How do you anchor galvanized fence post to concrete to erect a fence on a slab

So you are talking about a galvanized pipe and not a wooden fence, right? The best way is to drill a 3" hole through the concrete with a rotary hammer. Go into the soil as deep as your hammer will reach and drive the pipe in about 2', fill the remainder of the hole with patching cement or vinyl concrete.

You could use a base flange that would lag into the slab as well. Check out Hollaender Speed-Rail system.