Echelon Neuron C - Manual (Page 58)

38 Compiler Directives
...
#else
#ifdef YYY
...
#else
#error “You must define either XXX or YYY”
#endif
#endif
This directive differs from the ANSI C #error directive in that the Neuron C
version requires a quoted string.
#warning “ text ”
This directive allows you to issue a custom warning message. When this
directive is processed, program compilation continues. This directive is
useful for managing conditional compilation, for example:
#ifdef XXX
...
#else
#ifdef YYY
...
#else
#warning “You should define either XXX or YYY”
#endif
#endif