Previous preprocessors have allowed extraneous text after a preprocessor directive. For example:
#endif system1
However, the Standard has stated that the only text allowed after a preprocessing directive is a comment. Therefore, the DEC C compiler issues a warning message if this syntax rule is violated.
The numeric value for character constants within #if
and #elif directives matches the value obtained when an
identical character constant occurs in expressions that are not part
of these directives.