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binary(n)		     Tcl Built-In Commands		     binary(n)

______________________________________________________________________________

NAME
       binary - Insert and extract fields from binary strings

SYNOPSIS
       binary decode format ?-option value ...? data			       │
       binary encode format ?-option value ...? data			       │
       binary format formatString ?arg arg ...?
       binary scan string formatString ?varName varName ...?
_________________________________________________________________

DESCRIPTION
       This  command  provides	facilities  for manipulating binary data.  The
       subcommand binary format creates a binary string from normal  Tcl  val‐
       ues.   For  example,  given the values 16 and 22, on a 32-bit architec‐
       ture, it might produce an 8-byte binary string consisting of two 4-byte
       integers,  one  for  each  of the numbers.  The subcommand binary scan,
       does the opposite: it extracts data from a binary string and returns it
       as  ordinary  Tcl  string  values.  The binary encode and binary decode │
       subcommands convert binary data to or from  string  encodings  such  as │
       base64 (used in MIME messages for example).

       Note that other operations on binary data, such as taking a subsequence
       of it, getting its length, or reinterpreting it as  a  string  in  some
       encoding,  are  done  by other Tcl commands (respectively string range,
       string length and encoding convertfrom in the example cases).  A binary
       string in Tcl is merely one where all the characters it contains are in
       the range \u0000-\u00FF.

BINARY ENCODE AND DECODE
       When encoding binary data as a readable	string,	 the  starting	binary │
       data  is passed to the binary encode command, together with the name of │
       the encoding to use and any  encoding-specific  options	desired.  Data │
       which  has  been	 encoded  can  be  converted back to binary form using │
       binary decode. The following formats and options are supported.	       │

       base64								       │
	      The base64 binary encoding is commonly used in mail messages and │
	      XML  documents, and uses mostly upper and lower case letters and │
	      digits. It has the distinction of being  able  to	 be  rewrapped │
	      arbitrarily without losing information.			       │

	      During encoding, the following options are supported:	       │

	      -maxlen length						       │
		     Indicates	that  the output should be split into lines of │
		     no more than length characters. By default, lines are not │
		     split.						       │

	      -wrapchar character					       │
		     Indicates	that,  when  lines  are	 split	because of the │
		     -maxlen option, character	should	be  used  to  separate │
		     lines. By default, this is a newline character, “\n”.     │

	      During decoding, the following options are supported:	       │

	      -strict							       │
		     Instructs	the decoder to throw an error if it encounters │
		     whitespace characters. Otherwise it ignores them.	       │

       hex								       │
	      The hex binary encoding converts each byte to a pair of hexadec‐ │
	      imal digits in big-endian form.				       │

	      No  options  are supported during encoding. During decoding, the │
	      following options are supported:				       │

	      -strict							       │
		     Instructs the decoder to throw an error if it  encounters │
		     whitespace characters. Otherwise it ignores them.	       │

       uuencode								       │
	      The  uuencode  binary encoding used to be common for transfer of │
	      data between Unix systems and on	USENET,	 but  is  less	common │
	      these  days, having been largely superseded by the base64 binary │
	      encoding.							       │

	      During encoding, the following  options  are  supported  (though │
	      changing	them  may  produce files that other implementations of │
	      decoders cannot process):					       │

	      -maxlen length						       │
		     Indicates that the output should be split into  lines  of │
		     no	 more  than  length  characters. By default, lines are │
		     split every 61 characters, and this must be in the	 range │
		     3 to 85 due to limitations in the encoding.	       │

	      -wrapchar character					       │
		     Indicates	that,  when  lines  are	 split	because of the │
		     -maxlen option, character	should	be  used  to  separate │
		     lines. By default, this is a newline character, “\n”.     │

	      During decoding, the following options are supported:	       │

	      -strict							       │
		     Instructs	the decoder to throw an error if it encounters │
		     unexpected whitespace characters.	Otherwise  it  ignores │
		     them.						       │

	      Note  that neither the encoder nor the decoder handle the header │
	      and footer of the uuencode format.			       │

BINARY FORMAT
       The binary format command generates a binary  string  whose  layout  is
       specified  by  the  formatString and whose contents come from the addi‐
       tional arguments.  The resulting binary value is returned.

