Hi all,
On Windows I'm seeing the following:
> tf <- tempfile()
> writeBin(charToRaw("\r\r\n"), tf)
> readLines(file(tf, "r"))
[1] ""
> readLines(file(tf, "rb"))
[1] "" "" ""
The former matches Guido's observation of a disappearing line (also on Windows),
the latter seems to correspond to Duncan's observation of an extra line on
MacOS.
As mentioned before, according to the docs in ?readLines it seems both should
result in c("", ""):
> Whatever mode the connection is opened in, any of LF, CRLF or CR will be
> accepted as the EOL marker for a line.
Inspecting the source [1], Rconn_fgetc endeavours to convert CR and CRLF to LF,
but on encountering the sequence \r\r returns \n and stores \n in the saved
character buffer, resulting in CR, CRLF being interpreted as LF, LF, LF.
I believe that accounts for the extra new line on MacOS (and Linux) and in
binary mode on Windows, but leaves the disappearing line in text mode on Windows
a bit of a mystery still.
Best,
Mikko
[1]:
https://github.com/wch/r-source/blob/ff4be744953e2702f4194f01f669b7c93b44933e/src/main/connections.c#L4315C1-L4323C11
-----Original Message-----
From: R-help <r-help-boun...@r-project.org> On Behalf Of Duncan Murdoch
Sent: Wednesday, 25 June 2025 15:03
To: Heuvel, E.G. van den (Guido) <g.vandenheu...@cbs.nl>;
'r-help@R-project.org' <r-help@R-project.org>
Subject: Re: [R] Potential bug in readLines when reading empty lines
On 2025-06-25 2:59 a.m., Heuvel, E.G. van den (Guido) via R-help wrote:
> Hi all,
>
> I encountered some weird behaviour with readLines() recently, and I am
> wondering if this might be a bug, or, if it is not, how to resolve it. The
> issue is as follows:
>
> If I have a text file where a line ends with just a carriage return (\r, CR)
> while the next line is empty and ends in a carriage return / linefeed (\r\n,
> CR LF), then the empty line is skipped when reading the file with readLines.
> The following code contains a test case:
>
> ---
> print(R.version)
> # platform x86_64-w64-mingw32
> # arch x86_64
> # os mingw32
> # crt ucrt
> # system x86_64, mingw32
> # status
> # major 4
> # minor 4.0
> # year 2024
> # month 04
> # day 24
> # svn rev 86474
> # language R
> # version.string R version 4.4.0 (2024-04-24 ucrt)
> # nickname Puppy Cup
>
> txt_original <- paste0("Line 1\r", "\r\n", "Line 3\r\n")
Doesn't that produce the same thing as "Line 1\r\r\nLine 3\r\n" when you write
it with writeBin? If I read the ?readLines page correctly, that string
contains 3 lines:
Line 1 CR
CR LF
Line 3 CR LF
On the other hand, when I use your construction or mine, I get 4 lines read by
my Mac:
readLines("test.txt")
[1] "Line 1" "" "" "Line 3"
I'd guess it is processing it as
Line 1 CR
CR
LF
Line 3 CR LF
So I think there are definitely bugs or bad docs here.
Duncan Murdoch
>
> # Write txt_original as binary to avoid unwanted conversion of end of
> line markers writeBin(charToRaw(txt_original), "test.txt")
>
> txt_actual <- readLines("test.txt")
> print(txt_actual)
> # [1] "Line 1" "Line 3"
> ---
>
> I included the output of this script on my machine in the comments. I would
> expect txt_actual to be equal to c("Line 1", "", "Line 3"), but the empty
> line is skipped.
>
> Is this a bug? And if not, how should I read test.txt in such a way that the
> empty 2nd line is left intact?
>
> Best regards,
>
> Guido van den Heuvel
> Statistics Netherlands
>
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