[Rd] writeChar

[Kasper Daniel Hansen]

I have recently been using writeChar and writeBin to write binary  
files. These functions makes it very easy to write OS-independent  
files, which I am very happy with.

I have however found a few issues, best illustrated by a short example

 > con <- file("test", open = "wb")
 > writeChar(as.character(c("ab", "ab")), nchars = c(3), con = con,  
eos = "")
Warning message:
writeChar: more characters requested than are in the string - will  
zero-pad
 > close(con)
 > system("hexdump -Cv test")
00000000  61 62 00 00                                       |ab..|
00000004

As seen from this example, the fact that nchars is shorter than the  
character vector being written results in the remaining elements  
being skipped. Also, the nchars argument is not being recycled,  
something I find quite R-counter-intuitive. I would suggest  
recycling, although I am not sure how to best achieve this.

I also get a warning about zero-padding - even if I request more  
characters than present in the vector. This means that I get a  
warning if using the argument for "what is what meant for" (at least  
in my opinion). Right now I get many warnings when writing the binary  
files I am working with, which might be confusing to future users. I  
would suggest to only give a warning if requesting _less_ characters,  
since in that case R would truncate the argument.

Finally, having a NA or a negative number (not shown) in the nchars  
argument makes R crash, at least on two platforms:

 > con <- file("test", open = "wb")
 > writeChar(as.character(c("ab", "ab")), nchars = c(3, NA), con =  
con, eos = NULL)

*** caught bus error ***
address 0x2008000, cause 'invalid alignment'

This is reproducible using R-2.3.0 (patched) on 32bit Linux:

 > con <- file("test", open = "wb")
 > writeChar(as.character(c("ab", "ab")), nchars = c(3, NA), con =  
con, eos = NULL)

*** caught segfault ***
address 0x1a5c000, cause 'memory not mapped'
Segmentation fault

I have not tested it on R-devel, but the news file does not indicate  
any changes in writeChar.

Kasper