| readChar {base} | R Documentation |
Transfer Character Strings To and From Connections
Description
Transfer character strings to and from connections, without assuming they are null-terminated on the connection.
Usage
readChar(con, nchars)
writeChar(object, con,
nchars = nchar(object, type="chars"), eos = "")
Arguments
con |
A connection object, or a character string naming a file, or a raw vector. |
nchars |
integer, giving the lengths in characters of (unterminated) character strings to be read or written. Must be >= 0 and not missing. |
object |
A character vector to be written to the connection, at
least as long as |
eos |
‘end of string’: character string . The terminator
to be written after each string, followed by an ASCII |
Details
These functions complement readBin and
writeBin which read and write C-style zero-terminated
character strings. They are for strings of known length, and
can optionally write an end-of-string mark. They are intended only
for character strings valid in the current locale.
If con is a character string, the functions call
file to obtain an file connection which is opened for
the duration of the function call.
If the connection is open it is read/written from its current position. If it is not open, it is opened for the duration of the call and then closed again. Connections can be open in either text or binary mode.
If readChar is called with con a raw vector, the data in
the vector is used as input. If writeChar is called with
con a raw vector, it is just an indication that a raw vector
should be returned.
In a single-byte locale, character strings containing ASCII
nul(s) will be read correctly by readChar and appear
with embedded nuls in the character vector returned. This may not
work for multi-byte locales, and does not work for writeChar.
If the character length requested for readChar is longer than
the data available on the connection, what is available is
returned. For writeChar if too many characters are requested
the output is zero-padded, with a warning.
Missing strings are written as NA.
Value
For readChar, a character vector of length the number of
items read (which might be less than length(nchars)).
For writeChar, a raw vector (if con is a raw vector) or
invisibly NULL.
See Also
The R Data Import/Export manual.
connections, readLines,
writeLines, readBin
Examples
## test fixed-length strings
zz <- file("testchar", "wb")
x <- c("a", "this will be truncated", "abc")
nc <- c(3, 10, 3)
writeChar(x, zz, nc, eos=NULL)
writeChar(x, zz, eos="\r\n")
close(zz)
zz <- file("testchar", "rb")
readChar(zz, nc)
readChar(zz, nchar(x)+3) # need to read the terminator explicitly
close(zz)
unlink("testchar")