在 c++ 中调用构造函数的正确方法是什么？

Question

    Communicator communicator = Communicator();

    Communicator communicator;

What is the difference between these 2 calls?

Answer 1

The difference is in copy elision. Before C++17, in the line

Communicator communicator = Communicator();

a temporary Communicator object was created and then used to copy-construct communicator . A compiler could optimize this out but it had to check that that copy or move constructor can be invoked (public, not deleted, not explicit ).

Since C++17, copy elision rules have changes: "unmaterialized value passing" was introduced. Now in that line no temporary object is created and no copy/move constructor is needed.

The following simple code will compile in C++17, but will fail to compile in C++11/14:

class Communicator {
public:
    Communicator() = default;
    Communicator(const Communicator&) = delete;
};

Communicator c = Communicator();