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.
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.
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);
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{
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).
If an external environment allows alternative specifications of the name
(for example, abbreviations), the string returned by the function should
correspond to a full specification of the name.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
Returns True if the file is open (that is,
if it is associated with an external file), otherwise returns False.
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.
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