C++ unresolved externals

It means that you have unresolved external symbols.

What are symbols? Symbols can be anything from variables, classes, member functions or functions.

Why they are unresolved? Some part of your code (or libraries that you are using) rely on these symbols and they are not being found because you are not linking the correct library or implementing them.

Yes, it means your program calls functions that are declared but have no body.

Are you expecting these functions to be part of your code, or provided by some library?