       The formatString consists of a sequence of zero or  more	 field	speci‐
       fiers separated by zero or more spaces.	Each field specifier is a sin‐
       gle type character followed by an optional flag character  followed  by
       an  optional numeric count.  Most field specifiers consume one argument
       to obtain the value to be formatted.  The type character specifies  how
       the  value  is to be formatted.	The count typically indicates how many
       items of the specified type are taken from the value.  If present,  the
       count  is a non-negative decimal integer or *, which normally indicates
       that all of the items in the value are to be used.  If  the  number  of
       arguments does not match the number of fields in the format string that
       consume arguments, then an error is generated. The  flag	 character  is
       ignored for binary format.

       Here is a small example to clarify the relation between the field spec‐
       ifiers and the arguments:
	      binary format d3d {1.0 2.0 3.0 4.0} 0.1

       The first argument is a list of four numbers, but because of the	 count
       of  3  for the associated field specifier, only the first three will be
       used. The second argument is associated with the	 second	 field	speci‐
       fier.  The  resulting binary string contains the four numbers 1.0, 2.0,
       3.0 and 0.1.

       Each type-count pair moves an imaginary cursor through the binary data,
       storing	bytes at the current position and advancing the cursor to just
       after the last byte stored.  The cursor is initially at position	 0  at
       the  beginning  of  the data.  The type may be any one of the following
       characters:

       a    Stores a byte string of length count in the output string.	 Every
	    character is taken as modulo 256 (i.e. the low byte of every char‐
	    acter is used, and the high byte discarded) so when storing	 char‐
	    acter   strings   not  wholly  expressible	using  the  characters
	    \u0000-\u00ff, the encoding convertto command should be used first
	    to change the string into an external representation if this trun‐
	    cation is not desired (i.e. if the characters are not part of  the
	    ISO	 8859-1	 character  set.)   If arg has fewer than count bytes,
	    then additional zero bytes are used to pad out the field.  If  arg
	    is	longer than the specified length, the extra characters will be
	    ignored.  If count is *, then all of the bytes in arg will be for‐
	    matted.   If  count is omitted, then one character will be format‐
	    ted.  For example,
		   binary format a7a*a alpha bravo charlie
	    will return a string equivalent to alpha\000\000bravoc,
		   binary format a* [encoding convertto utf-8 \u20ac]
	    will return a string equivalent  to	 \342\202\254  (which  is  the
	    UTF-8 byte sequence for a Euro-currency character) and
		   binary format a* [encoding convertto iso8859-15 \u20ac]
	    will  return a string equivalent to \244 (which is the ISO 8859-15
	    byte sequence for a Euro-currency character). Contrast these  last
	    two with:
		   binary format a* \u20ac
	    which  returns a string equivalent to \254 (i.e. \xac) by truncat‐
	    ing the high-bits of the character, and which is probably not what
	    is desired.

       A    This form is the same as a except that spaces are used for padding
	    instead of nulls.  For example,
		   binary format A6A*A alpha bravo charlie
	    will return alpha bravoc.

       b    Stores a string of count binary digits in low-to-high order within
	    each  byte in the output string.  Arg must contain a sequence of 1
	    and 0 characters.  The resulting bytes are	emitted	 in  first  to
	    last  order	 with  the  bits  being formatted in low-to-high order
	    within each byte.  If arg has fewer than count digits, then	 zeros
	    will  be  used  for	 the remaining bits.  If arg has more than the
	    specified number of digits, the extra digits will be ignored.   If
	    count  is  *, then all of the digits in arg will be formatted.  If
	    count is omitted, then one digit will be formatted.	 If the number
	    of	bits  formatted does not end at a byte boundary, the remaining
	    bits of the last byte will be zeros.  For example,
		   binary format b5b* 11100 111000011010
	    will return a string equivalent to \x07\x87\x05.

