如何停止子程序并升起标志？

I am writing a program in Fortran 95 (to be compiled with with gfortran) containing a subroutine that performs a certain computation. As suggested in "Fortran 95/2003 for Scientists & Engineers" by S. J. Chapman, I am trying to stop the subroutine when an error is encountered and "throw"^[1] an error flag that is "catch"ed^[1] by the calling program, that will take all the necessary actions. Ideally, I am going for something like:

! Pseudo-code
PROGRAM my_prog
    integer :: error_flag
    CALL my_subr (<input_args>, <output_args>, error_flag)
    ! Also error_flag is an output: 0 -> everything OK, 1 -> error
    IF (error_flag /= 0) THEN
        WRITE (*,*) 'Error during execution of "my_subr"'
    ELSE
        ... do something ...
    END IF
END PROGRAM my_prog

如何停止子例程并优雅地处理错误？

这是一个例子：subroutine“division”采用整数输入值，并迭代地将其除以输入值减去步骤数-1 的值。当该值达到零时，应提出标志并退出子例程而不执行除以零。

SUBROUTINE division (inval, outval, error_flag)
  IMPLICIT NONE

  INTEGER, INTENT(IN) :: inval
  REAL, INTENT(OUT) :: outval
  INTEGER, INTENT(OUT) :: error_flag ! 0 -> OK, 1 -> error

  INTEGER :: i
  REAL :: x

  error_flag = 0
  x = REAL(inval)
  DO i = 0, 10
     IF (inval-i == 0) error_flag = 1
     ! How can I gracefully exit now?
     x = x / REAL(inval-i)
  END DO

END SUBROUTINE division

PROGRAM my_prog
  IMPLICIT NONE
  REAL :: outval
  INTEGER :: error_flag
  CALL division (8, outval, error_flag)
  IF (error_flag == 1) THEN
     WRITE (*,*) 'Division by zero'
  ELSE
     WRITE (*,*) 'Output value:', outval
  END IF
END PROGRAM my_prog

Notes:

^[1] I am borrowing (in a probably inappropriate way) C++'s jargon.

看到你的例子，你似乎错过了return陈述：

  error_flag = 0
  x = REAL(inval)
  DO i = 0, 10
     IF (inval-i == 0) then
                         error_flag = 1
                         return
     END IF

     x = x / REAL(inval-i)
  END DO