Including header files does not find the functions included in them

Question

I am currently writing code to read the battery voltage using the C language. I would like to include the header file "es_battery_voltage.h" and use the two functions "es_battery_voltage_get()" and "es_battery_voltage_init()". However, even though I have included the above header files, I get an error that the functions cannot be found. The actual error message is attached below. Thank you very much for your help. 
 
 undefined reference to `es_battery_voltage_init' 
 undefined reference to `es_battery_voltage_get' 
 
 LemonCake

Jared · Answer

Hi, 
 You also need to add the path and source file to the project. See this if you're using SES. 
 regards Jared