       B    This form is the same as b except that  the	 bits  are  stored  in
	    high-to-low order within each byte.	 For example,
		   binary format B5B* 11100 111000011010
	    will return a string equivalent to \xe0\xe1\xa0.

       H    Stores  a string of count hexadecimal digits in high-to-low within
	    each byte in the output string.  Arg must contain  a  sequence  of
	    characters	in  the	 set  “0123456789abcdefABCDEF”.	 The resulting
	    bytes are emitted in first to last order with the hex digits being
	    formatted in high-to-low order within each byte.  If arg has fewer
	    than count digits, then zeros will be used for the remaining  dig‐
	    its.   If  arg  has	 more than the specified number of digits, the
	    extra digits will be ignored.  If count is *, then all of the dig‐
	    its in arg will be formatted.  If count is omitted, then one digit
	    will be formatted.	If the number of digits formatted does not end
	    at	a  byte	 boundary, the remaining bits of the last byte will be
	    zeros.  For example,
		   binary format H3H*H2 ab DEF 987
	    will return a string equivalent to \xab\x00\xde\xf0\x98.

       h    This form is the same as H except that the digits  are  stored  in
	    low-to-high	 order	within each byte. This is seldom required. For
	    example,
		   binary format h3h*h2 AB def 987
	    will return a string equivalent to \xba\x00\xed\x0f\x89.

       c    Stores one or more 8-bit integer values in the output string.   If
	    no	count is specified, then arg must consist of an integer value.
	    If count is specified, arg must consist of a  list	containing  at
	    least that many integers. The low-order 8 bits of each integer are
	    stored as a one-byte value at the cursor position.	If count is *,
	    then  all of the integers in the list are formatted. If the number
	    of elements in the list is greater than count, then the extra ele‐
	    ments are ignored.	For example,
		   binary format c3cc* {3 -3 128 1} 260 {2 5}
	    will  return  a  string  equivalent	 to  \x03\xfd\x80\x04\x02\x05,
	    whereas
		   binary format c {2 5}
	    will generate an error.

       s    This form is the same as c except  that  it	 stores	 one  or  more
	    16-bit  integers in little-endian byte order in the output string.
	    The low-order 16-bits of each integer are  stored  as  a  two-byte
	    value  at  the  cursor  position  with  the least significant byte
	    stored first.  For example,
		   binary format s3 {3 -3 258 1}
	    will return a string equivalent to \x03\x00\xfd\xff\x02\x01.

       S    This form is the same as s except  that  it	 stores	 one  or  more
	    16-bit  integers  in  big-endian  byte order in the output string.
	    For example,
		   binary format S3 {3 -3 258 1}
	    will return a string equivalent to \x00\x03\xff\xfd\x01\x02.

       t    This form (mnemonically tiny) is the same as s and S  except  that
	    it	stores	the 16-bit integers in the output string in the native
	    byte order of the machine where the Tcl  script  is	 running.   To
	    determine  what  the native byte order of the machine is, refer to
	    the byteOrder element of the tcl_platform array.

       i    This form is the same as c except  that  it	 stores	 one  or  more
	    32-bit  integers in little-endian byte order in the output string.
	    The low-order 32-bits of each integer are stored  as  a  four-byte
	    value  at  the  cursor  position  with  the least significant byte
	    stored first.  For example,
		   binary format i3 {3 -3 65536 1}
	    will       return	    a	    string	  equivalent	    to
	    \x03\x00\x00\x00\xfd\xff\xff\xff\x00\x00\x01\x00

