FileSystem.md

FileSystem

Basic character-level file I/O with an opaque File handle. This is the PIM4 standard file module -- it reads and writes one character at a time. For reading/writing raw bytes, blocks of data, or seeking within a file, use BinaryIO instead.

Available in PIM4 mode (the default). No special flags needed.

Types

Type	Description
File	Opaque file handle (internally an ADDRESS). Created by Lookup, released by Close.

Variables

Variable	Type	Description
Done	BOOLEAN	Set after every operation. TRUE if it succeeded, FALSE on error (file not found, EOF, etc.).

Procedures

PROCEDURE Lookup(VAR f: File; name: ARRAY OF CHAR; newFile: BOOLEAN);

Open a file by name. If newFile is TRUE and the file does not exist, it is created. If newFile is FALSE and the file does not exist, Done is set to FALSE. On success, f receives a valid file handle.

The parameter name newFile is a PIM4 convention meaning "create if absent" -- it does not mean "always create a new file".

PROCEDURE Close(VAR f: File);

Close the file and release the handle. After this call, f should not be used.

PROCEDURE ReadChar(VAR f: File; VAR ch: CHAR);

Read the next character from the file into ch. At end-of-file, Done is set to FALSE.

PROCEDURE WriteChar(VAR f: File; ch: CHAR);

Write one character to the file.

Example

MODULE FileDemo;
FROM InOut IMPORT WriteString, WriteLn;
FROM FileSystem IMPORT File, Lookup, Close, ReadChar, WriteChar, Done;

VAR
  f: File;
  ch: CHAR;

BEGIN
  (* Write a file *)
  Lookup(f, "test.txt", TRUE);
  IF Done THEN
    WriteChar(f, 'H');
    WriteChar(f, 'i');
    Close(f)
  END;

  (* Read it back *)
  Lookup(f, "test.txt", FALSE);
  IF Done THEN
    LOOP
      ReadChar(f, ch);
      IF NOT Done THEN EXIT END;
      InOut.Write(ch)
    END;
    Close(f);
    WriteLn
  END
END FileDemo.