In C, string literals are concatenated automatically. For example,
const char * s1 = "foo" "bar";
const char * s2 = "foobar";
s1
and s2
are the same string.
So, for your problem, the answer (without token pasting) is
#ifdef __TESTING
#define IV_DOMAIN "example.org"
#elif __LIVE_TESTING
#define IV_DOMAIN "test.example.com"
#else
#define IV_DOMAIN "example.com"
#endif
#define IV_SECURE "secure." IV_DOMAIN
#define IV_MOBILE "m." IV_DOMAIN