static_assertions.c

// Helper macros to convert a preprocessor token to String 
#define xstr(s) str(s)
#define str(s) #s

// Example of compile time assertions to validate that tha macro argument was not empty
// and avoid building a application that will fail at runtime 
// Clang and gcc are both able to compute this at compile-time, you can use sizeOf() 
// instead of the build-in method here. 
_Static_assert(__builtin_strlen(xstr(OAUTH_CLIENT_ID)) > 0,
"The OAUTH_CLIENT_ID is missing");