Temporary Files And Directories in Fortran

Our program will demonstrate how to work with temporary files and directories in Fortran. Here’s the full source code:

program temp_files_and_dirs
    use, intrinsic :: iso_fortran_env, only: error_unit
    use, intrinsic :: iso_c_binding, only: c_char, c_null_char
    implicit none

    character(len=:), allocatable :: temp_file_name, temp_dir_name
    integer :: unit_num, iostat
    character(len=100) :: error_msg

    ! Create a temporary file
    call create_temp_file(temp_file_name)
    print *, "Temp file name:", temp_file_name

    ! Write some data to the file
    open(newunit=unit_num, file=temp_file_name, status='replace', action='write', iostat=iostat, iomsg=error_msg)
    if (iostat /= 0) then
        write(error_unit,*) "Error opening file: ", trim(error_msg)
        stop
    end if
    write(unit_num, '(4I1)') 1, 2, 3, 4
    close(unit_num)

    ! Create a temporary directory
    call create_temp_dir(temp_dir_name)
    print *, "Temp dir name:", temp_dir_name

    ! Create a file in the temporary directory
    call create_file_in_dir(temp_dir_name)

    ! Clean up
    call delete_file(temp_file_name)
    call delete_directory(temp_dir_name)

contains

    subroutine create_temp_file(file_name)
        character(len=:), allocatable, intent(out) :: file_name
        character(len=15) :: template = "sampletempXXXXXX"
        integer :: fd

        allocate(character(len=256) :: file_name)
        call mkstemp(template, fd, file_name)
        close(fd)
    end subroutine create_temp_file

    subroutine create_temp_dir(dir_name)
        character(len=:), allocatable, intent(out) :: dir_name
        character(len=19) :: template = "sampledirtempXXXXXX"

        allocate(character(len=256) :: dir_name)
        call mkdtemp(template, dir_name)
    end subroutine create_temp_dir

    subroutine create_file_in_dir(dir_name)
        character(len=*), intent(in) :: dir_name
        character(len=:), allocatable :: full_path
        integer :: unit_num, iostat
        character(len=100) :: error_msg

        full_path = trim(dir_name) // "/file1"
        open(newunit=unit_num, file=full_path, status='replace', action='write', iostat=iostat, iomsg=error_msg)
        if (iostat /= 0) then
            write(error_unit,*) "Error creating file in directory: ", trim(error_msg)
            return
        end if
        write(unit_num, '(2I1)') 1, 2
        close(unit_num)
    end subroutine create_file_in_dir

    subroutine delete_file(file_name)
        character(len=*), intent(in) :: file_name
        logical :: exist
        integer :: iostat

        inquire(file=file_name, exist=exist)
        if (exist) then
            open(unit=10, file=file_name, status='old', iostat=iostat)
            if (iostat == 0) close(10, status='delete')
        end if
    end subroutine delete_file

    subroutine delete_directory(dir_name)
        character(len=*), intent(in) :: dir_name
        character(len=1024) :: command

        write(command, '(3A)') 'rm -rf "', trim(dir_name), '"'
        call execute_command_line(command)
    end subroutine delete_directory

end program temp_files_and_dirs

This Fortran program demonstrates how to work with temporary files and directories. Here’s a breakdown of what it does:

We create a temporary file using the create_temp_file subroutine, which uses the mkstemp function to generate a unique filename.
We write some data to the temporary file.
We create a temporary directory using the create_temp_dir subroutine, which uses the mkdtemp function to generate a unique directory name.
We create a file inside the temporary directory.
Finally, we clean up by deleting both the temporary file and directory.

Note that Fortran doesn’t have built-in functions for creating temporary files and directories like some other languages do. We’ve used the POSIX functions mkstemp and mkdtemp, which may not be available on all systems. For a more portable solution, you might need to implement your own temporary file/directory creation logic.

To compile and run the program:

$ gfortran -o temp_files_and_dirs temp_files_and_dirs.f90
$ ./temp_files_and_dirs
Temp file name: /tmp/sampletemp123456
Temp dir name: /tmp/sampledirtemp789012

The exact output will vary as the filenames and directory names are generated randomly to ensure uniqueness.

Remember to handle errors appropriately in a production environment, and be aware of the security implications of creating and deleting files and directories.

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Temporary Files And Directories in Fortran