https://gcc.gnu.org/bugzilla/show_bug.cgi?id=89410
--- Comment #12 from Jonny Grant <jg at jguk dot org> --- Just to add C spec says UB. http://www.open-std.org/jtc1/sc22/wg14/www/docs/n1256.pdf "The #line preprocessing directive that results after expansion does not match one of the two well-defined forms, or its digit sequence specifies zero or a number greater than 2147483647 (6.10.4)." As I understand it, it is #line <the next line will be numbered> So if it is #line 1, the following line (actual line 2) will be counted as line 1. #line 0, means that the actual 2nd line in a file is treated as 0.
