readBin: Transfer Binary Data To and From Connections

Description

Read binary data from or write binary data to a connection or raw vector.

Usage

readBin(con, what, n = 1L, size = NA_integer_, signed = TRUE, endian = .Platform$endian)
writeBin(object, con, size = NA_integer_, endian = .Platform$endian, useBytes = FALSE)

Arguments

con

A connection object or a character string naming a file or a raw vector.

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", "raw".

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_integer_, uses the natural size. Size changing is not supported for raw and 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.

useBytes

See writeLines.

Value

For readBin, a vector of appropriate mode and length the number of items read (which might be less than n).For writeBin, a raw vector (if con is a raw vector) or invisibly NULL.

Details

These functions are intended to be used with binary-mode connections. If con is a character string, the functions call file to obtain a binary-mode 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 in an appropriate mode (binary read or write) and then closed again. An open connection must be in binary mode.

If readBin is called with con a raw vector, the data in the vector is used as input. If writeBin is called with con a raw vector, it is just an indication that a raw vector should be returned.

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 NAs, and the extended precision sizes are unlikely to be portable across platforms.

readBin and writeBin read and write C-style zero-terminated character strings. Input strings are limited to 10000 characters. readChar and writeChar can be used to read and write fixed-length strings. No check is made that the string is valid in the current locale's encoding.

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

Only $2^31 - 1$ bytes can be written in a single call (and that is the maximum capacity of a raw vector on 32-bit platforms).

‘Endian-ness’ is relevant for size > 1, and should always be set for portable code (the default is only appropriate when writing and then reading files on the same platform).

Examples

Run this code

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)

## 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")

## use of raw
z <- writeBin(pi^{1:5}, raw(), size = 4)
readBin(z, numeric(), 5, size = 4)
z <- writeBin(c("a", "test", "of", "character"), raw())
readBin(z, character(), 4)

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