Pragma

#print a message from the C preprocessor?

Source: https://stackoverflow.com/questions/3826832/is-there-a-portable-way-to-print-a-message-from-the-c-preprocessor

The warning directive is probably the closest you'll get, but it's not entirely platform-independent:

#warning "C Preprocessor got here!"

AFAIK this works on most compilers except MSVC, on which you'll have to use a pragma directive:

#pragma message ( "C Preprocessor got here!" )