iostream: the ISO C++ input/output library. Also the name of a class within the library, see below.

To write output to and read from standard input in C++ you do:

int age;
string first_name;
cout << "What is your first name and age? ";
cin >> first_name >> age;

cin is an object of class istream, and cout is a member of class ostream.

Similar for files:

int xp;
fstream file("e2.xml");
file << "<xp>" << xp << "</xp>\n";

Simplified family tree of iostream classes:

                                  ios_base                    streambuf
                                      |                           |
                                     ios                          |
                                   /     \                        |
                             istream      ostream        stringbuf, filebuf
                            /       \   /        \
                    ifstream      iostream       ofstream
                           \                    /

*istringstream, ostringstream, stringstream follow the same pattern as ifstream, ofstream, fstream respectively.

ios_base and ios usually are not used by programmers, but are present for base characteristics of the iostream classes. iostream is very easy to extend. An {i,o}stream class takes a streambuf or derived object and buffers output to/from it. It is very easy to write a socketbuf or windowbuf, for example, to input/output to/from a socket or window system.

iostream headers used to be included as #include <iostream.h>, but the current standard uses #include <iostream> - further departing from C. The theory is to lift the concept of include files to a higher level - you are including a library, not a file. However, in practice, this is simply a file called "iostream" rather than "iostream.h". Some compilers (g++) simply wrap a namespace std { #include <iostream.h> }. Others (MSVC) completely rewrote <iostream> to stay current with the moving standard, and leave <iostream.h> as it was (and incompatible with each other).

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