FIX: "Integer divide by 0" Error Handling

MS-DOS      | WINDOWS NT

The information in this article applies to:

• Microsoft FORTRAN PowerStation for MS-DOS, versions 1.0 and 1.0a
• Microsoft FORTRAN PowerStation 32 for Windows NT, version 1.0

SYMPTOMS

In code, there are two significant problems with dividing by 0:

• "Integer divide by 0" is not generated as a run-time error. Instead, one of two error messages is produced:

      - Under MS-DOS, the DOSXMSF error message is produced:
  

           DX1020 unhandled exception: divide by zero exception
  
      - Under Windows NT, the Dr. Watson error message is produced:
  
           exception: divide by zero
  
  

• With optimization on, the compiler replaces any constant expression that contains an "Integer divide by 0" with 0, which is incorrect, and produces the following error message:

        warning F4723: potential divide by 0
  

  (With optimization on, but warnings off, the compiler fails to generate an error or warning, either during compilation or run time.)

STATUS

Microsoft has confirmed this to be a bug in the Microsoft products listed at the beginning of this article. This problem was corrected in Microsoft FORTRAN PowerStation 32, version 4.0.

MORE INFORMATION

To generate the "Integer divide by 0" exceptions, compile and run the "Sample Code 1," below. With optimization off, the exception occurs on the first print statement. With optimization on, it occurs on the second print statement.

NOTE: FORTRAN PowerStation for MS-DOS, version 1.0, correctly generates error F6003 in this case.

To produce the invalid code generation and warning F4723, compile and run either sample with optimization on (option /Ox). To demonstrate invalid code generation with no warnings or errors, compile and run "Sample Code 2," below, with optimization on and warnings off (/Ox /W0). With optimization off (default option), "Sample Code 2" will correctly generate the run-time error for "Integer divide by 0": M6103.

NOTE: /4Yb ($DEBUG) does not produce any additional error messages.

Sample Code 1

c compile options needed: See text above.

      integer i,j
      character*4 c /"0"/
      i=0
      j=1
      print *, ' 1/0 =',j/i
      read(c,'(I1)') i
      print *, ' 1/0 =',j/i
      end

Sample Code 2

c compile options needed: See text above.

      real a,b
      a=0
      b=1
      print *, ' 1.0/0.0 =',b/a
      end