C++11 thread::id special value that represent no thread

Question

This man page states that

Instances of this class may also hold the special distinct value that does not represent any thread.

But I couldn't find nowhere what would be this special value or where it is defined (looked in < thread >). Any ideas?

Answer 1

The default constructor is documented thusly:

Default-constructs a new thread identifier. The identifier does not represent a thread.

So if you want the not-a-thread identifier, just default-construct an id. The default-constructed value can be compared with any thread id to check if the latter is not-a-thread.