Undefined reference

Most likely culprit is that you've either not defined the function or you included the library with the definition in the wrong order. [source]

In my case it was a bit more insidious - I was the victim of name mangling. Long story short, be extra careful when mixing C and C++. [solution]

The sad thing is I more or less encountered this problem 6 months ago, but I think I have a better understanding of it now.