C++ Primer Plus

Why unique_ptr Is Better than auto_ptr

Consider the following statements:

auto_ptr<string> p1(new string("auto");  //#1auto_ptr<string> p2;                     //#2p2 = p1;                                 //#3

When, in statement #3, p2 takes over ownership of the string object, p1 is stripped of ownership. This, recall, is good because it prevents the destructors for both p1 and p2 from trying to delete the same object. But it also is bad if the program subsequently tries to use p1 because p1 no longer points to valid data.

Now consider the unique_ptr equivalent:

unique_ptr<string> p3(new string("auto");  //#4unique_ptr<string> p4;                     //#5p4 = p3;                                   //#6

In this case, the compiler does not allow ...