       I    This  form	is the same as i except that it stores one or more one
	    or more 32-bit integers in big-endian byte	order  in  the	output
	    string.  For example,
		   binary format I3 {3 -3 65536 1}
	    will	return	      a	      string	   equivalent	    to
	    \x00\x00\x00\x03\xff\xff\xff\xfd\x00\x01\x00\x00

       n    This form (mnemonically number or normal) is the same as i	and  I
	    except  that it stores the 32-bit integers in the output string in
	    the native byte order of the machine where the Tcl script is  run‐
	    ning.   To determine what the native byte order of the machine is,
	    refer to the byteOrder element of the tcl_platform array.

       w    This form is the same as c except  that  it	 stores	 one  or  more
	    64-bit  integers in little-endian byte order in the output string.
	    The low-order 64-bits of each integer are stored as an  eight-byte
	    value  at  the  cursor  position  with  the least significant byte
	    stored first.  For example,
		   binary format w 7810179016327718216
	    will return the string HelloTcl

       W    This form is the same as w except that it stores one or  more  one
	    or	more  64-bit  integers	in big-endian byte order in the output
	    string.  For example,
		   binary format Wc 4785469626960341345 110
	    will return the string BigEndian

       m    This form (mnemonically the mirror of w) is the same as  w	and  W
	    except  that it stores the 64-bit integers in the output string in
	    the native byte order of the machine where the Tcl script is  run‐
	    ning.   To determine what the native byte order of the machine is,
	    refer to the byteOrder element of the tcl_platform array.

       f    This form is the same as c except that it stores one or  more  one
	    or	more  single-precision floating point numbers in the machine's
	    native representation in the output string.	  This	representation
	    is	not portable across architectures, so it should not be used to
	    communicate floating point numbers across the network.   The  size
	    of	a  floating point number may vary across architectures, so the
	    number of bytes that are generated may vary.  If the  value	 over‐
	    flows  the	machine's  native  representation,  then  the value of
	    FLT_MAX as defined by the system will be  used  instead.   Because
	    Tcl uses double-precision floating point numbers internally, there
	    may be some loss of precision in the conversion  to	 single-preci‐
	    sion.   For	 example, on a Windows system running on an Intel Pen‐
	    tium processor,
		   binary format f2 {1.6 3.4}
	    will       return	    a	    string	  equivalent	    to
	    \xcd\xcc\xcc\x3f\x9a\x99\x59\x40.

       r    This  form	(mnemonically  real)  is  the same as f except that it
	    stores the single-precision	 floating  point  numbers  in  little-
	    endian  order.   This  conversion  only produces meaningful output
	    when used on machines which use the IEEE floating point  represen‐
	    tation (very common, but not universal.)

       R    This form is the same as r except that it stores the single-preci‐
	    sion floating point numbers in big-endian order.

       d    This form is the same as f except that it stores one or  more  one
	    or	more  double-precision floating point numbers in the machine's
	    native representation in the output string.	  For  example,	 on  a
	    Windows system running on an Intel Pentium processor,
		   binary format d1 {1.6}
	    will	return	      a	      string	   equivalent	    to
	    \x9a\x99\x99\x99\x99\x99\xf9\x3f.

       q    This form (mnemonically the mirror of d) is the same as  d	except
	    that it stores the double-precision floating point numbers in lit‐
	    tle-endian order.  This conversion only produces meaningful output
	    when  used on machines which use the IEEE floating point represen‐
	    tation (very common, but not universal.)

       Q    This form is the same as q except that it stores the double-preci‐
	    sion floating point numbers in big-endian order.

       x    Stores  count  null	 bytes	in the output string.  If count is not
	    specified, stores one null byte.  If  count	 is  *,	 generates  an
	    error.  This type does not consume an argument.  For example,
		   binary format a3xa3x2a3 abc def ghi
	    will return a string equivalent to abc\000def\000\000ghi.

       X    Moves  the cursor back count bytes in the output string.  If count
	    is * or is larger than the current cursor position, then the  cur‐
	    sor	 is positioned at location 0 so that the next byte stored will
	    be the first byte in the result string.  If count is omitted  then
	    the	 cursor is moved back one byte.	 This type does not consume an
	    argument.  For example,
		   binary format a3X*a3X2a3 abc def ghi
	    will return dghi.

