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A.8.2 File Management

Static Semantics

1
The procedures and functions described in this subclause provide for the control of external files; their declarations are repeated in each of the packages for sequential, direct, text, and stream input-output. For text input-output, the procedures Create, Open, and Reset have additional effects described in subclause A.10.2
2
procedure Create(File : in out File_Type;
                 Mode : in File_Mode := default_mode;
                 Name : in String := "";
                 Form : in String := "");
3/2
{AI95-00283-01} Establishes a new external file, with the given name and form, and associates this external file with the given file. The given file is left open. The current mode of the given file is set to the given access mode. The default access mode is the mode Out_File for sequential, stream, and text input-output; it is the mode Inout_File for direct input-output. For direct access, the size of the created file is implementation defined.
3.a/4
Ramification: {AI12-0005-1} For a direct file, the initial value of current index is 1 (see A.8). 
4
A null string for Name specifies an external file that is not accessible after the completion of the main program (a temporary file). A null string for Form specifies the use of the default options of the implementation for the external file.
5
The exception Status_Error is propagated if the given file is already open. The exception Name_Error is propagated if the string given as Name does not allow the identification of an external file. The exception Use_Error is propagated if, for the specified mode, the external environment does not support creation of an external file with the given name (in the absence of Name_Error) and form.
6
procedure Open(File : in out File_Type;
               Mode : in File_Mode;
               Name : in String;
               Form : in String := "");
7
Associates the given file with an existing external file having the given name and form, and sets the current mode of the given file to the given mode. The given file is left open.
7.a/4
Ramification: {AI12-0005-1} For a direct file, the initial value of current index is 1 (see A.8). 
8
The exception Status_Error is propagated if the given file is already open. The exception Name_Error is propagated if the string given as Name does not allow the identification of an external file; in particular, this exception is propagated if no external file with the given name exists. The exception Use_Error is propagated if, for the specified mode, the external environment does not support opening for an external file with the given name (in the absence of Name_Error) and form.
9
procedure Close(File : in out File_Type);
10
Severs the association between the given file and its associated external file. The given file is left closed. In addition, for sequential files, if the file being closed has mode Out_File or Append_File, then the last element written since the most recent open or reset is the last element that can be read from the file. If no elements have been written and the file mode is Out_File, then the closed file is empty. If no elements have been written and the file mode is Append_File, then the closed file is unchanged.
11
The exception Status_Error is propagated if the given file is not open.
12
procedure Delete(File : in out File_Type);
13
Deletes the external file associated with the given file. The given file is closed, and the external file ceases to exist.
14
The exception Status_Error is propagated if the given file is not open. The exception Use_Error is propagated if deletion of the external file is not supported by the external environment.
15
procedure Reset(File : in out File_Type; Mode : in File_Mode);
procedure Reset(File : in out File_Type);
16/2
{AI95-00085-01} Resets the given file so that reading from its elements can be restarted from the beginning of the external file (for modes In_File and Inout_File), and so that writing to its elements can be restarted at the beginning of the external file (for modes Out_File and Inout_File) or after the last element of the external file (for mode Append_File). In particular, for direct access this means that the current index is set to one. If a Mode parameter is supplied, the current mode of the given file is set to the given mode. In addition, for sequential files, if the given file has mode Out_File or Append_File when Reset is called, the last element written since the most recent open or reset is the last element that can be read from the external file. If no elements have been written and the file mode is Out_File, the reset file is empty. If no elements have been written and the file mode is Append_File, then the reset file is unchanged.
17
The exception Status_Error is propagated if the file is not open. The exception Use_Error is propagated if the external environment does not support resetting for the external file and, also, if the external environment does not support resetting to the specified mode for the external file.
18
function Mode(File : in File_Type) return File_Mode;
19
Returns the current mode of the given file.
20
The exception Status_Error is propagated if the file is not open.
21
function Name(File : in File_Type) return String;
22/2
{AI95-00248-01} Returns a string which uniquely identifies the external file currently associated with the given file (and may thus be used in an Open operation).
22.a/2
Discussion: {AI95-00248-01} Retrieving the full path can be accomplished by passing the result of Name to Directories.Full_Name (see A.16). It is important to drop the requirement on Name, as the only way to accomplish this requirement given that the current directory can be changed with package Directories is to store the full path when the file is opened. That's expensive, and it's better for users that need the full path to explicitly request it. 
23
The exception Status_Error is propagated if the given file is not open. The exception Use_Error is propagated if the associated external file is a temporary file that cannot be opened by any name.
24
function Form(File : in File_Type) return String;
25
Returns the form string for the external file currently associated with the given file. If an external environment allows alternative specifications of the form (for example, abbreviations using default options), the string returned by the function should correspond to a full specification (that is, it should indicate explicitly all options selected, including default options).
26
The exception Status_Error is propagated if the given file is not open.
27
function Is_Open(File : in File_Type) return Boolean;
28/3
{AI05-0264-1} Returns True if the file is open (that is, if it is associated with an external file); otherwise, returns False.
28.1/4
{AI12-0130-1} procedure Flush(File : in File_Type);
28.2/4
The Flush procedure synchronizes the external file with the internal file (by flushing any internal buffers) without closing the file. For a direct file, the current index is unchanged; for a stream file (see A.12.1), the current position is unchanged.
28.3/4
The exception Status_Error is propagated if the file is not open. The exception Mode_Error is propagated if the mode of the file is In_File.

Implementation Permissions

29
An implementation may propagate Name_Error or Use_Error if an attempt is made to use an I/O feature that cannot be supported by the implementation due to limitations in the external environment. Any such restriction should be documented. 

Wording Changes from Ada 95

29.a/2
{AI95-00085-01} Clarified that Reset affects and depends on the external file.
29.b/2
{AI95-00248-01} Removed the requirement for Name to return a full path; this is now accomplished by Directories.Full_Name(Name(File)) (see A.16). This is not documented as an inconsistency, because there is no requirement for implementations to change — the Ada 95 behavior is still allowed, it just is no longer required.
29.c/2
{AI95-00283-01} Added text to specify the default mode for a stream file. 

Wording Changes from Ada 2012

29.d/4
{AI12-0130-1} Procedure Flush is now defined here, so it can be used for all of the I/O packages. 

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