How could I copy the resource of unique_ptr?

[stereoMatching]

std::unique_ptr<int> A(new int(4));
std::unique_ptr<int> B;
B = std::move(A);

I could "move" the resource to B, but how could I copy the resource
to B so B could have a copy of A?

I try it like this

std::unique_ptr<size_t> uPtr_1(new size_t(5) );
std::unique_ptr<size_t> uPtr_2(new size_t(*uPtr_1));

Is this safe?Could you introduce me better methods?
How could I know the type of the unique_ptr?
Thanks a lot

[jsmith]

The second method is as safe as it gets. Line 2 will throw iff the copy constructor of the contained type throws.

template< typename T >
void contained_type( const std::unique_ptr<T>& )
{}

T is the contained type.

OR

std::unique_ptr<T>::element_type is a typedef for T.

[jsmith]

std::unique_ptr<> also has its own move constructor, however both that and your first block above, while equivalent,
are not the same as your second code block. The first block creates only a single int; your second example creates two.

[stereoMatching]

Thanks a lot

I have two more questions
1: is gcc4.5(mingw) realize the move constructor and move assignment of the stl containers already?
I saw the emplace_backmember function when I enable gcc to follow the C++0x
atleast vector and string have the emplace_backmember function

2: looks like gcc4.5(mingw) do not fully implement the unique_ptr yet, because I cannot sort the
elements of the unique_ptr by the std::sort. Is gcc4.6 fix this problem?

[jsmith]

Well, I can't really answer either of your questions because I don't use gcc 4.5 or mingw. However, I can say
that the C++0x standard isn't ratified yet, so any compiler implementation that exists today may change in
the future if more edits are made to the standard before ratification.