Boost has preprocessor macro named BOOST_PP_ASSERT_MSG:

But this only works for string constants. What if You need to debug Your C++ compile-time metaprogram and want to output some numbers unknown at the time of writing the code?

 

 

#include <boost/preprocessor/stringize.hpp> #include <boost/preprocessor/arithmetic/dec.hpp> #include <boost/preprocessor/cat.hpp> #include <boost/preprocessor/repetition/repeat.hpp> #include <boost/preprocessor/arithmetic/add.hpp>   #define FILE_AND_LINE_MESSAGE     MESSAGE(__FILE__ " : " BOOST_PP_STRINGIZE(__LINE__) " :")   #define PP_DEC0(v)      BOOST_PP_IF(v, BOOST_PP_DEC(v), -1)   //allows decrementing from the value 0 too   #if defined(_MSC_VER) && (_MSC_VER >= 1400)     #define MESSAGE2(x) __pragma (message(BOOST_PP_STRINGIZE(x)))     #define MESSAGE(x)  __pragma (message(x))  #else       #include <boost/preprocessor/debug/assert.hpp>       #define MESSAGE2(x) BOOST_PP_ASSERT_MSG(1, BOOST_PP_STRINGIZE(x))     #define MESSAGE(x)  BOOST_PP_ASSERT_MSG(1, x)         #endif   #ifdef __cplusplus       template <int val, int dummyI>     struct numeric_message;         #define DEFINE_NUMERIC_MESSAGE_T(z, n, data)   template <int dummyI> struct numeric_message<n - 1, dummyI> { numeric_message() { MESSAGE(BOOST_PP_STRINGIZE(BOOST_PP_CAT(val :, PP_DEC0(n)))) }; };         #ifndef MAX_NUMERIC_MESSAGE         #define MAX_NUMERIC_MESSAGE  128     #endif         #if defined(BOOST_PP_REPEAT) && defined(BOOST_PP_ADD)         BOOST_PP_REPEAT(BOOST_PP_ADD(MAX_NUMERIC_MESSAGE, 2), DEFINE_NUMERIC_MESSAGE_T,)        #endif     #define NUMERIC_MESSAGE(val)   numeric_message<val, __COUNTER__> BOOST_PP_CAT(__numeric_message__, __COUNTER__);   //counter is evaluated during compile time, not preprocessing time, so it is ok to use it here     #define NUMERIC_MESSAGE2(val)  FILE_AND_LINE_MESSAGE NUMERIC_MESSAGE(val)   // TODO: currently the line numbers are printed before other stuff   #endif  //#ifdef __cplusplus