Contents Index Search Previous Next
A.10.2 Text File Management
Static Semantics
1
The only allowed
file modes for text files are the modes In_File, Out_File, and Append_File.
The subprograms given in subclause
A.8.2
for the control of external files, and the function End_Of_File given
in subclause
A.8.3 for sequential input-output,
are also available for text files. There is also a version of End_Of_File
that refers to the current default input file. For text files, the procedures
have the following additional effects:
2
- For the procedures Create and Open:
After a file with mode Out_File or Append_File is opened, the page length
and line length are unbounded (both have the conventional value zero).
After a file (of any mode) is opened, the current column, current line,
and current page numbers are set to one. If the mode is Append_File,
it is implementation defined whether a page terminator will separate
preexisting text in the file from the new text to be written.
2.a
Reason: For a file with
mode Append_File, although it may seem more sensible for Open to set
the current column, line, and page number based on the number of pages
in the file, the number of lines on the last page, and the number of
columns in the last line, we rejected this approach because of implementation
costs; it would require the implementation to scan the file before doing
the append, or to do processing that would be equivalent in effect.
2.b
For similar reasons, there is
no requirement to erase the last page terminator of the file, nor to
insert an explicit page terminator in the case when the final page terminator
of a file is represented implicitly by the implementation.
3
- For the procedure Close: If the file
has the current mode Out_File or Append_File, has the effect of calling
New_Page, unless the current page is already terminated; then outputs
a file terminator.
4
- For the procedure Reset: If the file
has the current mode Out_File or Append_File, has the effect of calling
New_Page, unless the current page is already terminated; then outputs
a file terminator. The current column, line, and page numbers are set
to one, and the line and page lengths to Unbounded. If the new mode is
Append_File, it is implementation defined whether a page terminator will
separate preexisting text in the file from the new text to be written.
4.a
Reason: The behavior
of Reset should be similar to closing a file and reopening it with the
given mode
5
The exception Mode_Error is propagated by the
procedure Reset upon an attempt to change the mode of a file that is
the current default input file, the current default output file, or the
current default error file.
6
22 An
implementation can define the Form parameter of Create and Open to control
effects including the following:
7
- the interpretation
of line and column numbers for an interactive file, and
8
- the interpretation
of text formats in a file created by a foreign program.
Contents Index Search Previous Next Legal