Ada Programming/Libraries/Ada.Sequential_IO

This language feature is available from Ada 95 on.

Ada. Time-tested, safe and secure.
Ada. Time-tested, safe and secure.

Ada.Sequential_IO is a unit of the Predefined Language Environment since Ada 95.

Background edit

Not all data read or written is in text format. For storage or inter-process communication, it is more space- and processing time-efficient to store data in binary format.

Binary input and output for sequential data (that is, read/written one after another) is managed by the generic Ada package Ada.Sequential_IO.

The generic package must be instantiated with some Element_Type, and provides a limited private File_Type.

The file mode, In_File or Out_File, is established on open or create.

The package provides the basic input/output (I/O) operations:

  • Open, Create
  • Close, Delete, and Reset
  • Read, Write

In addition, the package provides status and information functions:

  • Is_Open
  • End_Of_File
  • Name, Mode, and Form

One important restriction is that every element of a file must be the same element type.

Ada Code Example edit

For example, suppose that a student has collected information on trees in a 10 meter by 10 meter plot, and wishes a report generated from the data.
The following is a simple program to read the sequential data, previously recorded:

  with Ada.Text_IO; --  Text I/O library
  with Ada.Float_Text_IO; --  Float I/O library
  with Ada.Sequential_IO; --  Sequential I/O library

  procedure Tree_Report is
  --  First, define the contents of the data record

     type Tree_Record is 
           Common_Name     : String(1..20) := (others => ' ');
           Scientific_Name : String(1..20) := (others => ' ');
           Diameter        : Float         := 0.0; --  at breast height (DBH)
        end record; --  Tree_Record
--  Now, instantiate the I/O package for the data record

     package Tree_IO is new Ada.Sequential_IO(Tree_Record);
     Tree_File : Tree_IO.File_Type; --  Input data file
     Tree_Data : Tree_Record; --  Individual data record
  begin --  Tree_Report
--  Open the input data file.

     Tree_IO.Open(File => Tree_File,
                  Mode => Tree_IO.In_File,
                  Name => "tree.dat");
  --  Write report heading
     Ada.Text_IO.Set_Col(To =>  1); Ada.Text_IO.Put("COMMON NAME");
     Ada.Text_IO.Set_Col(To => 21); Ada.Text_IO.Put("SCIENTIFIC NAME");
     Ada.Text_IO.Set_Col(To => 41); Ada.Text_IO.Put("DBH");
     while not Tree_IO.End_Of_File(Tree_File) loop
        Tree_IO.Read(Tree_File, Tree_Data); --  Read tree data
     --  Write tree inventory
     end loop Process_Tree_Data;
--  All data records have been read, and end_of_file detected.

     Tree_IO.Close(Tree_File); --  Done, close file
  end Tree_Report;

Specification edit

--                     Standard Ada library specification
--   Copyright (c) 2003-2018 Maxim Reznik <>
--   Copyright (c) 2004-2016 AXE Consultants
--   Copyright (c) 2004, 2005, 2006 Ada-Europe
--   Copyright (c) 2000 The MITRE Corporation, Inc.
--   Copyright (c) 1992, 1993, 1994, 1995 Intermetrics, Inc.
--   SPDX-License-Identifier: BSD-3-Clause and LicenseRef-AdaReferenceManual
-- -------------------------------------------------------------------------

with Ada.IO_Exceptions;
   type Element_Type (<>) is private;
package Ada.Sequential_IO is

   type File_Type is limited private;

   type File_Mode is (In_File, Out_File, Append_File);

   --  File management

   procedure Create (File : in out File_Type;
                     Mode : in File_Mode := Out_File;
                     Name : in String := "";
                     Form : in String := "");

   procedure Open  (File : in out File_Type;
                    Mode : in File_Mode;
                    Name : in String;
                    Form : in String := "");

   procedure Close (File : in out File_Type);
   procedure Delete (File : in out File_Type);
   procedure Reset (File : in out File_Type; Mode : in File_Mode);
   procedure Reset (File : in out File_Type);

   function Mode   (File : in File_Type) return File_Mode;
   function Name   (File : in File_Type) return String;
   function Form   (File : in File_Type) return String;

   function Is_Open (File : in File_Type) return Boolean;

   --  Input and output operations

   procedure Read  (File : in File_Type; Item : out Element_Type);
   procedure Write (File : in File_Type; Item : in Element_Type);

   function End_Of_File (File : in File_Type) return Boolean;

   --  Exceptions

   Status_Error : exception renames IO_Exceptions.Status_Error;
   Mode_Error   : exception renames IO_Exceptions.Mode_Error;
   Name_Error   : exception renames IO_Exceptions.Name_Error;
   Use_Error    : exception renames IO_Exceptions.Use_Error;
   Device_Error : exception renames IO_Exceptions.Device_Error;
   End_Error    : exception renames IO_Exceptions.End_Error;
   Data_Error   : exception renames IO_Exceptions.Data_Error;


   type File_Type is limited null record;

end Ada.Sequential_IO;

See also edit

Wikibook edit

External examples edit

Ada Reference Manual edit

Ada 95 edit

Ada 2005 edit

Ada 2012 edit

Open-Source Implementations edit