The SIMULA FILE classes

Simula contains a hierarchy of files for both formatted and un-formatted I/O:

Note that all files share a common ancestor in the prefix hierarchy: "file". You can also create your own sub-classes of these files for further specialization.

Standard Input and Output

The two file objects Sysin (Infile) and Sysout (Printfile) are always connected to the standard input and output channel, respectively. A user program acts as if it were enclosed in the following inspect statements:

      inspect Sysin do
         inspect Sysout do
            <... user program ...>

In a program, all unqualified calls to Inimage, Inint etc will refer to Sysin (stdin) and all calls to Outimage, Outint etc to Sysout (stdout). stdin and stdout can be redirected in MPW in the customary fashion (< or >).

Note that some name clashes occur: an unqualified reference to Image, Pos, SetPos, Length or More will refer to Sysout, due to the ordering of the inspect's. If you wish to access Sysin's image (pos, ...) you write Sysin.Image (Sysin.Pos, ...)

Class FILE

    class file(FILENAME); value FILENAME; text FILENAME;
    begin
          Boolean OPEN; ! true if the file is open ;
    
          text    procedure Filename; Filename:-copy(FILENAME);
          Boolean procedure Isopen;   isopen  :=OPEN;
          Boolean procedure Setaccess(mode);text mode ; ......;
    
          if filename==Notext then error("...");
          
    end --- File --- ;

Class Imagefile

    File class Imagefile;
	begin
	   text Image;   ! -- the record buffer, created at "Open";
	   procedure SetPos(i); integer i; 
	      Image.SetPos(i);
	   integer procedure Pos;
	      Pos := Image.Pos;
	   Boolean procedure More;
	      More := Image.More;
	   integer procedure Length;
	      Length := Image.Length;
	end;

Class Infile

    Imagefile class Infile;
	begin
	   Boolean procedure Open(FileImage); text FileImage; ...;
	   Boolean procedure Close; ...;
	   
	           procedure Inimage; ...; ! -- reads the next input record --> Image;
	   Boolean procedure inRecord; ...;
	   
	   Boolean procedure Endfile; ...;  ! -- true if endfile has been read;
	   
	   character procedure Inchar; ...;  
	   		! -- gets the next character from Image;
	   Boolean procedure Lastitem; ...;  
	   		! -- skips blanks and tabs, true if Endfile;
	   text procedure Intext(N); integer N;
			! -- a copy of the next N characters from Image;
	   integer procedure Inint;  
	   		! -- skips blanks and tabs, reads next 	integer;
	   long real procedure Inreal;  ! -- skips, reads next real;
	end;

Attributes of INFILE

Class Outfile

    File class Outfile;
	begin
	   Boolean procedure Open(Fileimage); text Fileimage; ...;
	   Boolean procedure Close; ...;
	   
	   procedure Outimage; ...;
	   procedure BreakOutimage; ...;
	   procedure OutRecord; ...;
	   
	   procedure Outchar(C); character C; ...;
	   procedure Outtext(T); text T; ...;
	   procedure Outint(Inum,Width); integer Inum,Width; ...;
	   procedure Outfix(Rnum,Ndec,Width); (long) real Rnum; 
	   		integer 	Ndec,Width; ...;
	   procedure Outreal(Rnum,Ndec,Width); (long) real Rnum; 
	   		integer 	Ndec,Width; ...;
	end;

Attributes of Outfile

Note:

since Intext/Outtext call Inbyte/Outbyte, also these routines will increment the ordinal number.

Class Printfile

Outfile class Printfile;
begin
   Boolean procedure Open(Fileimage); text Fileimage; ...;
   Boolean procedure Close; ...;
   integer procedure Line;  ! -- return number of current line 
                                     (relative to page start);
   integer procedure Page;  ! -- return current page number;
   integer procedure LinesPerPage(N); integer N; ...; 
                                  ! -- set page size to N lines, return 
                                    -- previous value;
   procedure Spacing(N); integer N; ...;  
                                  ! -- set line distance to N (default 1);
   procedure Eject(N); ...; integer N;  
                                  ! -- position to line N, Eject(1) gives new page;
   procedure Outimage; ...; ! -- as in Outfile but increments line (& page) number;
   procedure Outrecord;...; ! -- analogous;
end;

Open & Close

Example (copy the file "in" to "out"):

	ref(Infile) Input; 
	ref(Outfile) Output;
	Input :- new Infile("in");  
	if not Input.Open(Blanks(132)) then 
	   Error("Input file does not exist"); 
	Output :- new Outfile("out"); 
	Output.Open(Blanks(132));
	Input.Inimage;
	while not Input.Endfile do
	begin
	   Output.Image := Input.Image;
	   Output.Outimage; Input.Inimage;
	end;
	Input.Close; Output.Close;

Open the output file in this way:
    Output.Open(INPUT.IMAGE);
    
then copy:
    while not Input.Endfile do
    begin
        Output.Outimage;  ! same buffer!;
        Input.Inimage;
    end;

Class DirectFile

	Imagefile class Directfile;
	begin
	   integer procedure Location; ...;  ! -- current record number;
	   procedure Locate(N); integer N; ...;  
	   		! -- set current record number 	to N;
	   integer procedure LastLoc; ...;  
	   		! -- highest record number written;
	   integer procedure MaxLoc; ...;  
	   		! -- highest permissible record 	number;
	   Boolean procedure DeleteImage;  ! -- delete current record;
	end;

Attributes of DirectFile

NOTE: The input routines (Inchar, Inint etc.) in directfiles skips all unwritten records.

