I was trying to compile QSctpSocket and QSctpServer out of tree in Windows but the link fails because the QTcpSocketPrivate and other Private parts are not exported.

This is not an issue in Linux or any other OS's. The problem occurs because msvc needs to be told what to export but in gcc and relatives they export everything by default.

To fix, change Q_AUTOTEST_EXPORT to Q_NETWORK_EXPORT in all the exported  _p.h headers, or add it where it's needed like QTcpSocketPrivate and QAbstractSocketPrivate.

The included zip file contains a minimum viable product that will reproduce this issue.