how to load gamedefault map from VS2015


How can load the default game map with c++ code from Vs2015 ? Based on the converting blueprint project to c++ project, after completion of VS2015 solution file, program can not find the location of game map, which is normally visible and can be set in UE4 editor. Program outputs the /Game/FirstPersonBP/Maps/FirstPersonExampleMap couldn’t be found, how can I eliminate that programatically ?

I also would like to know what is the corresponding source part of loading the maps in UE4 engine, I study the code but that is very tedious task and I’ll appreciate if it can be eased.