Which include file is used during the build process?

Using Arduino Programming Questions
#1

Hello,
I apologize if this is an obvious question or if it has been asked before. I'm new to Arduino IDE. I am confused about the build process, specifically, the include paths. I looked here: http://www.arduino.cc/en/Hacking/BuildProcess but couldn't find the answer to my problem.

I am developing for the esp8266 (refer: esp8266-github). Within "WiFiClient.", the following lines are present:

#include "Client.h"
#include "IPAddress.h"

Since these files don't exist within the "src/" directory there, the pre-processor should look in the other default include paths, correct?

Now the file "IPAddress.h" is present in "Arduino/cores/esp8266/IPAddress.h" as well as "Arduino/hardware/arduino/avr/cores/arduino/IPAddress.h"

So how does it know which one to pick? Which config file, include path or some other setting determines this?

Thank you.

#2

The default paths are searched in the order they are defined. It uses the first one encountered during that search.

#3

Where can I find the default paths?

#4

No idea. It's gotta be in a config file or .ini file or preferences file somewhere underneath where you installed the IDE or out in C:\Users...

If you just want to know which one you are using, simply open one of them up and add a Serial.print in there somewhere where you are sure it will run. Then compile, run, and see if it shows up. If it does, you know that one is being used.

#5