Re: [Boost-users] What would happen if boost::shared_ptr is reset to an address in the stack

16 Oct 2007

      on Tue Oct 16 2007, "Peng Yu"  wrote:
...
On 10/16/07, David Abrahams  wrote:
...
on Tue Oct 16 2007, "Peng Yu"  wrote:
...
Hi,
The following program runs well in my system. However, if I change 1
to 0, it will terminate at the line with "delete". Does this mean that
boost::shared_ptr can tell if the pointer is from the stack or the
heap and does different things based on where the pointer is from?
No.  The termination is just an expression of the fact that you invoked
undefined behavior by passing an illegal argument to delete.
...
Thanks,
Peng
#include <iostream>
#include 
int main() {
#if 1//try change this to 0
  int a[100];
  boost::shared_ptr<int> p(a);
  std::cout << std::endl;
#else
  int a[100];
  delete a; // would terminate here
  std::cout << std::endl;
#endif
}
I don't think my question was completely answered. Do you means
reseting shared_ptr with an array from the stack is not defined?
Yes, that's true unless you also supply a custom deleter that has
legal semantics. "delete a" is illegal unless a is dynamically
allocated.

However, it's not what I mean.  I mean that "delete a" is undefined
when a is a stack array.  It's even not legal when it's a heap array
allocated via "a = new int[SIZE]"; for that you'd need "delete[] a"
(which also doesn't work when a is a stack array).

-- 
Dave Abrahams
Boost Consulting
http://www.boost-consulting.com