I miss the reason why the deletion was there?

Webb Stacy
Softron, Inc.
Waltham, MA

currently at:
stacy%keeper.DEC@decwrl.dec.com
Digital Equipment Corp.
Marlboro, MA