Using the GNU Compiler Collection (GCC)
5.15 Slightly Looser Rules for Escaped Newlines
Recently, the non-traditional preprocessor has relaxed its treatment of
escaped newlines. Previously, the newline had to immediately follow a
backslash. The current implementation allows whitespace in the form of
spaces, horizontal and vertical tabs, and form feeds between the
backslash and the subsequent newline. The preprocessor issues a
warning, but treats it as a valid escaped newline and combines the two
lines to form a single logical line. This works within comments and
tokens, including multi-line strings, as well as between tokens.
Comments are not treated as whitespace for the purposes of this
relaxation, since they have not yet been replaced with spaces.
