Modules at Scale

Private by Default

Public Surface

A larger module is easier to maintain when names are private by default and only the intended API is public.

Program

Play the program to choose a count and call the one public formatting function.

private_public.f90 
module catalog_mod
    implicit none
    private
    public :: label_count
contains
    function label_count(count) result(label)
        integer, intent(in) :: count
        character(len=16) :: label
        write(label, '(A,I0)') 'items=', count
    end function label_count
end module catalog_mod

program private_public_demo
    use catalog_mod, only: label_count
    implicit none
    integer :: count
    character(len=16) :: label

    count = 
    label = label_count(count)
    print '(A)', trim(label)
end program private_public_demo

module catalog_mod
    implicit none
    private
    public :: label_count
contains
    function label_count(count) result(label)
        integer, intent(in) :: count
        character(len=16) :: label
        write(label, '(A,I0)') 'items=', count
    end function label_count
end module catalog_mod

program private_public_demo
    use catalog_mod, only: label_count
    implicit none
    integer :: count
    character(len=16) :: label

    count = 
    label = label_count(count)
    print '(A)', trim(label)
end program private_public_demo

module catalog_mod
    implicit none
    private
    public :: label_count
contains
    function label_count(count) result(label)
        integer, intent(in) :: count
        character(len=16) :: label
        write(label, '(A,I0)') 'items=', count
    end function label_count
end module catalog_mod

program private_public_demo
    use catalog_mod, only: label_count
    implicit none
    integer :: count
    character(len=16) :: label

    count = 
    label = label_count(count)
    print '(A)', trim(label)
end program private_public_demo
private `private` hides module names unless they are explicitly exported.
public API `public :: label_count` keeps one supported entry point visible.
character result A function can return a fixed-length character value and callers can `trim` it.