FUNCTION assoc_xdf,fname,lines=lines,columns=columns,datatype=datatype,typecode=typecode,header=header,nocompress=nocompress
  f = open_xdf(fname,lines=lines,columns=columns,datatype=datatype,typecode=typecode,header=header,nocompress=nocompress)

  outarr = make_array(1,type=typecode)
  point_lun,f*(-1),pos

  zinfoname='binfo'+strtrim(string(fix(randomu(seed)*10000)),2)+'.inf'
  openw,f2,zinfoname,/get_lun,/xdr
  writeu,f2,outarr
  free_lun,f2
  openr,f2,zinfoname,/get_lun,/xdr
  point_lun,f2*(-1),pos1
  readu,f2,outarr
  point_lun,f2*(-1),pos2
  arrsize = pos2-pos1
  free_lun,f2
  file_delete,zinfoname,/quiet

  ;arrsize is the size of one element

  ;need to know: one element size, one column size (element * lines)
  colsize = long(arrsize) * long(lines)

  IF NOT keyword_set(header) THEN header = 0

  return, {fptr : f, fpos : pos, fsize : arrsize, ftype : typecode, fcols : columns, flines : lines, fheader : header, fcolsize : colsize}
END