Wrong testcase for ##

[keinflue]

The following testcase is not correct:

static void hashhash5()
{
    ASSERT_EQUALS("x1", preprocess("x##__LINE__"));
}

Replacement of macros should happen only after ## has been "evaluated". See §6.10.3.1 and §6.10.3.4 of C11 (n1570), so the corrected test case would be

static void hashhash5()
{
    ASSERT_EQUALS("x__LINE__", preprocess("x##__LINE__"));
}

This also applies if the token(s) next to ## are macro parameters and the corresponding macro argument contains expandable macro names (in contrast to the general behavior of expanding the argument first), meaning that e.g.:

#define X(x) x##__LINE__
#define Y(x) X(x)
X(__LINE__) Y(__LINE__)

should preprocess to __LINE____LINE__ 3__LINE__.

[danmar]

👍