Hi all, the question might be not directly related to boost. But i just want to be sure that i am not reventing the wheel. I am searching for a macro that is able to detect that a system is 32bit or 64bit no matter what compiler is used. Is there something similar already implemented in boost? Perhaps some background about this feature. Template specialization for std::size_t is not needed, when the specialization already exists for unsigned int. But on a 64bit system this is not true. So you need explicitly added the specialization whenever a 64bit compiler is used. See the following example. # include <cstddef> template<typename T> struct Null; template<> struct Null<unsigned int> {}; template<> struct Null<std::size_t> {}; // compile only on a 64bit compiler int main() { return 0; }; Thx for any comments, help or suggestions Kim