Question

Why is it wrong to use std::auto_ptr<> with standard containers?

Answer 1

The C++ Standard says that an STL element must be ‘copy-constructible’ and ‘assignable.’ In other words, an element must be able to be assigned or copied and the two elements are logically independent. std::auto_ptr does not fulfill this requirement.

Take for example this code:

class X { };  std::vector<std::auto_ptr<X> > vecX; vecX.push_back(new X);  std::auto_ptr<X> pX = vecX[0];  // vecX[0] is assigned NULL. 

To overcome this limitation, you should use the std::unique_ptr, std::shared_ptr or std::weak_ptr smart pointers or the boost equivalents if you don’t have C++11. Here is the boost library documentation for these smart pointers.