Power-Programmierung/CD1.mdf/pascal/compiler/mystic/pas6.doc

Text File | 1986-02-27 | 15.5 KB | 914 lines

        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