FIX: Huge Number in a FORMAT Statement Halts Machine

MS-DOS               | OS/2      | WINDOWS NT

The information in this article applies to:

• Microsoft FORTRAN for MS-DOS, versions 5.0 and 5.1
• Microsoft FORTRAN for OS/2, versions 5.0 and 5.1
• Microsoft FORTRAN PowerStation for MS-DOS, versions 1.0 and 1.0a
• Microsoft FORTRAN PowerStation 32 for Windows NT, version 1.0

SYMPTOMS

Using the Microsoft FORTRAN compiler to compile a program that contains a syntax error in a FORMAT statement can cause the compiler to halt the machine under MS-DOS or to generate a protection violation under OS/2.

With FORTRAN PowerStation, the possible symptoms include:

• System Hang
• error F2001: INTEGER value overflow
• error F2115: syntax error
• error F2837: label : undefined
• warning F4989: unexpected character in format

CAUSE

The specific syntax error is caused by a comma at the beginning of a FORMAT statement, followed by a character string constant that contains large integer numbers. The real problem is having a huge number in a FORMAT statement. The out-of-place comma causes the compiler to parse the format as if the first single quotation mark isn't there. Normally, the compiler will determine at the end of the parse that the comma shouldn't be there, and the compiler will issue an error. In this case, however, the machine halts before the error output. Blanks in numbers are ignored. Having a huge number in the format causes the same problem (sample code 2). Because extremely large numbers do not make sense in FORMAT statements, the expected source of the error is the comma, which causes the string to be parsed as a number.

RESOLUTION

Correcting the syntax error eliminates the problem.

STATUS

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

MORE INFORMATION

The following code can be used to reproduce the problem.

Sample Code 1

      open(1,file='data')
      write(1,10)

      end

Sample Code 2

10 format(100000000000000000) ! Causes machine halt

      end

Sample Code 3

      open(1,file='data')
      write(1,10)
 10   format('110000 115000 120000')  ! Correct syntax
      end