ftp.barnyard.co.uk/2015.02.ftp.barnyard.co.uk.tar/ftp.barnyard.co.uk/cpm/walnut-creek-CDROM/CPM/MSOFT/MSFTNW-1.APR

Text File | 2000-06-30 | 9KB | 179 lines

                      MICROSOFT NEWSLETTER

                           APRIL, 1982

                ================================

                         16 BIT PRODUCTS
                         ---------------

  There appears to be some confusion about our 16 bit products.
I hope this will explain our current policies and procedures.
  First, at this time, *NONE* of our 16 bit products (8086, 8088,
Z8000, 68000) are available as Microsoft Corporation End User
Products.  Instead, these products (MS-DOS, Xenix, Fortran,
Cobol, Pascal, etc) are licensed to a number of commercial
customers who then market them in conjunction with their own
hardware and/or systems.  We often refer to these customers as
"OEMs".   Since the marketing of a product licensed in this
manner is strictly up to the OEM, we cannot answer any questions
regarding the availability (or price) of these products.  In
addition, since the product may have been modified for the
specific hardware involved, we cannot answer any questions
regarding a particular implementation.
  In summary, our 16 bit products are "custom" products; for
information regarding these products, one should contact a
particular OEM, and NOT Microsoft.

      FILE ACCESS (CONT'D)
      --------------------
  Last issue we talked a bit about files, and the way CP/M
allocates file space on disk. This issue, let's look at
sequential file access as performed by MBasic/Bascom, Fortran and
Cobol.
  First, a quick review.  A sequential file is a file that is
accessed in sequence.  This "sequence" is the order in which the
records were entered.  If we write a file that contains 100
records;  and then attempt to read that file, if we want the 98th
record, we first have to read past records 1 thru 97. There is no
way to access a record "out of sequence" or randomly.  Usually,
if we want to update a sequential file, we read the old file as
input and write a new file containing the changed information.
  Now let's look at how each language handles sequential files.

  MBASIC/BASCOM
  The commands Basic uses for sequential I/O include OPEN, CLOSE,
LINE INPUT#, INPUT#, PRINT#, and WRITE#, and PRINT# USING.  When
we OPEN a sequential file in Basic, it must be OPENed as either
an input (I) or output (O) file.
  A file is then written by using a PRINT or WRITE statement for
each record you wish to write.  For example, the following code
segment opens a file, and writes 100 records to the file:
     OPEN "O",1,"TEST.DAT"
     FOR I= 1 TO 100
     J = I + I
     PRINT #1,"RECORD # ";I;J
     NEXT I
     CLOSE
  Note that we wrote both a string variable and a numeric
variable.  The resulting file will look something like this:
 RECORD # 1  2
 RECORD # 2  4
 ...
  The file will contain 100 records and each record will be
terminated with a carriage return/line feed pair.  The file
itself is terminated with a control-Z (Hexadecimal 1A).
  In the example above, we used the PRINT statement.  If we had
used the WRITE statement, the string would have been placed in
quotes, and there would have been a comma between the values of I
and J.  This is particularly useful when we attempt to read the
file again, as we'll see below.  PRINT# USING will produce
formatted output to a file, just a PRINT USING produces formatted
output to your terminal.
  Just as we have the WRITE and PRINT statements for output, we
have two corresponding statements for input:  LINE INPUT, and
INPUT.  The difference is the manner in which data is delimited.
LINE INPUT will read an entire record, up to (but not including)
the CR/LF (carriage return/line feed) pair.  This allows us to
input entire strings of data at one time. The INPUT statement
expects each numeric data item to be delimited by commas, and
strings contained in quotes.
  On input, the end of a file is detected by the EOF function, as
illustrated below:
     WHILE NOT E0F(1)
     .
     .
     WEND
  Here, we're checking file number 1 for end of file.
  To summarize, the file I/O statements in Basic format output
just as they would to the screen or printer.  The WRITE statement
writes a file that can be read easily with the INPUT statement;
and PRINT will generate data readable by the LINE INPUT
statement.

  FORTRAN
  Like Basic, FORTRAN uses the same I/O statements for sequential
disk files as it does for I/O to the console. However, in FORTRAN
we have a few extensions.  First, we can make use of UNFORMATTED
I/O to and from disk.  We also have access to the END= branch in
the READ statement, and the ERR= branch in the READ and WRITE
statements.  Finally, one should remember that FORTRAN limits
disk records to 128 characters of less.
  Let's look at formatted I/O first.  Sequential disk I/O in
FORTRAN is performed in the same manner as console I/O, with one
important difference.  When FORTRAN reads or writes a disk
record, the record is terminated with a carriage return ONLY (no
line feed).  Similarly, when FORTRAN reads a disk file, it
assumes that the records are terminated with only a carriage
return, and the line feed is treated as data.
  This idiosyncrasy can be annoying, but is fairly easy to deal
with.  On input, we can simply skip the first character of the
second thru last records. On output, define a LOGICAL variable as
the line feed character and write in an A1 format, as below:
     LOGICAL LF
     LF=10
     DO 10 I=1,10
     WRITE(6, 20) I,LF 10   CONTINUE 20   FORMAT(I4,A1)
  This will write a line feed character at the end of each line
of output.  Notice that we do not need to allow one character at
the beginning of the record for carriage control, as we would if
we were writing to a printer.   Unformatted I/O is performed in
the same manner as formatted I/O, but without the FORMAT
statement.  This allows us to write records to disk files in
"memory image" or binary format, which saves disk space, and is
faster.  Files written in this manner may be read only by another
FORTRAN program, also using unformatted I/O.
  As mentioned earlier, we can use the END= and ERR= branches
with disk I/O statements.  The format of these statements is as
shown in your FORTRAN manual.  The END= will transfer control to
the specified statement number when an end of file is
encountered.  The ERR= will transfer control to the specified
statement when a physical I/O error occurs.  Note that ERR= will
NOT trap "logical" errors, such as errors in format width or
specification.   FORTRAN allows us to use a file name other than
the standard "FORTnn.DAT";  by using the OPEN subroutine.  This
statement is formatted as follows:
 CALL OPEN(filenumber,filename,  drivenumber)
  Where filenumber is the LUN (6-10) of the file, filename is the
name of the file (in quotes), and drivenumber is the drive number
according to the following table:
   drivenumber    drive
   -----------    -----
          0       currently
                  logged
          1         A:
          2         B:
             etc.
  An example of this statement is shown below.  Note that the
filename is filled to 8 spaces, and the extension to 3 spaces.
Also, the period separating the filename and the extension is
also left out.
    CALL OPEN(6,'TEST    DAT',0)
  This statement will open the file TEST.DAT on the default
drive, for use as logical unit (LUN) 6.

  COBOL
  COBOL has two different formats for sequential files.
  The first (and default) is SEQUENTIAL.  In the SEQUENTIAL
format, records are considered variable length, and each record
begins with several characters of control information.  Files
written with the SEQUENTIAL organization can be read only by
another COBOL program.
  The second format is called LINE SEQUENTIAL, and is the
familiar CP/M "text" file format.  Each record is variable
length, terminated by a carriage return/ line feed pair, and
consists of a string of ASCII characters.
  Like BASIC, COBOL sequential files may be opened for input or
output.  There is also a special mode allowed for COBOL files,
called EXTEND.  A file that is OPENed EXTEND may have records
added to it at the end of the file.
  While COBOL code is a bit to lengthy for an example here, watch
the public access space for examples of COBOL file and screen
handling in the near future.

  That's all for this issue.  In the next issue we'll talk about
random access files and how they are implemented in the various
Microsoft languages.