R: load warnings - r

Question

I have a file foo, which based on file utility is:
foo: LaTeX 2e document, UTF-8 Unicode text, with CRLF, LF line terminators
I have the following meta-code
txt <- readLines("foo")
....
save(txt, file="bar")
load("bar")
There were 50 or more warnings (use warnings() to see the first 50)
warnings()
Warning messages:
1: In load("bar") :
input string '...' cannot be translated to UTF-8, is it valid in 'ANSI_X3.4-1968'?
2: ...
The warnings cause some parts of the txt character vector to be cut when I later save it with writeLines
I was unable to find an explanations for the warnings. The warnings occur for lines in the TeX file with accented letters

Answer 1

In Linux, R reacts to the value of the LANG environment variable. If it is not set to an UTF-8 locale, R is unable to manage this type of encoding.
So if, calling R like so (no UTF-8):
LANG=en_US R
the console gives:
a <- rawToChar(as.raw(c(0xc3, 0xa0)))
a
# [1] "\303\240"
tmp <- file("/tmp/foo", encoding="UTF-8")
writeLines(a, tmp)
# Warning message:
# In writeLines(a, tmp) : invalid char string in output conversion
close(tmp)
readLines("/tmp/foo")
# character(0)
Without an UTF-8 locale, the value of a (an accented a) is printed as raw bytes.
Forcing UTF-8 encoding when writing to a file gives a warning and nothing is printed.
Calling with:
LANG=en_US.UTF-8 R
does not give errors:
a <- rawToChar(as.raw(c(0xc3, 0xa0)))
a
# [1] "à"
tmp <- file("/tmp/foo", encoding="UTF-8")
writeLines(a, tmp)
close(tmp)
readLines("/tmp/foo")
# [1] "à"
The problem here is that it is difficult to create portable scripts, because their results depends on the environment variables.
In Windows, R does not react to the LANG variable and the encoding depends on the language of Windows installed. For Latin languages this is ANSI. That makes simple the portability inside Windows, but R does not read properly Linux data files, based on UTF-8.