Including an arduino library in Eclipse Neon (undefined reference to)
I don't have eclipse handy right now, so I may not have the menu options verbatim here, but with eclipse there are more steps to including a library than just writing the line in the code.  Go to the project in the project explorer and right click the project name.  Hit import and select the option for importing Arduino libraries into the sketch.  It should bring up a dialog with a list of all the libraries you have installed and you can choose from there.  Then there will be a folder in your project called includes IIRC and it will have a link to the library that you imported.  Now when you compile it will find the library.