I have a C++ library originally developed in VS2015 which uses SOCKET from Winsock2 inside Windows SDK 8.1. The solution file is generated from a cmake file, and it builds perfectly fine. I use the same cmake file to create the solution again in VS2017. However, I can not compile it unless I add #include <WinSock2.h> at the file where SOCKET is being used. It looks like it's not picking up the definition of SOCKET unless I explicitly include the WinSock2.h file. And I don't need to do that in VS2015.

I checked the project properties and they look the same and are both using Windows SDK 8.1. So what is the difference here with VS2015 and VS2017? Does VS2015 automatically include windows SDK header files but not in VS2017?