initialize a static const value outside of Constructor only for integral types

class A{private: static const int a = 4; // valid static const std::string t ; // can't be initialized here ... ...};// in a cpp file where the static variable will exist const std::string A::t = "this way it works";

Also, note that this rule have been removed in C++11, now (with a compiler providing the feature) you can initialize what you want directly in the class member declaration.