readBin                 package: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)

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"'.

       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 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.

Details:

     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.  The connection must be open or
     open-able 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 '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.  Input strings are limited to 10000 characters.
      'readChar' and 'writeChar' can be used to read and write
     fixed-length strings.

     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 'writeBin', a raw vector (if 'con' is a raw vector) or
     invisibly 'NULL'.

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'.

     If '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.

See Also:

     The _R Data Import/Export_ manual.

     'readChar' to read/write fixed-length strings.

     '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)

     ## 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())
     rawToChar(z)
     readBin(z, character(), 4)

