构造一对unique_ptr <int> 和诠释

Question

I'm trying to create a pair of int and a unique_ptr. How should I use make_pair to create this ?

#include <string>
#include <memory>
#include <algorithm>

int main()
{
    std::unique_ptr<int> p = std::make_unique<int>(0);
    std::pair<int, std::unique_ptr<int>> pr = std::make_pair((int)0, p);
}

I run into the following issue,

Error   C2440   '<function-style-cast>': cannot convert from 'initializer list' to '_Mypair'    templpairuniqueptr  c:\program files (x86)\microsoft visual studio\2017\community\vc\tools\msvc\14.15.26726\include\utility 405 

I could not understand why this happens. I'm on MSVC.

Answer 1

You cannot copy unique pointers. After all, the copy would not be unique. Move instead:

auto pr = std::make_pair(
    0, std::make_unique<int>(0)
);

You can move from lvalues as well, if you need to, by converting the lvalue to an rvalue with std::move :

auto pr = std::make_pair(
    0, std::move(p)
);