Each translation unit that includes <iostream> contains a copy of ios_base::Init object:
static ios_base::Init __ioinit;
This object is used to initialize the standard streams (std::cout and its friends). This method is called Schwarz Counter and it ensures that the standard streams are always initialized before their first use (provided iostream header has been included).
That function _GLOBAL__sub_I_main is code the compiler generates for each translation unit that calls the constructors of global objects in that translation unit and also arranges for the corresponding destructor calls to be invoked at exit. This code is invoked by the C++ standard library start-up code before main is called.