我有一个未格式化的Fortran文件,其中包含不同长度的字符串,但是我无法使用Fortran本身读取这些字符串。
示例程序:
program test
implicit none
character(len=200) :: line
open(32,file="testfile",form="unformatted",action="write")
write(32) "A test string"
write(32) "Another longer test string"
close(32)
open(33,file="testfile",form="unformatted",action="read")
read(33) line
write(6,*) trim(line)
read(33) line
write(6,*) trim(line)
close(33)
end program test
此操作失败(使用gfortran编译):
At line 11 of file test.f90 (unit = 33, file = 'testfile')
Fortran runtime error: I/O past end of record on unformatted file
我可以尝试通过减小长度和后退间距(read_string
子例程)进行读取来使其正常工作,但这看起来效率很低:
program test
implicit none
character(len=200) :: line
open(32,file="testfile",form="unformatted",action="write")
write(32) "A test string"
write(32) "Another longer test string"
close(32)
open(33,file="testfile",form="unformatted",action="read")
call read_string(33,line)
write(6,*) trim(line)
call read_string(33,line)
write(6,*) trim(line)
close(33)
contains
subroutine read_string(u,string)
integer, intent(in) :: u
character(len=*), intent(out) :: string
integer :: i, error
do i=len(string),0,-1
read(u,iostat=error) string(:i)
if (error == 0) then
string(i+1:) = ''
exit
end if
backspace(u)
end do
end subroutine read_string
end program test
是否有更好的方法从未格式化的文件中读取可变长度的字符串?
我稍微修改了您的示例程序,在binary中读取了文件。这适用于英特尔的编译器; gfortran不知道二进制格式,所以是ymmv。在Intel's reference on record types上查看我的想法
program test implicit none character(len=200) :: line integer(4) recl_at_start, recl_at_end open(32,file="testfile",form="unformatted",action="write") write(32) "A test string" write(32) "Another longer test string" close(32) ! initialization is required to fill the line with blanks ! because trim() does not work on line filled with zero characters line = "" open(33,file="testfile",form="binary",action="read") read(33) recl_at_start read(33) line(1:recl_at_start) read(33) recl_at_end write(6,*) trim(line) read(33) recl_at_start read(33) line(1:recl_at_start) read(33) recl_at_end write(6,*) trim(line) close(33) end program test
其输出为
不再需要了。只需使用测试字符串另一个更长的测试字符串
现在您知道行长,trim()
write(6,*) line(1:recl_at_start)
这还可以防止在将“较短的测试字符串”添加到数据时出现麻烦。