[R] End of File for binary files

[Henrik Bengtsson]

On Sun, Jan 24, 2010 at 3:56 AM, Duncan Murdoch <murdoch at stats.uwo.ca> wrote:
> On 23/01/2010 10:40 PM, rn00b wrote:
>>
>> I am using readBin to continuously read characters from the binary file.
>> I'm
>> trying to figure out how many characters are in the file. What I would
>> like
>> to do is something like
>> (while! EOF)
>> {
>> charRead <-.Internal(readBin(con,"character",1L,NA,TRUE,swap))
>> i++
>> }
>>
>> I'm not clear on how to determine the EOF condition in this case.
>
> You should not be calling .Internal.  It's for internal use, subject to
> change, etc.
>
> Using readBin(...)  you can detect EOF by reading fewer than n items when
> you ask for n.

Is this safe?  Is EOF the only case where readBin() returns fewer
elements than you requested?  Does it depend on the type of connection
you are reading from?  Does it depend on OS?

The help("readBin") does not say much about this, but it says:

"If readBin(what = character()) is used incorrectly on a file which
does not contain C-style character strings, warnings (usually many)
are given. From a file or connection, the input will be broken into
pieces of length 10000 with any final part being discarded."

which seems to suggest that you (at least in special cases) can get
fewer items than requested without hitting EOF.  EOF behavior might be
document elsewhere in R.

/Henrik

> So the loop would be something like
>
> while (length(charRead <- readBin(con, "character")) > 0) {
>  i <- i + 1
> }
>
> Duncan Murdoch
>
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