undefined reference when calling inline function

Question

I am getting a really odd error from GCC 4.8.1 with inline functions.

I have two near-identical inline functions defined in header files (debug.h and

Answer 1

According to the manual, passing -std=gnu11 enables C99 instead of GNU inline semantics.

This means inline, static inline and extern inline all behave differently. In particular, inline expects an external definition in a separate translation unit (which you can provide without duplicating the definition - see this answer).