DirectFile Class KeyFile

A KeyFile allows access by KEY to variable length records.

KeyFiles are not part of the Standard SIMULA language. They are a Montreal addition defined by the external CLASS Keyfile (which uses the "textUtil CLASS). These are available under the "-diro" SIM compiler option.

	Directfile class KeyFile( HashSize ); integer HashSize;
	begin
	   Procedure CLOSE; ... ;
	   Text Procedure READ  ( Key );       Text Key  ;
	   Procedure      WRITE ( Key, Data ); Text Key, Data  ;
	   Procedure      DELETE( Key );       Text Key;
	end;

Notes:

• Keys are separated from the rest of a record by the character "|". You must take care not to use this character within keys.
• Access to records is done via a hashtable and all records whose keys hash to the same value are kept in a list in the OVERFLOW area.
• Records too large to fit in one physical record are divided into fixed size chunks and kept as lists also in the overFlow area.

KeyFiles are made up of three parts:

1. Record 1 keeps global information on the file (hashSize and address of first record on FREELIST)
2. A hasharea of fixed size (determined at creation).
3. An OVERFLOW area where synonyms and record continuations are kept

Attributes of KeyFile

	begin
		external class keyfile;
		external class textutil;
		
		ref(KeyFile) F;
		integer i;
		Text Key, data;
		
		F :- new KeyFile("t1.60",10);
		for i := 1 step 1 until 10 do 
		begin
			Key :- int_as_text(i);
			F.WRITE(Key,"Contenu de l'enregistrement.....");
		end;
		 
		F.DELETE( int_as_text(3) );
		
		for i := 1 step 1 until 10 do 
		begin
			Key :- int_as_text(i);
			data :- F.READ(Key);
			outint(i,3); outtext(Key & ": " & data); outimage;
		end;
		
		F.CLOSE;
	end

Bytefile

class Bytefile;
begin
   short integer procedure ByteSize; ...;  ! -- returns 8;
end;

Inbytefile

Bytefile class Inbytefile;
begin
   Boolean procedure Open; ...;  ! -- note that the byte buffer is internal to the file;
   Boolean procedure Close; ...;
   Boolean procedure Endfile; ...;  ! -- true if there are no more bytes to read;
   short integer procedure Inbyte; ...;  ! -- the ASCII number of the input byte, sets
                                                                       -- Endfile and returns 0 if no more bytes;
   text procedure Intext(T); text T;
   begin   ! -- fills the frame of the text T with successive input bytes;
      T.Setpos(1);
      while T.More and not Endfile do T.Putchar(Char(Inbyte);
       if Endfile then T.Setpos(T.Pos-1);
       Intext :- T.Sub(1,T.Pos-1);
   end;
end;

Outbytefile

Bytefile class Outbytefile;
begin
   Boolean procedure Open; ...;  ! -- note that the byte buffer is internal to the file;
   Boolean procedure Close; ...;
   procedure Outbyte(X); short integer X; ...;  ! -- writes a byte X;
   procedure Outtext(T); text T;
   begin   ! -- outputs all the characters in T as bytes;
      T.Setpos(1);
      while T.More do
          Outbyte(Rank(T.Getchar));
    end;
end;

Directbytefile

Bytefile class Directbytefile;
begin
   integer procedure Location; ...;  ! -- current byte number;
   procedure Locate(N); integer N; ...;  ! -- set current byte number to N;
   integer procedure LastLoc; ...;  ! -- highest byte number written;
   integer procedure MaxLoc; ...;  ! -- highest permissible byte number;
end;

Attributes of Directbytefile

Note:

since Intext/Outtext call Inbyte/Outbyte, also these routines will increment the ordinal number.

SetAccess

Boolean procedure Setaccess(Mode); text Mode; ...;

(NA = Not Applicable)

Setaccess example

Open a directfile: use existing file if it already exists, create it if it does not.

	
	ref(Directfile) DF;
	Outtext("Enter file name: "); BreakOutimage;
	Inimage;
	DF :- new Directfile(Sysin.Image.Strip);
	DF.Setaccess("AnyCreate");
	if not DF.Open(Blanks(30)) then
	   Error("Could not open " & DF.Filename);

Cause a temporary file to be deleted after use:

	inspect new Directbytefile("temp") do
	begin
	   Open;
	   ...;
	   Setaccess("Purge");
	   Close;
	end;

Create mode

Purge mode

Append mode

Readwrite mode