What is an undefined reference/unresolved external symbol error and how do I fix it?

Question

What are undefined reference/unresolved external symbol errors? What are common causes and how to fix/prevent them? _{Feel free to edit/add your own.}

Answer 1

It is a linker error. You need to make sure the function you are calling is named correctly.

also you need to make sure you are linking the all object (.o) files and libraries you need.