       @    Moves the cursor to the absolute location  in  the	output	string
	    specified  by  count.   Position 0 refers to the first byte in the
	    output string.  If count refers to a position beyond the last byte
	    stored so far, then null bytes will be placed in the uninitialized
	    locations and the cursor will be placed at the specified location.
	    If	count is *, then the cursor is moved to the current end of the
	    output string.  If count is omitted, then an error will be	gener‐
	    ated.  This type does not consume an argument. For example,
		   binary format a5@2a1@*a3@10a1 abcde f ghi j
	    will return abfdeghi\000\000j.

BINARY SCAN
       The  binary  scan command parses fields from a binary string, returning
       the number of conversions performed.  String gives the input  bytes  to
       be  parsed (one byte per character, and characters not representable as
       a byte have their high bits chopped) and formatString indicates how  to
       parse  it.   Each varName gives the name of a variable; when a field is
       scanned from string the result is assigned to the  corresponding	 vari‐
       able.

       As  with binary format, the formatString consists of a sequence of zero
       or more field specifiers separated by zero or more spaces.  Each	 field
       specifier is a single type character followed by an optional flag char‐
       acter followed by an optional numeric  count.   Most  field  specifiers
       consume one argument to obtain the variable into which the scanned val‐
       ues should be placed.  The type character specifies how the binary data
       is  to be interpreted.  The count typically indicates how many items of
       the specified type are taken from the data.  If present, the count is a
       non-negative decimal integer or *, which normally indicates that all of
       the remaining items in the data are to  be  used.   If  there  are  not
       enough bytes left after the current cursor position to satisfy the cur‐
       rent field specifier, then the corresponding variable is left untouched
       and  binary  scan returns immediately with the number of variables that
       were set.  If there are not enough arguments for all of the  fields  in
       the  format  string that consume arguments, then an error is generated.
       The flag character “u” may be given to cause some types to be  read  as
       unsigned	 values.  The  flag  is	 accepted  for	all field types but is
       ignored for non-integer fields.

       A similar example as with binary format	should	explain	 the  relation
       between	field specifiers and arguments in case of the binary scan sub‐
       command:
	      binary scan $bytes s3s first second

       This command (provided the binary string in the variable bytes is  long
       enough)	assigns	 a  list  of  three integers to the variable first and
       assigns a single value to the variable second.  If bytes contains fewer
       than  8 bytes (i.e. four 2-byte integers), no assignment to second will
       be made, and if bytes contains fewer than 6 bytes  (i.e.	 three	2-byte
       integers), no assignment to first will be made.	Hence:
	      puts [binary scan abcdefg s3s first second]
	      puts $first
	      puts $second
       will print (assuming neither variable is set previously):
	      1
	      25185 25699 26213
	      can't read "second": no such variable

       It is important to note that the c, s, and S (and i and I on 64bit sys‐
       tems) will be scanned into long data size values.  In doing this,  val‐
       ues  that  have	their high bit set (0x80 for chars, 0x8000 for shorts,
       0x80000000 for ints), will be sign extended.  Thus the  following  will
       occur:
	      set signShort [binary format s1 0x8000]
	      binary scan $signShort s1 val; # val == 0xFFFF8000
       If  you	require unsigned values you can include the “u” flag character
       following the field type. For example, to read an unsigned short value:
	      set signShort [binary format s1 0x8000]
	      binary scan $signShort su1 val; # val == 0x00008000

       Each type-count pair moves an imaginary cursor through the binary data,
       reading	bytes  from  the current position.  The cursor is initially at
       position 0 at the beginning of the data.	 The type may be  any  one  of
       the following characters:

       a    The	 data  is  a byte string of length count.  If count is *, then
	    all of the remaining bytes in string  will	be  scanned  into  the
	    variable.	If  count  is  omitted, then one byte will be scanned.
	    All bytes scanned will be interpreted as being characters  in  the
	    range  \u0000-\u00ff  so  the encoding convertfrom command will be
	    needed if the string is not a binary string or a string encoded in
	    ISO 8859-1.	 For example,
		   binary scan abcde\000fghi a6a10 var1 var2
	    will  return  1  with the string equivalent to abcde\000 stored in
	    var1 and var2 left unmodified, and
		   binary scan \342\202\254 a* var1
		   set var2 [encoding convertfrom utf-8 $var1]
	    will store a Euro-currency character in var2.

