[ncl-talk] Writing binary characters while invoking WriteByteOrder

[Kay Shelton]

Hello ncl-talkers,

I have a little bit of a conundrum with trying to write a binary file for a
colleague that is destined to be used in TELEMAC-2D. The binary file that I
am trying to write needs to include characters, integers and floats, and
will be used on a machine that is Big Endian. I am creating the file on a
Linux machine that is Little Endian, hence when I write the binary file I
am using "setfileoption("bin","WriteByteOrder","BigEndian")". This all
works fine for integers and floats, but the characters are not correctly
represented in the output binary.

I have written a short piece of code that demonstrates the problem
succinctly:

--------------------------------------------------------
begin

endianness = isbigendian()
words = "blah_de_blah_de_blah"
words_char = new(strlen(words),character)
words_char = tochar(" ")
words_char(0:strlen(words)-1) = tochar(words)
outfil = "temp.bin"

if (.not.endianness) then
  print("Endianness is LittleEndian")

; run and look at results, then uncomment the next two lines and re-run
;  setfileoption("bin","ReadByteOrder","BigEndian")
;  setfileoption("bin","WriteByteOrder","BigEndian")

  if (fileexists(outfil)) then
    system("rm -f "+outfil)
  end if
  fbinrecwrite (outfil,0, (/ words_char /))
  new_words = fbinrecread(outfil, 0, -1, "character")
  print("WORDS (original): $$ "+words+" $$")
  print("WORDS (original, char to str): $$ "+tostring(words_char)+" $$")
  print("NEW_WORDS (char to str): $$ "+tostring(new_words)+" $$")
else
  print("Already BigEndian")
end if

end
--------------------------------------------------------

I have tested this on two completely different Linux machines running NCL
6.3.0 (both 64-bit Ubuntu) and also on one of them using NCL 6.2.1. All
give the same result.

Running the script first time with the two setfileoption lines commented
out (i.e. native LittleEndian binary):
(0)     Endianness is LittleEndian
(0)     WORDS (original): $$ blah_de_blah_de_blah $$
(0)     WORDS (original, char to str): $$ blah_de_blah_de_blah $$
(0)     NEW_WORDS (char to str): $$ blah_de_blah_de_blah $$

Running with the two setfileoption lines un-commented:
(0)     Endianness is LittleEndian
(0)     WORDS (original): $$ blah_de_blah_de_blah $$
(0)     WORDS (original, char to str): $$ blah_de_blah_de_blah $$
(0)     NEW_WORDS (char to str): $$  $$

As you can see with the BigEndian option the characters are not correctly
written to the file.

Is this correct behaviour? Have I missed something I should have included
to get this to work? (This is entirely possible and I apologise for wasting
your time if this is a simple user-error.)

I have searched the ncl-talk archives and have not found this problem
encountered by others, so it may well be an issue exclusive to my machines.
If it is, I can work around it by wrapping in some fortran to handle the
reading and writing of the binary correctly. I would prefer to avoid such a
work around as the size of the arrays in the binary files I have to read
and write will vary, and I would prefer not to have to hard-code the array
sizes when NCL makes calls to the fortran code.

[Note: on the machine running NCL 6.2.1 I also get the following warning
message on both attempts:
warning:fbinrecwrite: end of file reached before record number, writing
record as last record in file]

Many thanks for your help,
Kay
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