NetNews Offline 2/NetNews Offline Volume 2.iso/news/comp/lang/c++-part2/11052

Text File | 1996-08-05 | 2.6 KB | 97 lines

Newsgroups: comp.lang.c++
Path: news.sprintlink.net!mv!usenet
From: [e-mail] (Michael Furman)
Subject: Re: "Deep" Destructor Query
Message-ID: <[e-mail]>
Mime-Version: 1.0
Content-Type: Text/Plain; charset=US-ASCII
Organization: GSSI
Date: Tue, 12 Mar 1996 14:17:05 GMT
References: <[e-mail]>
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In article <[e-mail]>, [e-mail]
says...
> .... snip
>struct point
>{
>int x, y, z;
>};
>
>Class Shape
>{
>private:
>point *p;  //dynamic array of points
>//...etc
>};
>
>Class Object
>{
>private:
>int numshapes;  //number of data elements
>shape *shapes;  //dynamic array of shapes
>//etc...
>};
>
>Now, this all works quite well, apart from when it comes to destructor
>functions.  For shape I have:
>
>Shape::~Shape()
>{
>if (p)
>        delete [] p;
>}
>
>which works ok.  But when I wrote a destructor for Object, like this:
>
>Object::~Object()
>{
>for (int i = 0; i < numshapes; i++)
>        shapes[i].~shape();  //"Deep" destructor, deletes underlying arrays.
>
>delete [] shapes;  //delete the array of pointers
>}
>
>The program causes a General Protection Fault (guess which OS I'm using and
>win a cookie).  It fails when it tries to delete the array of null pointers
>pointed to by shape.  It works when I leave the "delete [] shapes;" line
out.
>
>Well, I have two questions:
>
>1) If I simply "delete [] shapes" with no loop to delete the arrays
underneath,
>   will the ~shape() destructor be automatically called, thus deleting the
>   shape objects correctly?  I wouldn't think so, but it would be good to be
>   corrected.

Yes (you can check it yourself: just insert "printf(...)" in the destructor,
run program and look at the results).

>
>2) If I delete each shape with a loop (as above), does this mean that shapes
>   pointer points to nothing?  I would have thought that it would point to
>   an array of null pointers.

After you explicitly call destuctor, you have just raw memory - not array
of objects. You can't using "delete" after that (but you can call
"operator delete" to free memory.


>
>Thanks for any comments/opinions/advice.
>
>--
>Peter Hugh Butler

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Michael Furman,                       [phone]
Geophysical Survey Systems, Inc.  fax:[phone]
13 Klein Drive - P.O. Box 97          [e-mail]
North Salem, NH 03073-0097            [e-mail]
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