A new bugfix release for kronometer is now available. The release 1.2.2 fixes a small bug that was preventing the compilation with older gcc versions. Since this bug was also well hidden I think that it’s worth a blog post. The bug consisted in two trailing commas forgotten in two enum definitions. Well, actually this is a bug only with certain versions of C and C++ and I didn’t know it. A trailing comma in an enum declaration is a comma after the last enum member:

enum Color {

Let’s see where this code compiles and where it doesn’t (credits to this stackoverflow answer):

  • C89 doesn’t allow the trailing comma
  • C99 does allow it
  • C++98 and C++03 don’t allow it, since their C compatibility is based on C89
  • C++11 does allow it

The default compiler options used by kronometer are: -Wall -Wextra -Werror -ansi -pedantic -std=gnu++0x. Kronometer uses some small features of C++11, like nullptr. That’s why the flag -std=gnu++0x. Here there was the problem: the flag -pedantic triggers a compilation error when it finds the trailing commas. This warning is ignored if C++11 is enabled, but only on recent enough versions of gcc. Since I use gcc 4.8.1 I didn’t find the bug. By removing those commas, now kronometer should be fully compilable also on older compilers.