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Manual Reference Pages  - next (3fortran)

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NAME

NEXT(3) - [ENUMERATION] Next enumeration value

SYNOPSIS

result = next (a [, stat])

         elemental enumerator function next(a,stat) result(answer)

          enumerator,intent(in) :: a
          integer(kind=**),intent(out),optional :: stat
          enumerator :: answer

CHARACTERISTICS

o	A shall be of enumeration type.
o	STAT is an integer with a decimal exponent range of at least four.
o	The returned value will be of the same type and kind as the argument.

DESCRIPTION

Next enumeration value

OPTIONS

o	A : The starting value to use to locate the next value from
o	STAT : If A is equal to the last enumerator of its type, it is assigned a processor-dependent positive value; otherwise, it is assigned the value zero. If STAT would have been assigned a nonzero value but is not present, error termination is initiated.

RESULT

If A is equal to the last enumerator of its type, the value of the result is that of A. Otherwise, the value of the result is the next enumerator following the value of A.

For example, if the enumerators of an enumeration type are EN1, EN2, EN3, and EN4, NEXT (EN1) is equal to EN2, and NEXT (EN4, ISTAT) is equal to EN4 and a positive value is assigned to ISTAT.

Sample program:

    !program demo_next
    module enumeration_mod

    enumeration type :: v_value
       enumerator :: v_one, v_two, v_three
       enumerator v_four
    end enumeration type

    enumeration type :: w_value
       enumerator :: w1, w2, w3, w4, w5, w_endsentinel
    end enumeration type

    contains

    subroutine sub(a)
    type(v_value),intent(in) :: a
       print 1,a ! Acts similarly to Print *,Int(a).
    1  format(’A has ordinal value ’,i0)
    end subroutine

    subroutine wcheck(w)
    type(w_value),intent(in) :: w
       select case(w)
        case(w1)
          print *,’w1 selected’
        case (w2:w4)
          print *,’One of w2...w4 selected’
        case (w_endsentinel)
          stop ’Invalid w selected’
        case default
          stop ’Unrecognized w selected’
       end select
    end subroutine

    end module
    program demo_next
    ! Here is an example of a program using that module.
    use enumeration_mod
    type(v_value) :: x = v_one
    type(v_value) :: y = v_value(2)  ! Explicit constructor producing v_two.
    type(v_value) :: z,nz            ! Initially undefined.
       call sub(x)
       call sub(v_three)
       z = v_value(1)                ! First value.
       do
          if (z==huge(x)) write (*,’(A)’,advance=’No’) ’ Huge:’
          call sub(z)
          nz = next(z)
          if (z==nz) exit
          z = nz
       end do

    end program demo_next

Results:

     >
     >

Here is an example showing some invalid usages of enumerations.

Program invalid Use enumeration_mod

    Type(v_value) :: a, b
       a = 1         ! INVALID - wrong type (INTEGER).
       b = w1        ! INVALID - wrong enumeration type.
       Print *,a     ! INVALID - list-directed i/o not available.
    End Program

An enumeration type can be used to declare components, for example:

    Module example2
    Use enumeration_mod
    Type vw
       Type(v_value) v
       Type(w_value) w
    End Type

    Contains
    Subroutine showme(ka)
    Type(vw),Intent(In) :: ka
       Print 1,ka
    1  Format(1X,’v ordinal is ’,I0,’, w ordinal is ’,I0)
    End Subroutine
    End Module

STANDARD

Fortran 2023

SEE ALSO

o	Next enumeration value: PREVIOUS(3)
o	Conversion of position to INTEGER: INT(3)

Fortran intrinsic descriptions

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