Re: mysterious destructors
On 2/17/2015 6:22 PM, Stefan Ram wrote:
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.
Nay my friend. You have demonstrated a memory leak.
By assigning another instance to the pointer you lost the first. Raw
pointers do not automatically invoke the destructor when assigned. After
all, you may not want it destroyed, but simply to point to something
else, if you had another way of getting at it, like a second pointer
elsewhere. As is, it is dangling, lost forever.
If you would like to have that behavior, you may want to use a
std::shared_ptr or one of its kin.
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I have chosen to troll filter/ignore all subthreads containing the
words: "Rick C. Hodgins", "Flibble"
So, I won't be able to see or respond to any such messages
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