The Common File System stream classes consist of three concrete classes that correspond to the three file access modes, and one abstract class.

This file stream class provides input services only and corresponds to the POSIX.1 ORDONLY access mode.

This file stream class provides output services only and corresponds to the POSIX.1 OWRONLY access mode.

This file stream class provides both input and output services, and corresponds to the POSIX.1 ORDWR access mode.

This is an abstract class used to create streams on existing open file descriptors, and to enable you to specify POSIX.1 open modes and flags directly when creating a new file stream. These operations are descripted in detail in Mixing streams and file descriptors.