Q98757: FIX: Binary (or Unformatted) I/O Fails, Array Size > 64K

Article: Q98757
Product(s): Microsoft Fortran Compiler
Version(s): 1.0
Operating System(s): 
Keyword(s): 
Last Modified: 24-MAR-2000

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The information in this article applies to:

- Microsoft FORTRAN PowerStation for MS-DOS, version 1.0 
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SYMPTOMS
========

An application developed in Microsoft FORTRAN PowerStation that reads or writes
an array larger than 64K in size to a binary or unformatted file may read or
write an incorrect quantity of data.

CAUSE
=====

The application specifies the name of an array without a subscript or specifies
a simple variable for the subscript. The compiler does not generate the correct
code to access the low-level functions that perform binary or unformatted I/O.
Consequently, the application reads or writes the amount of data specified by
the following formula: (size of array) modulus 64K.

RESOLUTION
==========

To work around this problem, use an explicit implied DO loop in the I/O
statement. If the array has only one dimension, the array subscript must be an
expression and not a simple variable for the compiler to generate the correct
code. If the array is a multi-dimensional array, then the normal,
multi-dimensional implied DO loop is sufficient to avoid the problem.

STATUS
======

Microsoft has confirmed this to be a problem in Microsoft PowerStation version
1.0. This problem has been resolved with FORTRAN PowerStation maintenance
release version 1.0a for MS-DOS.

FORTRAN PowerStation version 1.0 can be differentiated from the maintenance
release version 1.0a by invoking the linker. Typing "link32 | more" from
\F32\BIN directory will show version 2.8 for FORTRAN PowerStation version 1.0,
and it will show version 1.0f for the maintenance release version 1.0a.

MORE INFORMATION
================

Sample Code #1
--------------

  C Compile options needed: none
  C This program generates the following output
  C
  C     Program failed, number of bytes read:           1

        parameter(n = 64 * 1024 + 1)  ! 64K + 1 size
        character*1 arr(n), chr
        integer*4 i

        open(1, file = 'test.dat', form = 'binary')
        arr = 'x'      ! initialize entire array to 'x'
        write(1) arr   ! write entire array
        rewind(1)      ! rewind to read file
        do i = 1, n
          read(1, iostat = ierr) chr ! read a byte at a time
          if (ierr .eq. -1) exit     ! exit at end of file
        end do
        if (i - 1 .ne. n) then
          print *, 'Program failed, number of bytes read: ', i - 1
        else
          print *, 'Program OK, number of bytes read: ', i - 1
        end if
        end

Sample Code #2
--------------

  C Compile options needed: none
  C This program generates the following output
  C
  C     Program OK, number of bytes read:       65537

        parameter(n = 64 * 1024 + 1)  ! 64K + 1 size
        character*1 arr(n), chr
        integer*4 i

        open(1, file = 'test.dat', form = 'binary')
        arr = 'x'      ! initialize entire array to 'x'
        write(1) (arr(i + 0), i = 1, n)   ! note the addition of zero
        rewind(1)      ! rewind to read file
        do i = 1, n
          read(1, iostat = ierr) chr ! read a byte at a time
          if (ierr .eq. -1) exit     ! exit at end of file
        end do
        if (i - 1 .ne. n) then
          print *, 'Program failed, number of bytes read: ', i - 1
        else
          print *, 'Program OK, number of bytes read: ', i - 1
        end if
        end

Additional query words: 1.00 buglist1.00 fixlist1.00a

======================================================================
Keywords          :  
Technology        : kbAudDeveloper kbFortranSearch kbZNotKeyword3 kbFORTRANPower100DOS
Version           : :1.0
Issue type        : kbbug
Solution Type     : kbfix

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