R help - Jul 2001 - How to write the bytes 00 01 00 to a file/connection?

Is there any way to write (8-bit) bytes to a file which works on all [R]
platforms? I have been looking at

  1) writeBin
  2) writeChar
  3) cat

and neither of them manage to write arbitrary sequences of bytes (0-255).

For instance, I would like to create a binary file of length three
containing the bytes 0, 1 and 0. I [R] I have the following vector of bytes:

  bfr <- c(0,1,0)

1) For having 'writeBin' to write bytes to a file the argument
'size' should
be one. However, this is not supported by my Windows Me system. I haven't
been able to try this on other platforms. Using 'writeBin(bfr, con)'
with
default 'size' argument will generate a file containing 00 00 00 01 00
00,
i.e. two bytes for every integer. One approach would be to convert 8-bit
bytes into 16-bit integers and then write the integers. However, this would
only work for file sizes of even length!

Another approach is to convert the bytes to a vector of characters
"\000"-"\377", which in this case would be
c("\000", "\001", "\000"). This
is possible and not too hard.

2) Using 'cat' to write strings will NOT work since it won't write
"\000"'s.
Somewhere down the stream, the "\000"'s are cut of since they are
interpret
as End of String. All other ASCII characters seems to work (I haven't tried
this fully on all systems though).

3) The third approach I tried was to use 'writeChar', which also
can't write
"\000", except by using the 'eos' argument as
eos="\000". This approach is
very awkward and requires a lot of ad-hoc coding and I am not sure it is
working the same on all platforms. Here is how you can write 00 01 00 to a
file:

  fh <- file("writeChar.bin", "w")
  writeChar("", con=fh, nchars=0, eos="\000")
  writeChar("\001", con=fh, nchars=1, eos=NULL)
  writeChar("", con=fh, nchars=0, eos="\000")
  close(fh)

If someone knows a better way of writing arbitrary byte sequences to a file,
please help me out.

Thanks

Henrik Bengtsson
h b @ m a t h s . l t h . s e

-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-
r-help mailing list -- Read http://www.ci.tuwien.ac.at/~hornik/R/R-FAQ.html
Send "info", "help", or "[un]subscribe"
(in the "body", not the subject !)  To: r-help-request at
stat.math.ethz.ch
_._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._

On Mon, 16 Jul 2001, Henrik Bengtsson wrote:
> Is there any way to write (8-bit) bytes to a file which works on all [R]
> platforms? I have been looking at
>
>   1) writeBin
>   2) writeChar
>   3) cat
>
> and neither of them manage to write arbitrary sequences of bytes (0-255).
>
You could also use

library(Rstreams)
s <- openstream("foo", "write")
writeint(s, bfr, 1)
closestream(s)

> For instance, I would like to create a binary file of length three
> containing the bytes 0, 1 and 0. I [R] I have the following vector of
bytes:
>
>   bfr <- c(0,1,0)
Nope, that's a sequence of doubles and that seems to be the problem.
> 1) For having 'writeBin' to write bytes to a file the argument
'size' should
> be one. However, this is not supported by my Windows Me system. I
haven't
> been able to try this on other platforms. Using 'writeBin(bfr,
con)' with
> default 'size' argument will generate a file containing 00 00 00 01
00 00,
> i.e. two bytes for every integer. One approach would be to convert 8-bit
> bytes into 16-bit integers and then write the integers. However, this would
> only work for file sizes of even length!
You need them to be *integers*

bfr <- as.integer(c(0,1,0))
out <- file("foo", "wb")
writeBin(bfr, out, size=1)
close(out)

works for me (including on Win2K: I have never had to use Windows Me).
That's the intended approach.

[...]

-- 
Brian D. Ripley,                  ripley at stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
1 South Parks Road,                     +44 1865 272860 (secr)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595

-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-
r-help mailing list -- Read http://www.ci.tuwien.ac.at/~hornik/R/R-FAQ.html
Send "info", "help", or "[un]subscribe"
(in the "body", not the subject !)  To: r-help-request at
stat.math.ethz.ch
_._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._