npts = 20
x    = float(randomu(1234,npts))
y    = x[sort(x)]
z    = x^2


;+++++++++++++++++++++++++++++++++++++++++
; fortran binary files                   +
;+++++++++++++++++++++++++++++++++++++++++
; You'll need to write the files first. Download and run the fortran
; programme .....


; read the ascii file
openr,unit,'myascii.dat',/get_lun
n = 0l & j=1l
readf,unit,n
x = fltarr(n)
data = 1.0
for i=0,n_elements(x)-1 do begin $
  & readf,unit,j,data $
  & x[i]=data $
  & endfor
close,unit
free_lun,unit

; ditto for binary file
openr,unit,'mybin.dat',/get_lun,/f77_unformatted,/swap_endian
n = 0l
readu,unit,n
a= fltarr(n)
readu,unit,a
free_lun,unit

; check
for i=0,n-1 do print,' i = ',i,' ascii value = ',x[i],' binary value = ',a[i]


; things to note:

; readf,unit,j,x[i]  does not seem to work. Hence I read the value as
; "data" first, then copy it into x

; Note the /swap_endian keyword to openr. It is easy to change the
; endian-ness like this, but it does show the extreme limitation of
; unformatted (binary) files. If you run idl and f90 on the same
; computer, you should not need the /swap_endian, but I wrote them on
; my pc (because the suns do not have f95), then read them on the sun.
;