coroutine usage

[Wu zhen hai]

I have the following questions:

1)what is 'coroutine'?
2)'coroutine' purpose?
which advantages can 'coroutine' take?
3)some examples?

[JLBorges]

Boost.Coroutine Introduction explains what coroutines are, why they are useful:
http://www.boost.org/doc/libs/1_63_0/libs/coroutine/doc/html/coroutine/intro.html

A real world example:
https://blogs.msdn.microsoft.com/vcblog/2017/02/02/using-ibuv-with-c-resumable-functions/
Visual Studio 2017 (with a minor keyword change, would also work in VS 2013, and VS 2015)