C + + header file has H and no h difference

Can be used directly cout but in iostream, it is defined in the namespace STD, so you must add using namespace std to use cout generally a C + + old with ". h" extension of the library file, For example Iostream.h, in the new standard after the standard library has a non-". h" extension of the corresponding, the difference in addition to many of the latter's improvements, there is one thing is the latter is crammed into the "Std" namespace.

But the string is special.  The problem is that C + + is compatible with the standard library, and C's standard library also happens to have a header file called "String.h", which contains some commonly used C string processing functions, such as the strcmp mentioned by the landlord. This header file has nothing to do with the C + + string class, so it is not an "upgrade version", they are two header files that have no relationship.

C + + header file has H and no h difference