• Daniel James (19/19) Aug 12 2004 Under certain circumstances macros don't expand correctly.

Daniel James <daniel calamity.org.uk> writes:

Under certain circumstances macros don't expand correctly.

     #define FOO(arg) arg

     #define CALL(x, y) CALL2(x(y))
     #define CALL2(result) result

     CALL(FOO, 1)

This should expand to '1', but it expands to FOO(1).

The same for:

     #define FOO(arg) arg

     #define CALL_ALT(x, y) CALL_ALT_2(x y)
     #define CALL_ALT_2(x) x

     CALL_ALT(FOO, (1))

I've attached some test cases from the wave preprocessor test suite 
which test this kind of thing in more detail. Wave is a highly compliant 
preprocessor implementation which is available from:

The //E lines indicate the expected result of the previous line's macro 
call. Although, I think that very few preprocessors will get 
test13/14/15.cpp right, so they're pretty pathological cases. Maybe only 
wave and gcc's preprocessor will get them right.

Daniel