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readBin or writeBin adds extra nulls (PR#2333)

2 messages · ken_yap_aus@yahoo.com, Brian Ripley

Original
ken_yap_aus@yahoo.com
# 
Full_Name: Ken Yap
Version: 1.6.1
OS: Linux (SuSE 8.0)
Submission from: (NULL) (129.78.64.5)


I'm trying to copy a file using readBin and writeBin. (The reason is to be able
to pipe PostScript or PDF output to a socket later, this is just an experiment.)
I do:

zz <- file("foo.ps", "rb")
r <- readBin(zz, character(), 1000000)
yy <- file("bar.ps", "wb")
writeBin(r, yy, character(), 1000000)
close(yy)
close(zz)

When I diff the files I see differences. Every 10000 characters, the output file
has
an extra null byte, and the last portion is missing. Maybe the missing part is
because I forgot to flush the output of something, if someone could explain how
to do it correctly that would be nice. The extra null byte seems to be due to an
off-by-one programming error somewhere perhaps? Or am I doing something wrong?

Thanks for the great software by the way.
Brian Ripley
# 
Please read the help page:

     `readBin' and `writeBin' read and write C-style zero-terminated
     character strings.  `readChar' and `writeChar' allow more
     flexibility, and can also be used on text-mode connections.

You don't have such character strings in a postscript file (if that is
what foo.ps is).  The code arbitrarily breaks the input into strings of
length 10000 if it gets in trouble finding a null terminator.  The bug is
not issuing a warning to the user if that happens.

You don't get the last part because there was no final null terminator,
so no qualifying string gets read.

You should be using either readChar (as the help page says) if you have a
text file, or integer() of size 1 if you really want to read a file of
bytes.
On Fri, 29 Nov 2002 ken_yap_aus@yahoo.com wrote: