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Mystic Pascal User Manual 59
9. Input/Output
Mystic Pascal supports all standard Pascal I/O procedures
and functions and has extensions to support random disk file
access and to assign a DOS file name to a Pascal file variable.
+ ASSIGN associate a file name with a file variable
+ CLOSE terminate processing on a file
EOF Boolean function indicates end-of-file
condition
EOLN Boolean function indicates end-of-line
condition for text files
1.6 GET move file pointer to next component
+ IORESULT integer function status of I/O operation
PAGE advance textfile output to new page
1.6 PUT append buffer variable to file
READ obtain input from console or disk file
READLN obtain textfile input from new line
RESET prepare an existing file for input
REWRITE create a file for output
+ SEEK position the file pointer for random access
WRITE output data to console, printer, disk file
WRITELN output textfile data and terminate line
Section 9: Input/Output
Mystic Pascal User Manual 60
9.1 File Variables
File variables, like other variables, are declared in a VAR
section. They indicated the data type of the file's components.
TYPE
DATAFILE = FILE OF REAL;
VAR
F1 : DATAFILE;
F2 : FILE OF ARRAY [0..63] OF CHAR;
F3 : TEXT;
Textfiles are declared by the predefined type TEXT.
Textfiles consist of lines of characters separated by the end-of-
line byte sequence 0DH, 0AH (carriage return, line feed).
9.2 Standard Files
The DOS operating system supports several standard "files"
or logical devices which are always available. These may be used
directly as file variables in Read/ln and Write/ln. They may
also be assigned to Pascal file variables by the Assign
procedure.
CON standard console device (input/output)
KBD keyboard device (input without echoing)
AUX auxiliary device (input/output)
LST printer (output)
PRN printer (output)
If no file variable is specified as the first parameter in
the Read/ln or Write/ln procedures, the default files INPUT and
OUTPUT respectively are used. These are assigned to the standard
console and keyboard devices.
9.3 How to Send Data to Your Printer
To route output to your printer specify the Standard File
LST or PRN in your WRITE or WRITELN statements.
WRITELN( PRN, 'This line will be printed.');
WRITE( PRN, 'X =',X,' Y =',Y,' Z =',Z );
Section 9: Input/Output
Mystic Pascal User Manual 61
9.4 ASSIGN (Non-Standard Feature)
ASSIGN( Filvar, String )
ASSIGN( Filvar, Standard_file )
The procedure Assign is used to associate a file variable
with a particular disk file or standard file.
The ability to assign standard files to a file variable
allows complete I/O redirection within a Pascal program. For
example, a program which creates reports could route its output
to a disk file one time and to a printer or console another time.
There is no need for separate WRITE statements for each type of
output.
10: WRITELN('Select output device for Report Listing');
WRITELN('1 = Console 2 = Printer 3 = Diskfile');
READLN(X);
CASE X OF
1 : ASSIGN( REPORTFILE, CON );
2 : ASSIGN( REPORTFILE, PRN );
3 : ASSIGN( REPORTFILE, 'REPORT.LST' );
ELSE GOTO 10
END;
Section 9: Input/Output
Mystic Pascal User Manual 62
9.5 CLOSE (Non-Standard Feature)
CLOSE( Filvar )
The Close procedure must be called after completing
processing on a disk file to ensure that the disk directory is
updated. Failure to Close a file after updating it may result in
the loss of data.
Closing a file variable to which a standard file has been
assigned is treated as a null operation.
CLOSE( F1 );
CLOSE( REPORTFILE );
CLOSE( SORTFILE2 );
Section 9: Input/Output
Mystic Pascal User Manual 63
9.6 EOF
EOF( Filvar )
Eof is a Boolean function which indicates the end-of-file
condition. Eof is true only when the file pointer points past
the last component of the file, otherwise it is false.
{ Copy F1 into F2 }
WHILE NOT EOF( F1 ) DO
BEGIN
READ( F1, X );
WRITE( F2, X )
END
Section 9: Input/Output
Mystic Pascal User Manual 64
9.7 EOLN
EOLN
EOLN( Filvar )
Eoln is a Boolean function which indicates the end-of-line
condition of a textfile. If no file variable is specified, the
function assumes the file INPUT. It is a compiler error if the
file variable is not a textfile.
{ Average N numbers from the console }
SUM := 0; N := 0;
WHILE NOT EOLN DO
BEGIN
READ( X );
SUM := SUM + X;
N := N + 1
END
WRITELN( 'The average is', SUM DIV N );
Section 9: Input/Output
Mystic Pascal User Manual 65
9.8 GET, PUT and Buffer Variables ** 1.6 **
Standard Pascal supports Input/Output operations which are
more primitive than Read and Write. In fact Read and Write are
defined in terms of the procedures Get and Put, which only move
data between a file and its buffer variable.
A buffer variable is associated with each file. Its data
type is the same as the components of the file. A buffer
variable is accessed by using the file variable's name followed
by an uparrow.
WRITE( F, X ) is equivalent to F^ := X; PUT( F )
READ( F, X ) is equivalent to GET( F ); X := F^
GET( Filvar )
The Get procedure advances the file pointer to the next
component of the file. The current component is available in the
file's buffer variable.
