# R: Transfer Character Strings To and From Connections

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 `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.

### 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")

[Package base version 2.6.0 Index]