       A    This form is the same as a, except trailing blanks and  nulls  are
	    stripped  from  the scanned value before it is stored in the vari‐
	    able.  For example,
		   binary scan "abc efghi  \000" A* var1
	    will return 1 with abc efghi stored in var1.

       b    The data is turned into a string of count binary digits in low-to-
	    high  order	 represented  as a sequence of “1” and “0” characters.
	    The data bytes are scanned in first to last order  with  the  bits
	    being taken in low-to-high order within each byte.	Any extra bits
	    in the last byte are ignored.  If count is	*,  then  all  of  the
	    remaining  bits  in	 string will be scanned.  If count is omitted,
	    then one bit will be scanned.  For example,
		   binary scan \x07\x87\x05 b5b* var1 var2
	    will return 2 with	11100  stored  in  var1	 and  1110000110100000
	    stored in var2.

       B    This  form is the same as b, except the bits are taken in high-to-
	    low order within each byte.	 For example,
		   binary scan \x70\x87\x05 B5B* var1 var2
	    will return 2 with	01110  stored  in  var1	 and  1000011100000101
	    stored in var2.

       H    The	 data  is  turned into a string of count hexadecimal digits in
	    high-to-low order represented as a sequence of characters  in  the
	    set	 “0123456789abcdef”.   The  data bytes are scanned in first to
	    last order with the hex digits being taken	in  high-to-low	 order
	    within  each byte. Any extra bits in the last byte are ignored. If
	    count is *, then all of the remaining hex digits in string will be
	    scanned.  If count is omitted, then one hex digit will be scanned.
	    For example,
		   binary scan \x07\xC6\x05\x1f\x34 H3H* var1 var2
	    will return 2 with 07c stored in var1 and 051f34 stored in var2.

       h    This form is the same as H, except the digits are taken in reverse
	    (low-to-high) order within each byte. For example,
		   binary scan \x07\x86\x05\x12\x34 h3h* var1 var2
	    will return 2 with 706 stored in var1 and 502143 stored in var2.

	    Note  that	most  code that wishes to parse the hexadecimal digits
	    from multiple bytes in order should use the H format.

       c    The data is turned into count 8-bit signed integers and stored  in
	    the	 corresponding	variable as a list. If count is *, then all of
	    the remaining bytes in string will be scanned.  If count is	 omit‐
	    ted, then one 8-bit integer will be scanned.  For example,
		   binary scan \x07\x86\x05 c2c* var1 var2
	    will  return  2  with  7 -122 stored in var1 and 5 stored in var2.
	    Note that the integers returned are signed, but they can  be  con‐
	    verted to unsigned 8-bit quantities using an expression like:
		   set num [expr { $num & 0xff }]

       s    The	 data  is  interpreted	as count 16-bit signed integers repre‐
	    sented in little-endian byte order.	 The integers  are  stored  in
	    the	 corresponding variable as a list.  If count is *, then all of
	    the remaining bytes in string will be scanned.  If count is	 omit‐
	    ted, then one 16-bit integer will be scanned.  For example,
		   binary scan \x05\x00\x07\x00\xf0\xff s2s* var1 var2
	    will  return  2  with  5  7 stored in var1 and -16 stored in var2.
	    Note that the integers returned are signed, but they can  be  con‐
	    verted to unsigned 16-bit quantities using an expression like:
		   set num [expr { $num & 0xffff }]

