How to test if preprocessor symbol is #define'd but has no value?

Question

Using C++ preprocessor directives, is it possible to test if a preprocessor symbol has been defined but has no value? Something like that:

#define MYVARIABLE         


        

Answer 1

I want to make sure that the project fails to compile if user forgot to define this string.

While i'd check this in a previous build-step, you can do this at compile-time. Using Boost for brevity:

#define A "a"
#define B
BOOST_STATIC_ASSERT(sizeof(BOOST_STRINGIZE(A)) > 1); // succeeds
BOOST_STATIC_ASSERT(sizeof(BOOST_STRINGIZE(B)) > 1); // fails