c++
Possible Duplicate:
std::auto_ptr to std::unique_ptr
What C++ Smart Pointer Implementations are available?
Lets say I have this struct :
struct bar
{
};
When I use auto_ptr like this:
void foo()
{
auto_ptr<bar> myFirstBar = new bar;
if( )
{
auto_ptr<bar> mySecondBar = myFirstBar;
}
}
then at auto_ptr<bar> mySecondBar = myFirstBar; C++ transfers the ownership from myFirstBar to mySecondBar and there is no compilation error.
But when I use unique_ptr instead of auto_ptr I get a compiler error. Why C++ doesn't allow this? And what is the main differences between these two smart pointers? When I need to use what?
std::auto_ptr<T> may silently steal the resource. This can be confusing and it was tried to defined std::auto_ptr<T> to not let you do this. With std::unique_ptr<T> ownership won't be silently transferred from anything you still hold. It transfers ownership only from objects you don't have a handle to (temporaries) or which are about to go away (object about to go out of scope in a function). If you really want to transfer ownership, you'd use std::move() :
std::unique_ptr<bar> b0(new bar());
std::unique_ptr<bar> b1(std::move(b0));
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