What is the <=> (“spaceship”, three-way comparison) operator in C++?

Question

While I was trying to learn about C++ operators, I stumbled upon a strange comparison operator on cppreference.com,^* in a table that looked like

Answer 1

This answer has become irrelevant since the referenced web page has changed

The web page you are referencing was broken. It was being edited a lot that day and different parts was not in sync. The status when I was looking at it was:

At the top of the page it lists the currently existing comparison operators (in C++14). There is no <=>there.

At the bottom of the page, they should have listed the same operators, but they goofed and added this future suggestion.

gcc doesn't know about <=>yet (and with -std=c++14, never will), so it thinks you meant a <= > b. This is explains the error message.

If you try the same thing five years from now you will probably get a better error message, something like <=> not part of C++14.