[Boost-users] [preprocessor] different macro expansion depending on whether its argument is defined or not?

Hi, is it possible to write a preprocessor macro which takes one argument and which expands differently depending on whether the argument is defined or not? Boost solution preferred. Example: #define FOO #undef BAR MY_MACRO(FOO) expands to 1 MY_MACRO(BAR) expands to 0 Kind regards Ingolf