R: Transfer Binary Data To and From Connections

readBin {base} | R Documentation

## Transfer Binary Data To and From Connections

### Description

Read binary data from a connection, or write binary data to a connection.

### Usage

    readBin(con, what, n = 1, size = NA, signed = TRUE,
            endian = .Platform$endian)
    writeBin(object, con, size = NA, endian = .Platform$endian)

    readChar(con, nchars)
    writeChar(object, con, nchars = nchar(object), eos = "")

### Arguments

`con` | A connection object or a character string.
`what` | Either an object whose mode will give the mode of the vector to be read, or a character vector of length one describing the mode: one of `"numeric", "double", "integer", "int", "logical", "complex", "character"`.
`n` | integer. The (maximal) number of records to be read. You can use an over-estimate here, but not too large as storage is reserved for `n` items.
`size` | integer. The number of bytes per element in the byte stream. The default, `NA`, uses the natural size. Size changing is not supported for complex vectors.
`signed` | logical. Only used for integers of sizes 1 and 2, when it determines if the quantity on file should be regarded as a signed or unsigned integer.
`endian` | The endian-ness (`"big"` or `"little"` of the target system for the file. Using `"swap"` will force swapping endian-ness.
`object` | An R object to be written to the connection.
`nchars` | integer, giving the lengths of (unterminated) character strings to be read or written.
`eos` | character. The terminator to be written after each string, followed by an ASCII `nul`; use `NULL` for no terminator at all.

### Details

If the `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.

If `size` is specified and not the natural size of the object, each element of the vector is coerced to an appropriate type before being written or as it is read. Possible sizes are 1, 2, 4 and possibly 8 for integer or logical vectors, and 4, 8 and possibly 12/16 for numeric vectors. (Note that coercion occurs as signed types except if `signed = FALSE` when reading integers of sizes 1 and 2.) Changing sizes is unlikely to preserve `NA`s, and the extended precision sizes are unlikely to be portable across platforms.

`readBin` and `writeBin` read and write C-style zero-terminated character strings. `readChar` and `writeChar` allow more flexibility, and can also be used on text-mode connections.

Handling R's missing and special (`Inf`, `-Inf` and `NaN` values is discussed in the R Data Import/Export manual.

### Value

For `readBin`, a vector of appropriate mode and length the number of items read (which might be less than `n`).
For `readChar`, a character vector of length the number of items read (which might be less than `length(nchars)`).
For `writeBin` and `writeChar`, none.

### Note

Integer read/writes of size 8 will be available if either C type `long` is of size 8 bytes or C type `long long` exists and is of size 8 bytes.

Real read/writes of size `sizeof(long double)` (usually 12 or 16 bytes) will be available only if that type is available and different from `double`.

Note that as R character strings cannot contain ASCII `nul`, strings read by `readChar` which contain such characters will appear to be shorted than requested, but the additional bytes are read from the file.

If the character length requested for `readChar` is longer than the string, as from version 1.4.0 what is available is returned.

### See Also

The R Data Import/Export manual.

`connections`, `readLines`, `writeLines`.

`.Machine` for the sizes of `long`, `long long` and `long double`.

### Examples

    zz <- file("testbin", "wb")
    writeBin(1:10, zz)
    writeBin(pi, zz, endian="swap")
    writeBin(pi, zz, size=4)
    writeBin(pi^2, zz, size=4, endian="swap")
    writeBin(pi+3i, zz)
    writeBin("A test of a connection", zz)
    z <- paste("A very long string", 1:100, collapse=" + ")
    writeBin(z, zz)
    if(.Machine$sizeof.long == 8 || .Machine$sizeof.longlong == 8)
        writeBin(as.integer(5^(1:10)), zz, size = 8)
    if((s <-.Machine$sizeof.longdouble) > 8) writeBin((pi/3)^(1:10), zz, size = s)
    close(zz)

    zz <- file("testbin", "rb")
    readBin(zz, integer(), 4)
    readBin(zz, integer(), 6)
    readBin(zz, numeric(), 1, endian="swap")
    readBin(zz, numeric(), size=4)
    readBin(zz, numeric(), size=4, endian="swap")
    readBin(zz, complex(), 1)
    readBin(zz, character(), 1)
    z2 <- readBin(zz, character(), 1)
    if(.Machine$sizeof.long == 8 || .Machine$sizeof.longlong == 8)
        readBin(zz, integer(), 10,  size = 8)
    if((s <-.Machine$sizeof.longdouble) > 8) readBin(zz, numeric(), 10, size = s)
    close(zz)
    unlink("testbin")
    stopifnot(z2 == z)

    ## test fixed-length strings
    zz <- file("testbin", "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("testbin", "rb")
    readChar(zz, nc)
    readChar(zz, nchar(x)+3) # need to read the terminator explicitly
    close(zz)
    unlink("testbin")

    ## signed vs unsigned ints
    zz <- file("testbin", "wb")
    x <- as.integer(seq(0, 255, 32))
    writeBin(x, zz, size=1)
    writeBin(x, zz, size=1)
    x <- as.integer(seq(0, 60000, 10000))
    writeBin(x, zz, size=2)
    writeBin(x, zz, size=2)
    close(zz)
    zz <- file("testbin", "rb")
    readBin(zz, integer(), 8, size=1)
    readBin(zz, integer(), 8, size=1, signed=FALSE)
    readBin(zz, integer(), 7, size=2)
    readBin(zz, integer(), 7, size=2, signed=FALSE)
    close(zz)
    unlink("testbin")

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