C 11 unique_ptr和shared_ptr是否能够转换为彼此的类型？

C 11标准库是否提供了从std :: shared_ptr转换为std :: unique_ptr的任何实用程序,反之亦然？这是安全的操作吗？

解决方法:

std::unique_ptr is the C++11 way to express exclusive ownership, but one of its
most attractive features is that it easily and efficiently converts to a std::shared_ptr.

This is a key part of why std::unique_ptr is so well suited as a factory function return type. Factory functions can’t know whether callers will want to use exclusive ownership semantics for the object they return or whether shared ownership (i.e., std::shared_ptr) would be more appropriate. By returning a std::unique_ptr, factories provide callers with the most efficient smart pointer, but they don’t hinder callers from replacing it with its more flexible sibling.

std::shared_ptr to std::unique_ptr is not allowed. Once you’ve turned lifetime management of a resource over to a std::shared_ptr, there’s no changing your mind. Even if the reference count is one, you can’t reclaim ownership of the resource in order to, say, have a std::unique_ptr manage it.

Reference: Effective Modern C++. 42 SPECIFIC WAYS TO IMPROVE YOUR USE OF C++11 AND C++14. Scott Meyers.

简而言之,您可以轻松有效地将std :: unique_ptr转换为std :: shared_ptr,但不能将std :: shared_ptr转换为std :: unique_ptr.

例如：

std::unique_ptr<std::string> unique = std::make_unique<std::string>("test");
std::shared_ptr<std::string> shared = std::move(unique);

要么：

std::shared_ptr<std::string> shared = std::make_unique<std::string>("test");

标签：c,c11,shared-ptr,unique-ptr
来源： https://codeday.me/bug/20190930/1834708.html