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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.
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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.2
The library package Streams.Stream_IO has the following declaration:
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with Ada.IO_Exceptions;package Ada.Streams.Stream_IO is
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type Stream_Access is access all Root_Stream_Type'Class;
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type File_Type is limited private;
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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;
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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;
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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, and Is_Open) are available for stream files.
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The End_Of_File function:
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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.
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The Flush procedure synchronizes the external file with the internal file (by flushing any internal buffers) without closing the file or changing the position. Mode_Error is propagated if the mode of the file is In_File.
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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.
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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.
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The Size function returns the current size of the file.
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The Index function returns the current index.
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The Set_Index procedure sets the current index to the specified value.
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If positioning is supported for the external file, the current index is maintained as follows:
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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.
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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.