如何在Fortran中读取可能包含很长行的文本文件

Question

例如,假设我有一个文本文件可能包含很长的文本行

short
short
reeeeeeeeeeeeeeeeeeeeeeaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaally loooooooooooooooooooooooooooooooooooooooooooooooooooooooooooonnnnggg
short as well
short

我可以编写一个读取此文件的简单程序:

program main
implicit none
integer, parameter        :: BIG_NUMBER = 400
integer                   :: lun
character(len=BIG_NUMBER) :: line
integer                   :: istat

open(newunit = lun, file = 'myfile')

do
   read (lun, '(A)', iostat = istat) line
   if (istat /= 0) exit
end do

end program main

这仅支持文本文件,其中所有行不超过400个字符.在C中,使用指针,类似的程序会自动支持任何文本文件.

如何以可以读取所有长度的行的方式重写示例程序？

Answer 1

您可以使用非前进输入将行的连续块读取到缓冲区中,然后将每个块组合在一起以形成延迟长度字符变量中的完整行.例如:

subroutine get_line(lun, line, iostat, iomsg)
  integer, intent(in)           :: lun
  character(len=:), intent(out), allocatable :: line
  integer, intent(out)          :: iostat
  character(*), intent(inout)   :: iomsg

  integer, parameter            :: buffer_len = 80
  character(len=buffer_len)     :: buffer
  integer                       :: size_read

  line = ''
  do
    read ( lun, '(A)',  &
        iostat = iostat,  &
        iomsg = iomsg,  &
        advance = 'no',  &
        size = size_read ) buffer
    if (is_iostat_eor(iostat)) then
      line = line // buffer(:size_read)
      iostat = 0
      exit
    else if (iostat == 0) then
      line = line // buffer
    else
      exit
    end if
  end do
end subroutine get_line