       S    This  form is the same as s except that the data is interpreted as
	    count 16-bit signed integers represented in big-endian byte order.
	    For example,
		   binary scan \x00\x05\x00\x07\xff\xf0 S2S* var1 var2
	    will return 2 with 5 7 stored in var1 and -16 stored in var2.

       t    The	 data  is  interpreted	as count 16-bit signed integers repre‐
	    sented in the native byte order of the  machine  running  the  Tcl
	    script.   It is otherwise identical to s and S.  To determine what
	    the native byte order of the machine is, refer  to	the  byteOrder
	    element of the tcl_platform array.

       i    The	 data  is  interpreted	as count 32-bit signed integers repre‐
	    sented in little-endian byte order.	 The integers  are  stored  in
	    the	 corresponding variable as a list.  If count is *, then all of
	    the remaining bytes in string will be scanned.  If count is	 omit‐
	    ted, then one 32-bit integer will be scanned.  For example,
		   set str \x05\x00\x00\x00\x07\x00\x00\x00\xf0\xff\xff\xff
		   binary scan $str i2i* var1 var2
	    will  return  2  with  5  7 stored in var1 and -16 stored in var2.
	    Note that the integers returned are signed, but they can  be  con‐
	    verted to unsigned 32-bit quantities using an expression like:
		   set num [expr { $num & 0xffffffff }]

       I    This  form is the same as I except that the data is interpreted as
	    count 32-bit signed integers represented in big-endian byte order.
	    For example,
		   set str \x00\x00\x00\x05\x00\x00\x00\x07\xff\xff\xff\xf0
		   binary scan $str I2I* var1 var2
	    will return 2 with 5 7 stored in var1 and -16 stored in var2.

       n    The	 data  is  interpreted	as count 32-bit signed integers repre‐
	    sented in the native byte order of the  machine  running  the  Tcl
	    script.   It is otherwise identical to i and I.  To determine what
	    the native byte order of the machine is, refer  to	the  byteOrder
	    element of the tcl_platform array.

       w    The	 data  is  interpreted	as count 64-bit signed integers repre‐
	    sented in little-endian byte order.	 The integers  are  stored  in
	    the	 corresponding variable as a list.  If count is *, then all of
	    the remaining bytes in string will be scanned.  If count is	 omit‐
	    ted, then one 64-bit integer will be scanned.  For example,
		   set str \x05\x00\x00\x00\x07\x00\x00\x00\xf0\xff\xff\xff
		   binary scan $str wi* var1 var2
	    will  return  2  with 30064771077 stored in var1 and -16 stored in
	    var2.  Note that the integers returned are signed  and  cannot  be
	    represented by Tcl as unsigned values.

       W    This  form is the same as w except that the data is interpreted as
	    count 64-bit signed integers represented in big-endian byte order.
	    For example,
		   set str \x00\x00\x00\x05\x00\x00\x00\x07\xff\xff\xff\xf0
		   binary scan $str WI* var1 var2
	    will  return  2  with 21474836487 stored in var1 and -16 stored in
	    var2.

       m    The data is interpreted as count  64-bit  signed  integers	repre‐
	    sented  in	the  native  byte order of the machine running the Tcl
	    script.  It is otherwise identical to w and W.  To determine  what
	    the	 native	 byte  order of the machine is, refer to the byteOrder
	    element of the tcl_platform array.

       f    The data is interpreted as count single-precision  floating	 point
	    numbers  in	 the  machine's	 native	 representation.  The floating
	    point numbers are stored in the corresponding variable as a	 list.
	    If	count  is *, then all of the remaining bytes in string will be
	    scanned.  If count is omitted, then one single-precision  floating
	    point number will be scanned.  The size of a floating point number
	    may vary across architectures, so the number  of  bytes  that  are
	    scanned may vary.  If the data does not represent a valid floating
	    point number, the resulting value is undefined and compiler depen‐
	    dent.   For	 example, on a Windows system running on an Intel Pen‐
	    tium processor,
		   binary scan \x3f\xcc\xcc\xcd f var1
	    will return 1 with 1.6000000238418579 stored in var1.

       r    This form is the same as f except that the data is interpreted  as
	    count  single-precision  floating  point  number  in little-endian
	    order.  This conversion is not portable to the minority of systems
	    not using IEEE floating point representations.

