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--                                                                          --

--                         GNAT RUN-TIME COMPONENTS                         --

--                                                                          --

--              S Y S T E M . F I L E _ C O N T R O L _ B L O C K           --

--                                                                          --

--                                 S p e c                                  --

--                                                                          --

--            Copyright (C) 1992-2011, Free Software Foundation, Inc.       --

--                                                                          --

-- GNAT is free software;  you can  redistribute it  and/or modify it under --

-- terms of the  GNU General Public License as published  by the Free Soft- --

-- ware  Foundation;  either version 3,  or (at your option) any later ver- --

-- sion.  GNAT is distributed in the hope that it will be useful, but WITH- --

-- OUT ANY WARRANTY;  without even the  implied warranty of MERCHANTABILITY --

-- or FITNESS FOR A PARTICULAR PURPOSE.                                     --

--                                                                          --

-- As a special exception under Section 7 of GPL version 3, you are granted --

-- additional permissions described in the GCC Runtime Library Exception,   --

-- version 3.1, as published by the Free Software Foundation.               --

--                                                                          --

-- You should have received a copy of the GNU General Public License and    --

-- a copy of the GCC Runtime Library Exception along with this program;     --

-- see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see    --

-- <http://www.gnu.org/licenses/>.                                          --

--                                                                          --

-- GNAT was originally developed  by the GNAT team at  New York University. --

-- Extensive contributions were provided by Ada Core Technologies Inc.      --

--                                                                          --

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--  This package contains the declaration of the basic file control block

--  shared between Text_IO, Sequential_IO, Direct_IO and Streams.Stream_IO.

--  The actual control blocks are derived from this block by extension. The

--  control block is itself derived from Ada.Streams.Root_Stream_Type which

--  facilitates implementation of Stream_IO.Stream and Text_Streams.Stream.

with Ada.Streams;

with Interfaces.C_Streams;

with System.CRTL;

package System.File_Control_Block is

   ----------------------------

   -- Ada File Control Block --

   ----------------------------

   --  The Ada file control block is an abstract extension of the root

   --  stream type. This allows a file to be treated directly as a stream

   --  for the purposes of Stream_IO, or stream operations on a text file.

   --  The individual I/O packages extend this type with package specific

   --  fields to create the concrete types to which the routines in this

   --  package can be applied.

   --  The type File_Type in the individual packages is an access to the

   --  extended file control block. The value is null if the file is not

   --  open, and a pointer to the control block if the file is open.

   type Pstring is access all String;

   --  Used to hold name and form strings

   type File_Mode is (In_File, Inout_File, Out_File, Append_File);

   subtype Read_File_Mode is File_Mode range In_File .. Inout_File;

   --  File mode (union of file modes permitted by individual packages,

   --  the types File_Mode in the individual packages are declared to

   --  allow easy conversion to and from this general type.

   type Shared_Status_Type is (Yes, No, None);

   --  This type is used to define the sharing status of a file. The default

   --  setting of None is used if no "shared=xxx" appears in the form string

   --  when a file is created or opened. For a file with Shared_Status set to

   --  None, Use_Error will be raised if any other file is opened or created

   --  with the same full name. Yes/No are set in response to the presence

   --  of "shared=yes" or "shared=no" in the form string. In either case it

   --  is permissible to have multiple files opened with the same full name.

   --  All files opened simultaneously with "shared=yes" will share the same

   --  stream with the semantics specified in the RM for file sharing. All

   --  files opened with "shared=no" will have their own stream.

   type AFCB is tagged;

   type AFCB_Ptr is access all AFCB'Class;

   type AFCB is abstract new Ada.Streams.Root_Stream_Type with record

      Stream : Interfaces.C_Streams.FILEs;

      --  The file descriptor

      Name : Pstring;

      --  A pointer to the file name. The file name is null for temporary

      --  files, and also for standard files (stdin, stdout, stderr). The

      --  name is always null-terminated if it is non-null.

      Encoding : System.CRTL.Filename_Encoding;

      --  Encoding used to specified the filename

      Form : Pstring;

      --  A pointer to the form string. This is the string used in the

      --  fopen call, and must be supplied by the caller (there are no

      --  defaults at this level). The string is always null-terminated.

      Mode : File_Mode;

      --  The file mode. No checks are made that the mode is consistent

      --  with the form used to fopen the file.

      Is_Regular_File : Boolean;

      --  A flag indicating if the file is a regular file

      Is_Temporary_File : Boolean;

      --  A flag set only for temporary files (i.e. files created using the

      --  Create function with a null name parameter, using tmpfile). This

      --  is currently not used since temporary files are deleted by the

      --  operating system, but it is set properly in case some systems

      --  need this information in the future.

      Is_System_File : Boolean;

      --  A flag set only for system files (stdin, stdout, stderr)

      Is_Text_File : Boolean;

      --  A flag set if the file was opened in text mode

      Shared_Status : Shared_Status_Type;

      --  Indicates sharing status of file, see description of type above

      Access_Method : Character;

      --  Set to 'Q', 'S', 'T', 'D' for Sequential_IO, Stream_IO, Text_IO,

      --  Direct_IO file (used to validate file sharing request).

      Next : AFCB_Ptr;

      Prev : AFCB_Ptr;

      --  All open files are kept on a doubly linked chain, with these

      --  pointers used to maintain the next and previous pointers.

   end record;

   ----------------------------------

   -- Primitive Operations of AFCB --

   ----------------------------------

   --  Note that we inherit the abstract operations Read and Write from

   --  the base type. These must be overridden by the individual file

   --  access methods to provide Stream Read/Write access.

   function AFCB_Allocate (Control_Block : AFCB) return AFCB_Ptr is abstract;

   --  Given a control block, allocate space for a control block of the same

   --  type on the heap, and return the pointer to this allocated block. Note

   --  that the argument Control_Block is not used other than as the argument

   --  that controls which version of AFCB_Allocate is called.

   procedure AFCB_Close (File : not null access AFCB) is abstract;

   --  Performs any specialized close actions on a file before the file is

   --  actually closed at the system level. This is called by Close, and

   --  the reason we need the primitive operation is for the automatic

   --  close operations done as part of finalization.

   procedure AFCB_Free (File : not null access AFCB) is abstract;

   --  Frees the AFCB referenced by the given parameter. It is not necessary

   --  to free the strings referenced by the Form and Name fields, but if the

   --  extension has any other heap objects, they must be freed as well. This

   --  procedure must be overridden by each individual file package.

end System.File_Control_Block;