mysterious destructors

From:
ram@zedat.fu-berlin.de (Stefan Ram)
Newsgroups:
comp.lang.c++
Date:
18 Feb 2015 00:22:23 GMT
Message-ID:
<destructors-20150218010557@ram.dialup.fu-berlin.de>
  I have written the following program:

#include <iostream>
#include <ostream>

struct c
{ int v;

  c( int const x ): v( x )
  { ::std::cout << "constructor of instance #" << v << ".\n"; }

  ~c(){ ::std::cout << "destructor of instance #" << v << ".\n"; }

  void print(){ ::std::cout << "I am instance #" << v << ".\n"; }};

int main()
{ c o = * new c( 1 );
    o.print();
    o = * new c( 2 ); /* overwrite */
    o.print(); }

  The program prints:

constructor of instance #1.
I am instance #1.
constructor of instance #2.
I am instance #2.
destructor of instance #2.

  In the line marked with ?/* overwrite */?, instance #1 in the
  variable ?o? is overwritten with another instance of the same
  class c if I understand it correctly.

  I thought that this overwriting kind-of ?destroys? the instance #1
  and that this might invoke the destructor of instance #1. But no,
  it does never print ?destructor of instance #1.?.

  I am still a beginner with respect to some parts of C++, so
  I have to ask here why my expectations are wrong.

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