Mega Code Archive
Const auto_ptr
<![CDATA[
/* The following code example is taken from the book
* "The C++ Standard Library - A Tutorial and Reference"
* by Nicolai M. Josuttis, Addison-Wesley, 1999
*
* (C) Copyright Nicolai M. Josuttis 1999.
* Permission to copy, use, modify, sell and distribute this software
* is granted provided this copyright notice appears in all copies.
* This software is provided "as is" without express or implied
* warranty, and with no claim as to its suitability for any purpose.
*/
#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()
{
const auto_ptr<int> p(new int(42));
const auto_ptr<int> q(new int(0));
const auto_ptr<int> r;
cout << "after initialization:" << endl;
cout << " p: " << p << endl;
cout << " q: " << q << endl;
cout << " r: " << r << endl;
*q = *p;
// *r = *p; // ERROR: undefined behavior
*p = -77;
cout << "after assigning values:" << endl;
cout << " p: " << p << endl;
cout << " q: " << q << endl;
cout << " r: " << r << endl;
// q = p; // ERROR at compile time
// r = p; // ERROR at compile time
}
after initialization:
p: 42
q: 0
r: NULL
after assigning values:
p: -77
q: 42
r: NULL
]]>