Avoiding duplicate symbols and retaining code in header files

Question

I have a single global helper function which is used by a bunch of macros in a header file. The intention is to allow the macros to be usable by simply #include

Answer 1

You are only allowed one function definition in your project unless its marked as inline. You may have as many function declarations as you wish (aka function prototypes).

Move your function definition to a .cpp file and just leave the declaration in the header file

void foo(...); // no function body makes this a declaration only

or you could mark it inline:

inline void foo(...) { /* ... */ } 

inline functions should be small and computationally fast as a general rule.