Example of Using EXTERNAL for User-Defined Function

• Microsoft FORTRAN for MS-DOS versions 4.0, 4.01, 4.1, 5.0, 5.1
• Microsoft FORTRAN for OS/2, versions 4.1, 5.0, 5.1
• Microsoft FORTRAN PowerStation for MS-DOS, versions 1.0 and 1.0a
• Microsoft FORTRAN PowerStation 32 for Windows NT, version 1.0 and 4.0

SUMMARY

In a FORTRAN application, the EXTERNAL statement specifies that a user-defined name is a subroutine or function that can be used as a formal argument. In addition, an application can use the EXTERNAL statement to replace an intrinsic function with a user-defined function of the same name.

The following code example demonstrates using the EXTERNAL command to specify a user-defined function in a FORTRAN application.

Sample Code

C Compile options needed: None

      FUNCTION FN (X)
        REAL FN, X
        FN = X
      END

      SUBROUTINE S2 (F, X, Y)
        REAL F, X, Y
        X = F(Y)
      END

      REAL Y, Z, FN
      EXTERNAL FN
      Z = 10.0
      CALL S2(FN, Y, Z)
      WRITE (*, *) Y
      END