Alex Fenton wrote:
> In C extension code, what's the canonical way to test whether the ruby  
> being compiled against is 1.8 or 1.9?
> [...]
> But this seems accidental. However I didn't find a RUBY_VERSION constant  
> in the headers anywhere.
> [...]

Have you looked at version.h?

# head -n12 ruby-1.9-svn/version.h
#define RUBY_VERSION "1.9.0"
#define RUBY_RELEASE_DATE "2008-11-10"
#define RUBY_VERSION_CODE 190
#define RUBY_RELEASE_CODE 20081110
#define RUBY_PATCHLEVEL 0

#define RUBY_VERSION_MAJOR 1
#define RUBY_VERSION_MINOR 9
#define RUBY_VERSION_TEENY 0
#define RUBY_RELEASE_YEAR 2008
#define RUBY_RELEASE_MONTH 11
#define RUBY_RELEASE_DAY 10

Regards,
Daniel