How does the custom deleter of std::unique_ptr work?

c++ c++11 unique-ptr delete-operator
Cheers and hth. - Alf picture Cheers and hth. - Alf · Nov 25, 2011 · Viewed 40.6k times · Source

According to N3290, std::unique_ptr accepts a deleter argument in its constructor.

However, I can't get that to work with Visual C++ 10.0 or MinGW g++ 4.4.1 in Windows, nor with g++ 4.6.1 in Ubuntu.

I therefore fear that my understanding of it is incomplete or wrong. I can't see the point of a deleter argument that's apparently ignored, so can anyone provide a working example?

Preferably I'd like to see also how that works for unique_ptr<Base> p = unique_ptr<Derived>( new Derived ).

Possibly with some wording from the standard to back up the example, i.e. that with whatever compiler you're using, it actually does what it's supposed to do?

Answer

Benjamin Lindley picture Benjamin Lindley · Nov 25, 2011

This works for me in MSVC10

int x = 5;
auto del = [](int * p) { std::cout << "Deleting x, value is : " << *p; };
std::unique_ptr<int, decltype(del)> px(&x, del);

And on gcc 4.5, here

I'll skip going to the standard, unless you don't think that example is doing exactly what you'd expect it to do.

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