Package Name: system.file_control_block
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-- --
-- GNAT RUN-TIME COMPONENTS --
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-- S Y S T E M . F I L E _ C O N T R O L _ B L O C K --
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-- S p e c --
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-- $Revision: 1.7 $ --
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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;
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);
-- 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;
type AFCB_Ptr is access all AFCB'Class;
type AFCB is abstract new Ada.Streams.Root_Stream_Type with record
Stream : Address;
-- 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.
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).
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 : 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 : 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;