mark s. ogilvie

I'm just starting with "The C++ standard Library, a tutorial and reference
by Nicolai Josuttis(10th printing) and that auto_ptr example is not working
properly. When I run this:

#include <iostream>
#include <memory>
using namespace std;

/* define output operator for auto_ptr
* - print object value or NULL
*/
template <class T>
ostream& operator<< (ostream& strm, const auto_ptr<T>& p)
{
// does p own an object ?
if (p.get() == NULL) {
strm << "NULL"; // NO: print NULL
}
else {
strm << *p; // YES: print the object
}
return strm;
}

int main()
{
auto_ptr<int> p(new int(42));
auto_ptr<int> q;

cout << "after initialization:" << endl;
cout << " p: " << p << endl;
cout << " q: " << q << endl;

q = p;
cout << "after assigning auto pointers:" << endl;
cout << " p: " << p << endl;
cout << " q: " << q << endl;

*q += 13; // change value of the object q owns
p = q;
cout << "after change and reassignment:" << endl;
cout << " p: " << p << endl;
cout << " q: " << q << endl;
}

Which is the example in the book, I get

after initialization:
p: 42
q: NULL
after assigning auto pointers:
p: 42
q: 42
after change and reassignment:
p: 55
q: 55
Press any key to continue

Not what I should get according to both the book and my understanding of
auto-pointers. I've check the Josuttis home page and it is not listed under
erata or compilier quirks. I am using Microsoft visual c++ version 6.0.
Could the problem be somewhere in the build settings? Or does visuall c+
simply handle auto_ptr like this?

Mark

andré_pönitz

The result should be

after initialization:
p: 42
q: NULL
after assigning auto pointers:
p: NULL
q: 42
after change and reassignment:
p: 55
q: NULL


That might be the problem.

MSVC++ 6.0 hardly qualifies as C++ compiler when it comes to Standard
C++.

g++ gets it right btw.

Andre'

guy harrison

^^^
Bad. It should have handed over ownership here.

It may be but you'd be best off checking on a VC group. This can't have gone unoticed.


If it does, then its auto_ptr may as well not exist. Take a look in the FAQ.
It never hurts to have more than one compiler.


--
Guy Harrison

mark s. ogilvie

I've been thinking about getting another compiler for non windows
programing. This is a good reason.

Thanks

Mark