A.8.2 File Management
Static Semantics
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
A.10.2.
procedure Create(File : in out File_Type;
Mode : in File_Mode := default_mode;
Name : in String := "";
Form : in String := "");
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.
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.
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.
procedure Open(File : in out File_Type;
Mode : in File_Mode;
Name : in String;
Form : in String := "");
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.
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.
procedure Close(File : in out File_Type);
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.
The exception Status_Error
is propagated if the given file is not open.
procedure Delete(File : in out File_Type);
Deletes the external file associated with the
given file. The given file is closed, and the external file ceases to
exist.
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.
procedure Reset(File : in out File_Type; Mode : in File_Mode);
procedure Reset(File : in out File_Type);
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.
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.
function Mode(File : in File_Type) return File_Mode;
Returns the current mode of the given file.
The exception Status_Error
is propagated if the file is not open.
function Name(File : in File_Type) return String;
Returns a string which uniquely identifies the
external file currently associated with the given file (and may thus
be used in an Open operation).
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.
function Form(File : in File_Type) return String;
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).
The exception Status_Error
is propagated if the given file is not open.
function Is_Open(File : in File_Type) return Boolean;
Returns True if the file is open (that is, if
it is associated with an external file); otherwise, returns False.
procedure Flush(File : in File_Type);
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.
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.
The nested package Wide_File_Names provides operations
equivalent to the operations of the same name of the outer package except
that Wide_String is used instead of String for the name and form of the
external file.
The nested package Wide_Wide_File_Names provides
operations equivalent to the operations of the same name of the outer
package except that Wide_Wide_String is used instead of String for the
name and form of the external file.
Implementation Permissions
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.
Ada 2005 and 2012 Editions sponsored in part by Ada-Europe
