This chapter describes the most common NSPR types, enumerations, and
structures used with the functions described in `I/O
Functions <I%2f%2fO_Functions>`__ and `Network
Addresses <Network_Addresses>`__. These include the types used for
system access, normal file I/O, and socket (network) I/O.

Types unique to a particular function are described with the function
itself.

For sample code that illustrates basic I/O operations, see `Introduction
to NSPR <Introduction_to_NSPR>`__.

-  `Directory Type <#Directory_Type>`__
-  `File Descriptor Types <#File_Descriptor_Types>`__
-  `File Info Types <#File_Info_Types>`__
-  `Network Address Types <#Network_Address_Types>`__
-  `Types Used with Socket Options
   Functions <#Types_Used_with_Socket_Options_Functions>`__
-  `Type Used with Memory-Mapped
   I/O <#Type_Used_with_Memory-Mapped_I/O>`__
-  `Offset Interpretation for Seek
   Functions <#Offset_Interpretation_for_Seek_Functions>`__

.. _Directory_Type:

Directory Type
--------------

 - :ref:`PRDir`

.. _File_Descriptor_Types:

File Descriptor Types
---------------------

NSPR represents I/O objects, such as open files and sockets, by file
descriptors of type :ref:`PRFileDesc`. This section introduces
:ref:`PRFileDesc` and related types.

 - :ref:`PRFileDesc`
 - :ref:`PRIOMethods`
 - :ref:`PRFilePrivate`
 - :ref:`PRDescIdentity`

Note that the NSPR documentation follows the Unix convention of using
the term\ *files* to refer to many kinds of I/O objects. To refer
specifically to the files in a file system (that is, disk files), this
documentation uses the term\ *normal files*.

:ref:`PRFileDesc` has an object-oriented flavor. An I/O function on a
:ref:`PRFileDesc` structure is carried out by invoking the corresponding
"method" in the I/O methods table (a structure of type :ref:`PRIOMethods`)
of the :ref:`PRFileDesc` structure (the "object"). Different kinds of I/O
objects (such as files and sockets) have different I/O methods tables,
thus implementing different behavior in response to the same I/O
function call.

NSPR supports the implementation of layered I/O. Each layer is
represented by a :ref:`PRFileDesc` structure, and the :ref:`PRFileDesc`
structures for the layers are chained together. Each :ref:`PRFileDesc`
structure has a field (of type :ref:`PRDescIdentity`) to identify itself in
the layers. For example, the Netscape implementation of the Secure
Sockets Layer (SSL) protocol is implemented as an I/O layer on top of
NSPR's socket layer.

.. _File_Info_Types:

File Info Types
---------------

 - :ref:`PRFileInfo`
 - :ref:`PRFileInfo64`
 - :ref:`PRFileType`

.. _Network_Address_Types:

Network Address Types
---------------------

 - :ref:`PRNetAddr`
 - :ref:`PRIPv6Addr`

.. _Types_Used_with_Socket_Options_Functions:

Types Used with Socket Options Functions
----------------------------------------

 - :ref:`PRSocketOptionData`
 - :ref:`PRSockOption`
 - :ref:`PRLinger`
 - :ref:`PRMcastRequest`

.. _Type_Used_with_Memory-Mapped_I.2FO:

Type Used with Memory-Mapped I/O
--------------------------------

 - :ref:`PRFileMap`

.. _Offset_Interpretation_for_Seek_Functions:

Offset Interpretation for Seek Functions
----------------------------------------

 - :ref:`PRSeekWhence`