readChar {base}R Documentation

Transfer Character Strings To and From Connections


Transfer character strings to and from connections, without assuming they are null-terminated on the connection.


readChar(con, nchars)

writeChar(object, con,
          nchars = nchar(object, type="chars"), eos = "")


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 nchars.
eos ‘end of string’: character string . The terminator to be written after each string, followed by an ASCII nul; use NULL for no terminator at all.


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.


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


## 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")

zz <- file("testchar", "rb")
readChar(zz, nc)
readChar(zz, nchar(x)+3) # need to read the terminator explicitly

[Package base version 2.5.0 Index]