我读到了如何插入unique_ptr< T>到矢量< unique_ptr< T>>：
Why can I not push_back a unique_ptr into a vector?
但是我如何获得一个元素呢？我做了一个例子：
#include <memory>
#include <vector>
class A {
public:
A(int x,int y){
x_ = x;
y_ = y;
}
private:
int x_;
int y_;
};
int main(){
std::vector<std::unique_ptr<A>> vec_a;
std::unique_ptr<A> tmp_a = std::unique_ptr<A>(new A(13,32));
vec_a.push_back(std::move(tmp_a));
vec_a.push_back(std::unique_ptr<A>(new A(3,2)));
// error
std::unique_ptr<A> a = vec_a.at(0);
}
我收到此错误消息：
main.cc: In function ‘int main()’:
main.cc:24:36: error: use of deleted function
‘std::unique_ptr<_Tp,_Dp>::unique_ptr(const std::unique_ptr<_Tp,_Dp>&)
[with _Tp = A; _Dp = std::default_delete<A>]’
std::unique_ptr<A> a = vec_a.at(0);
^
In file included from /usr/include/c++/4.8/memory:81:0,from main.cc:1:
/usr/include/c++/4.8/bits/unique_ptr.h:273:7: error: declared here
unique_ptr(const unique_ptr&) = delete;
^
我做错了什么？我该怎么办？为什么这不起作用？
