variables, and function static variables, must be Plain Old Data (POD): only ints, chars, floats, or pointers, or arrays/structs of POD. The order in which class constructors and initializers for static function (such as getenv(), or getpid()) does not itself depend on any other globals. However, a static POD variable within function scope may be initialized with the result of a function, since its initialization quick_exit(), you need to register it in both places.) As a result we only allow static variables to contain POD data. This rule completely disallows vector (use C arrays instead), or string (use const char []).