Question

在How to pass subroutine names as arguments in Fortran classes?中，我们学习了如何将子例程名称作为参数INSIDE Fortran类传递。但是我们如何从OUTSIDE类中传递子程序名？

随后的代码使用GNU Fortran（GCC）5.1.0为两次不同的尝试产生编译错误：

gfortran  -Wall -Wextra -Wconversion -Og -pedantic -fcheck=bounds -fmax-errors=5 casey.f08 
casey.f08:42:37:

         call selector ( ints % square, x , y )
                                     1
Error: Expected argument list at (1)
casey.f08:43:24:

         call selector ( ints % double ( x, y ), x , y )
                        1
Error: ‘double’ at (1) should be a FUNCTION

目标是使例程selector采用不同的计算路径：一个对数字进行平方，另一个对其进行加倍。第一个编译错误建议添加参数列表。对此的天真补救措施会产生第二个错误。

MWE如下。通过排列编程产生了许多变体;希望这个版本可以轻松解决。

module myModule

    implicit none

    type     :: intermediates
        real :: z
    contains
        private
        procedure, nopass, public :: square => square_sub
        procedure, nopass, public :: double => double_sub
    end type intermediates

    private :: square_sub
    private :: double_sub

contains

    subroutine square_sub ( x, y )
        real, intent ( in )  :: x
        real, intent ( out ) :: y
            y = x ** 2
    end subroutine square_sub

    subroutine double_sub ( x, y )
        real, intent ( in )  :: x
        real, intent ( out ) :: y
            y = x * 2
    end subroutine double_sub

end module myModule


program casey

    use myModule
    implicit none

    real :: x = 10.0, y
    type ( intermediates ) :: ints
        call selector ( ints % square, x , y )
        call selector ( ints % double ( x, y ), x , y )

contains

    subroutine selector ( sub, x, y )

        interface mySub
            subroutine sub ( x, y )
                real, intent ( in )  :: x
                real, intent ( out ) :: y
            end subroutine sub
        end interface mySub

        real, intent ( in )  :: x
        real, intent ( out ) :: y

            call sub ( x, y )
            print *, 'x = ', x, ', y = ', y

    end subroutine selector

end program casey

Answer 1

解决方案是将选择器过程放在类中。在上面的示例中，subroutine selector位于program内。 subroutine local_selector下面的procedure是mySubs类型中的module mySubs implicit none type :: myClass contains procedure, nopass, public :: square procedure, nopass, public :: double procedure, nopass, public :: local_selector end type myClass contains subroutine square ( x, y ) real, intent ( in ) :: x real, intent ( out ) :: y y = x ** 2 print *, 'x = ', x, '; x ** 2 = ', y end subroutine square subroutine double ( x, y ) real, intent ( in ) :: x real, intent ( out ) :: y y = x * 2 print *, 'x = ', x, '; 2 x = ', y end subroutine double subroutine local_selector ( sub, x, y ) interface mySub subroutine sub ( x, y ) real, intent ( in ) :: x real, intent ( out ) :: y end subroutine sub end interface mySub real, intent ( in ) :: x real, intent ( out ) :: y call sub ( x, y ) end subroutine local_selector end module mySubs program fixed use mySubs implicit none real :: x = 10.0, y type ( myClass ) :: thisClass call thisClass % local_selector ( square, x , y ) call thisClass % local_selector ( double, x , y ) end program fixed。

select column1, max(column2), min(column3)
from myTable
group by column1
order by column1

从Fortran中的外部类传递子例程名称

1 个答案: