Closing Files

When your program closes a file, it breaks the association between the logical file and the physical file; therefore, it cannot access the file or file buffer variable. It must reopen the file before attempting to operate on it in any other way, or it is a run-time error. One way to close a file is with the predefined procedure close. A call to close has the following syntax and parameters.

Syntax

close (logical_file [, close_option])

Parameters

logical_file

The name of the logical file to be closed.

close_option

A string or PAC expression whose value is one of the following:

SAVE or LOCK: The file is saved permanently.
TEMP or NORMAL: The file is saved temporarily. What happens to the temporary file when the current session or job ends is system-dependent. For the MPE/iX operating system, see Appendix A “MPE/iX Dependencies ”; for HP-UX, see Appendix B “HP-UX Dependencies ”.
CRUNCH: The effect of this option on the space after the end-of-file marker is system-dependent. See Appendix A “MPE/iX Dependencies ” (MPE/iX) or Appendix B “HP-UX Dependencies ” (HP-UX).
PURGE: The file is removed.

A program also closes a logical file and its associated physical file when the program:

Terminates.
Exits the routine that declares the file, either because the routine ends, because it executes a goto statement that transfers control to a routine outside its scope, or it calls the predefined procedure escape because of a run-time error Chapter 11 “Error Recovery and Debugging ” explains escape).
Reopens the file (in which case the file is closed before it is reopened).

Also, a program closes a file that is stored on the heap when it deallocates the file's heap space by calling the predefined procedure dispose or release with the appropriate parameter (see Chapter 6 “Dynamic Variables ”).

A program closes a pre-existing physical file (one that it did not create) in the same state that it was in before the program opened it. If a program creates a file, however, it can specify the state in which the close procedure closes it.

Example

PROGRAM prog;
 
LABEL
   9999;
 
TYPE
   ftype = FILE OF integer;
 
VAR
   f1 : ftype;
 
PROCEDURE p;
VAR
   f2 : ftype;
BEGIN
   reset(f2);  {Opens f2}
   goto 9999;  {Closes f2 and f3}
END;
 
PROCEDURE q;
VAR
   f3 : ftype;
BEGIN
   open(f3);  {Opens f3}
   p;
   {p never returns here}
END;
 
BEGIN
   rewrite(f1);       {Opens f1}
   q;
   9999 : reset(f1);  {Closes and reopens f1}
   close(f1);         {Closes f1}
END.

Closing Files

Technical documentation

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