Q:

How C++ Libraries like POCO can have access to network?

How C++ libraries like POCO can have access to the computer's network and can do networking tasks?
Does POCO use OS's APIs to access network or it use hardware directly to access to network?

A:

On modern operating systems such as Linux/Unix or Windows, applications (and libraries) don't have direct access to hardware. To access network connections, the OS provides APIs like the BSD Sockets API (Linux Manpage) and the Windows adaptation WinSock. Libraries like POCO just provide convenience wrappers around those, possibly adding High-Level protocols like HTTP.

