Although the library was deprecated for several years, many C++ users still use it in new code instead of using the newer, standard compliant library. What are the differences between the two? First, the .h notation of standard header files was deprecated more than 5 years ago. Using deprecated features in new code is never a good idea. In terms of functionality, contains a set of templatized I/O classes which support both narrow and wide characters. By contrast, classes are confined to char exclusively. Third, the C++ standard specification of iostream’s interface was changed in many subtle aspects. Consequently, the interfaces and implementation of differ from . Finally, components are declared in namespace std whereas components are declared in the global scope.Because of these substantial differences, you cannot mix the two libraries in one program. As a rule, use in new code and stick to in legacy code that is incompatible with the new library.