[Rd] "\0" gives no warning "unknown escape sequence" (PR#11107)

[Duncan Murdoch]

volkmar.klatt at bnv-bamberg.de wrote:
> Full_Name: Volkmar Klatt
> Version: 2.6.2
> OS: linux
> Submission from: (NULL) (84.147.0.178)
>
>
> Hello,
>
> the documentation article
> ?Quotes 
> from package:base could be improved by discussing
> the meaning of "\0" escape sequence.
>   

I agree...

> In R (currently used: R-2.6.2), a "\0" in a string will
> silently terminate that string, just as it would in C code.
> There is no warning about an unknown escape sequence.
> (cf. R FAQ 7.37)
>
> # example:
> s <- "abc\0def"
> s
> # --> [1] "abc"
> nchar(s) 
> # --> [1] 3
>
> The "\0" seems to be so fundamental, that it cannot be handled by
> any R function, am I right?
>   

Not quite.  The parser will stop parsing a string when it hits one, but 
you could embed one in a string using something like

 > rawToChar(as.raw(c(97:99, 0, 100:102)))
[1] "abc\0def"

> E.g., the function escapeBS (package:Hmisc) does not correctly
> handle "\0" sequences, that is in contrast to what is stated in its 
> article ?escapeBS :
> "'escapeBS' will escape any backslash '\backslash' in a string.
>
>   

But there was no backslash in that string, escapeBS only saw the "abc" 
part that the parser gave it.

I don't know that the parser should be able to handle input like 
"abc\0def", but it does make sense that it would, since that's a legal 
character vector.

Duncan Murdoch
> # example:
> library(Hmisc)
> escapeBS("abc\0def")
> # -->[1] "abc"
>
> Bye,
> Volkmar Klatt
> volkmar.klatt AT bnv-bamberg.de
>
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