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A.12.1 The Package Streams.Stream_IO

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The subprograms in the child package Streams.Stream_IO provide control over stream files. Access to a stream file is either sequential, via a call on Read or Write to transfer an array of stream elements, or positional (if supported by the implementation for the given file), by specifying a relative index for an element. Since a stream file can be converted to a Stream_Access value, calling stream-oriented attribute subprograms of different element types with the same Stream_Access value provides heterogeneous input-output. See 13.13 for a general discussion of streams. 

Static Semantics

1.1/1
 The elements of a stream file are stream elements. If positioning is supported for the specified external file, a current index and current size are maintained for the file as described in A.8. If positioning is not supported, a current index is not maintained, and the current size is implementation defined.
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The library package Streams.Stream_IO has the following declaration: 
3/3
with Ada.IO_Exceptions;
package Ada.Streams.Stream_IO is
    pragma Preelaborate(Stream_IO);
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    type Stream_Access is access all Root_Stream_Type'Class;
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    type File_Type is limited private;
    pragma Preelaborable_Initialization(File_Type);
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    type File_Mode is (In_File, Out_File, Append_File);
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    type    Count          is range 0 .. implementation-defined;
    subtype Positive_Count is Count range 1 .. Count'Last;
      -- Index into file, in stream elements.
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    procedure Create (File : in out File_Type;
                      Mode : in File_Mode := Out_File;
                      Name : in String    := "";
                      Form : in String    := "");
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    procedure Open (File : in out File_Type;
                    Mode : in File_Mode;
                    Name : in String;
                    Form : in String := "");
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    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);
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    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;
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    function Is_Open     (File : in File_Type) return Boolean;
    function End_Of_File (File : in File_Type) return Boolean;
13
    function Stream (File : in File_Type) return Stream_Access;
        -- Return stream access for use with T'Input and T'Output
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    -- Read array of stream elements from file
    procedure Read (File : in  File_Type;
                    Item : out Stream_Element_Array;
                    Last : out Stream_Element_Offset;
                    From : in  Positive_Count);
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    procedure Read (File : in  File_Type;
                    Item : out Stream_Element_Array;
                    Last : out Stream_Element_Offset);
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    -- Write array of stream elements into file
    procedure Write (File : in File_Type;
                     Item : in Stream_Element_Array;
                     To   : in Positive_Count);
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    procedure Write (File : in File_Type;
                     Item : in Stream_Element_Array);
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    -- Operations on position within file
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    procedure Set_Index(File : in File_Type; To : in Positive_Count);
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    function Index(File : in File_Type) return Positive_Count;
    function Size (File : in File_Type) return Count;
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    procedure Set_Mode(File : in out File_Type; Mode : in File_Mode);
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    procedure Flush(File : in File_Type);
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    -- 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;
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private
   ... -- not specified by the language
end Ada.Streams.Stream_IO;
27.1/2
  The type File_Type needs finalization (see 7.6).
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The subprograms given in subclause A.8.2 for the control of external files (Create, Open, Close, Delete, Reset, Mode, Name, Form, Is_Open, and Flush) are available for stream files.
28.1/2
  The End_Of_File function:
28.2/2
Propagates Mode_Error if the mode of the file is not In_File;
28.3/3
If positioning is supported for the given external file, the function returns True if the current index exceeds the size of the external file; otherwise, it returns False;
28.4/3
If positioning is not supported for the given external file, the function returns True if no more elements can be read from the given file; otherwise, it returns False. 
28.5/2
  The Set_Mode procedure sets the mode of the file. If the new mode is Append_File, the file is positioned to its end; otherwise, the position in the file is unchanged.
28.6/4
  This paragraph was deleted.
29/1
The Stream function returns a Stream_Access result from a File_Type object, thus allowing the stream-oriented attributes Read, Write, Input, and Output to be used on the same file for multiple types. Stream propagates Status_Error if File is not open.
30/2
The procedures Read and Write are equivalent to the corresponding operations in the package Streams. Read propagates Mode_Error if the mode of File is not In_File. Write propagates Mode_Error if the mode of File is not Out_File or Append_File. The Read procedure with a Positive_Count parameter starts reading at the specified index. The Write procedure with a Positive_Count parameter starts writing at the specified index. For a file that supports positioning, Read without a Positive_Count parameter starts reading at the current index, and Write without a Positive_Count parameter starts writing at the current index.
30.1/1
  The Size function returns the current size of the file.
31/1
The Index function returns the current index. 
32
The Set_Index procedure sets the current index to the specified value.
32.1/1
  If positioning is supported for the external file, the current index is maintained as follows:
32.2/1
For Open and Create, if the Mode parameter is Append_File, the current index is set to the current size of the file plus one; otherwise, the current index is set to one.
32.3/1
For Reset, if the Mode parameter is Append_File, or no Mode parameter is given and the current mode is Append_File, the current index is set to the current size of the file plus one; otherwise, the current index is set to one.
32.4/1
For Set_Mode, if the new mode is Append_File, the current index is set to current size plus one; otherwise, the current index is unchanged.
32.5/1
For Read and Write without a Positive_Count parameter, the current index is incremented by the number of stream elements read or written.
32.6/1
For Read and Write with a Positive_Count parameter, the value of the current index is set to the value of the Positive_Count parameter plus the number of stream elements read or written. 
33
If positioning is not supported for the given file, then a call of Index or Set_Index propagates Use_Error. Similarly, a call of Read or Write with a Positive_Count parameter propagates Use_Error.
Paragraphs 34 through 36 were deleted. 

Erroneous Execution

36.1/1
  If the File_Type object passed to the Stream function is later closed or finalized, and the stream-oriented attributes are subsequently called (explicitly or implicitly) on the Stream_Access value returned by Stream, execution is erroneous. This rule applies even if the File_Type object was opened again after it had been closed. 
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