src/library/base/man/readBin.Rd

% File src/library/base/man/readBin.Rd
% Part of the R package, https://www.R-project.org
% Copyright 1995-2018 R Core Team
% Distributed under GPL 2 or later

\name{readBin}
\alias{readBin}
\alias{writeBin}
\title{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{
  \item{con}{A \link{connection} object or a character string naming a file or
    a raw vector.}
  \item{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 \code{"numeric"}, \code{"double"},
    \code{"integer"}, \code{"int"}, \code{"logical"}, \code{"complex"},
    \code{"character"}, \code{"raw"}.}
  \item{n}{numeric.  The (maximal) number of records to be
    read.  You can use an over-estimate here, but not too large as
    storage is reserved for \code{n} items.}
  \item{size}{integer.  The number of bytes per element in the byte
    stream.  The default, \code{NA_integer_}, uses the natural size.
    Size changing is not supported for raw and complex vectors.}
  \item{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.}
  \item{endian}{The endian-ness (\code{"big"} or \code{"little"}) of the
    target system for the file.  Using \code{"swap"} will force swapping
    endian-ness.}
  \item{object}{An \R object to be written to the connection.}
  \item{useBytes}{See \code{\link{writeLines}}.}
}
\details{
  These functions can only be used with binary-mode connections.
  If \code{con} is a character string, the functions call
  \code{\link{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 \code{readBin} is called with \code{con} a raw vector, the data in
  the vector is used as input.  If \code{writeBin} is called with
  \code{con} a raw vector, it is just an indication that a raw vector
  should be returned.

  If \code{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 \code{signed = FALSE} when reading integers of sizes 1 and 2.)
  Changing sizes is unlikely to preserve \code{NA}s, and the extended
  precision sizes are unlikely to be portable across platforms.

  \code{readBin} and \code{writeBin} read and write C-style
  zero-terminated character strings.  Input strings are limited to 10000
  characters.  \code{\link{readChar}} and \code{\link{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 (\code{Inf}, \code{-Inf} and
  \code{NaN}) values is discussed in the \sQuote{R Data Import/Export} manual.

  Only \eqn{2^{31}-1}{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).

  \sQuote{Endian-ness} is relevant for \code{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).
}

\note{
  Integer read/writes of size 8 will be available if either C type
  \code{long} is of size 8 bytes or C type \code{long long} exists and
  is of size 8 bytes.

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

  If \code{readBin(what = character())} is used incorrectly on a file
  which does not contain C-style character strings, warnings (usually
  many) are given.  From a file or connection, the input will be broken
  into pieces of length 10000 with any final part being discarded.
}

\value{
  For \code{readBin}, a vector of appropriate mode and length the number of
  items read (which might be less than \code{n}).

  For \code{writeBin}, a raw vector (if \code{con} is a raw vector) or
  invisibly \code{NULL}.
}
\seealso{
  The \sQuote{R Data Import/Export} manual.

  \code{readChar} to read/write fixed-length strings.

  \code{\link{connections}}, \code{\link{readLines}},
  \code{\link{writeLines}}.

  \code{\link{.Machine}} for the sizes of \code{long}, \code{long long}
  and \code{long double}.
}
\examples{
zzfil <- tempfile("testbin")
zz <- file(zzfil, "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(zzfil, "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(zzfil)
stopifnot(z2 == z)

## signed vs unsigned ints
zzfil <- tempfile("testbin")
zz <- file(zzfil, "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(zzfil, "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(zzfil)

## 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)
}
\keyword{file}
\keyword{connection}