PUT( Filvar )
The Put procedure appends the value in the buffer variable
to the file. The condition EOF( Filvar ) must be true when Put
is called.
Section 9: Input/Output
Mystic Pascal User Manual 66
9.9 IORESULT
IORESULT
This integer function gives the return code from the last
Input/Output operation. It should be checked after each RESET
and REWRITE to be sure that the operation completed successfully.
The IORESULT values are the same values returned by DOS.
0 Successful completion
1 Invalid function number
2 File not found
3 Path not found
4 Too many open files (no handles left)
5 Access denied
6 Invalid handle
7 Memory control blocks destroyed
8 Insufficient memory
9 Invalid memory block address
10 Invalid environment
11 Invalid format
12 Invalid access code
13 Invalid data
14 (not used)
15 Invalid drive was specified
16 Attempted to remove the current directory
17 Not same device
18 No more files
Section 9: Input/Output
Mystic Pascal User Manual 67
9.10 PAGE
PAGE
PAGE( Filvar )
The Page procedure causes the textfile to begin printing on
a new page if printed on a suitable device. If no file variable
is specified, the file OUTPUT is assumed. It is a compiler error
if the file variable is not a textfile. If the file contains a
partial line of text, an implicit Writeln is issued.
Page always outputs a form feed character CHR(12).
PAGE;
PAGE( REPORTFILE );
Section 9: Input/Output
Mystic Pascal User Manual 68
9.11 READ
READ( variable_list )
READ( Filvar, variable_list )
The Read procedure is used to obtain input from a disk file
or standard file such as the console keyboard. The input
value is stored directly into one or more variables. If no file
variable is specified, the INPUT file is assumed.
READ( X, Y, Z );
READ( F1, CUSTOMER );
FOR I := 1 TO 100 DO READ( F2, X[I] );
Section 9: Input/Output
Mystic Pascal User Manual 69
9.12 READLN
READLN
READLN( variable_list )
READLN( Filvar )
READLN( Filvar, variable_list )
The Readln procedure is similar to Read but may be applied
only to textfiles. After the Readln has been processed, the file
pointer is set to the beginning of the following text line.
Unused data on the current line is skipped over.
READLN; {Skip to next line of keyboard input}
READLN( DATAFILE, PARM1, PARM2, PARM3 ); {ignore parm4,5}
Section 9: Input/Output
Mystic Pascal User Manual 70
9.13 RESET
RESET( Filvar )
The Reset procedure is used to open an existing disk file
for input or output operations. An Assign procedure must have
been used before Reset to assign a disk file name or standard
file with the file variable. Reseting a file variable to which a
standard file has been assigned is treated as a null operation.
If a disk file is not found by Reset, a run-time error
occurs.
RESET( F2 );
RESET( DATAFILE );
RESET( TEXTFILE );
Section 9: Input/Output
Mystic Pascal User Manual 71
9.14 REWRITE
REWRITE( Filvar )
The Rewrite procedure is used to create a new disk file for
output and input. If a disk file with the same file name already
exists, it is deleted before the new file is created.
An Assign procedure must have been used before Rewrite to
assign a disk file name or standard file to the file variable.
Rewriting a file variable to which a standard file has been
assigned is treated as a null operation.
If the disk directory is full, a run-time error occurs.
REWRITE( F4 );
REWRITE( REPORTFILE );
REWRITE( DATAFILE );
Section 9: Input/Output
Mystic Pascal User Manual 72
9.15 SEEK (Non-Standard Feature)
SEEK( Filvar, N )
The Seek procedure positions the file pointer at the Nth
component of the file. The first component is number 0. It is a
compiler error if the file variable is a textfile.
Seek is used for random access file processing.
SEEK( F1, INDEX );
SEEK( DOSSIER, AGENTNUM );
Section 9: Input/Output
Mystic Pascal User Manual 73
9.16 WRITE
WRITE( variable_list )
WRITE( Filvar, variable_list )
The Write procedure is used to output data values to a
textfile or non-textfile. If no file variable is specified, the
OUTPUT file is assumed. If the file is a textfile then integers,
reals and Booleans are automatically converted to text format.
WRITE('Enter longitude, latitude of target : ');
WRITE( REPORTFILE, CHR(9), 'SALES SUMMARY FOR ',MONTH );
WRITE( MODEM, SIGNON );
Section 9: Input/Output
Mystic Pascal User Manual 74
9.17 WRITELN
WRITELN
WRITELN( variable_list )
WRITELN( Filvar )
WRITELN( Filvar, variable_list )
The Writeln procedure is similar to Write but may only be
applied to textfiles. After the variables on the list have been
output, a standard end-of-line byte sequence is output. This is
(carriage_return, line_feed) 13, 10.
PROCEDURE SKIP ( X : INTEGER );
VAR I : INTEGER;
BEGIN
IF (X > 0) AND (X <= 60) THEN
FOR I := 1 TO X DO WRITELN
END;
WRITELN( F1 );
WRITELN( F1, X, Y, Z );
Section 9: Input/Output