       R    This  form is the same as f except that the data is interpreted as
	    count single-precision floating point number in big-endian	order.
	    This  conversion  is  not  portable to the minority of systems not
	    using IEEE floating point representations.

       d    This form is the same as f except that the data is interpreted  as
	    count  double-precision  floating  point  numbers in the machine's
	    native representation. For example, on a Windows system running on
	    an Intel Pentium processor,
		   binary scan \x9a\x99\x99\x99\x99\x99\xf9\x3f d var1
	    will return 1 with 1.6000000000000001 stored in var1.

       q    This  form is the same as d except that the data is interpreted as
	    count double-precision  floating  point  number  in	 little-endian
	    order.  This conversion is not portable to the minority of systems
	    not using IEEE floating point representations.

       Q    This form is the same as d except that the data is interpreted  as
	    count  double-precision floating point number in big-endian order.
	    This conversion is not portable to the  minority  of  systems  not
	    using IEEE floating point representations.

       x    Moves  the cursor forward count bytes in string.  If count is * or
	    is larger than the number of bytes after the current cursor	 posi‐
	    tion, then the cursor is positioned after the last byte in string.
	    If count is omitted, then the cursor is moved  forward  one	 byte.
	    Note that this type does not consume an argument.  For example,
		   binary scan \x01\x02\x03\x04 x2H* var1
	    will return 1 with 0304 stored in var1.

       X    Moves  the cursor back count bytes in string.  If count is * or is
	    larger than the current cursor position, then the cursor is	 posi‐
	    tioned  at	location  0  so that the next byte scanned will be the
	    first byte in string.  If count is	omitted	 then  the  cursor  is
	    moved  back	 one  byte.   Note  that this type does not consume an
	    argument.  For example,
		   binary scan \x01\x02\x03\x04 c2XH* var1 var2
	    will return 2 with 1 2 stored in var1 and 020304 stored in var2.

       @    Moves the cursor to the absolute location in the data string spec‐
	    ified  by count.  Note that position 0 refers to the first byte in
	    string.  If count refers to a position beyond the end  of  string,
	    then  the  cursor  is positioned after the last byte.  If count is
	    omitted, then an error will be generated.  For example,
		   binary scan \x01\x02\x03\x04 c2@1H* var1 var2
	    will return 2 with 1 2 stored in var1 and 020304 stored in var2.

PORTABILITY ISSUES
       The r, R, q and Q conversions will only work reliably for  transferring
       data  between  computers which are all using IEEE floating point repre‐
       sentations.  This is very  common,  but	not  universal.	  To  transfer
       floating-point  numbers	portably  between all architectures, use their
       textual representation (as produced by format) instead.

EXAMPLES
       This is a procedure to write a Tcl string to a  binary-encoded  channel
       as UTF-8 data preceded by a length word:

	      proc writeString {channel string} {
		  set data [encoding convertto utf-8 $string]
		  puts -nonewline [binary format Ia* \
			  [string length $data] $data]
	      }

       This  procedure	reads  a string from a channel that was written by the
       previously presented writeString procedure:

	      proc readString {channel} {
		  if {![binary scan [read $channel 4] I length]} {
		      error "missing length"
		  }
		  set data [read $channel $length]
		  return [encoding convertfrom utf-8 $data]
	      }

       This converts the contents of a file (named in the  variable  filename)
       to base64 and prints them:

	      set f [open $filename rb]
	      set data [read $f]
	      close $f
	      puts [binary encode base64 -maxlen 64 $data]

SEE ALSO
       encoding(n), format(n), scan(n), string(n), tcl_platform(n)

KEYWORDS
       binary, format, scan

Tcl				      8.0			     binary(n)
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