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

______________________________________________________________________________

NAME
       binary - Insert and extract fields from binary strings

SYNOPSIS
       binary format formatString ?arg arg ...?
       binary scan string formatString ?varName varName ...?
_________________________________________________________________

DESCRIPTION
       This  command  provides	facilities  for manipulating binary data.  The
       first form, 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 second form of the command,
       binary scan, does the opposite: it extracts data from a	binary	string
       and returns it as ordinary Tcl string values.

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 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.

       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 character string of length count in  the  output  string.
	    Every character is taken as modulo 256 (i.e. the low byte of every
	    character is used, and the high byte discarded)  so	 when  storing
	    character  strings	not  wholly  expressible  using the characters
	    \u0000-\u00ff, the encoding convertto command should be used first
	    if	this truncation 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 formatted.  If count is omitted, then one character
	    will be formatted.	For example,
		   binary format a7a*a alpha bravo charlie
	    will return a string equivalent to alpha\000\000bravoc.

       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 low-to-high 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 low-to-high 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* AB def
	    will return a string equivalent to \xba\x00\xed\x0f.

       H    This form is the same as h except that the digits  are  stored  in
	    high-to-low order within each byte.	 For example,
		   binary format H3H* ab DEF
	    will return a string equivalent to \xab\x00\xde\xf0.

       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;
	    otherwise  arg  must  consist  of a list containing at least count
	    integer elements.  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 fewer than count, then an error is gener‐
	    ated.  If the number of elements  in  the  list  is	 greater  than
	    count, then the extra elements 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.

       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

       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

       f    This form is the same as c except that it stores one or  more  one
	    or	more  single-precision floating in the machine's native repre‐
	    sentation in the output string.  This representation is not porta‐
	    ble	 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 overflows 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 pre‐
	    cision in the conversion to single-precision.  For example,	 on  a
	    Windows system running on an Intel Pentium processor,
		   binary format f2 {1.6 3.4}
	    will	return	      a	      string	   equivalent	    to
	    \xcd\xcc\xcc\x3f\x9a\x99\x59\x40.

       d    This form is the same as f except that it stores one or  more  one
	    or	more  double-precision floating in the machine's native repre‐
	    sentation 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.

       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 to be
       parsed 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 variable.

       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  numeric
       count.	Most field specifiers consume one argument to obtain the vari‐
       able into which the scanned values should be placed.  The type  charac‐
       ter specifies how the binary data is to be interpreted.	The count typ‐
       ically 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 current field specifier, then the corre‐
       sponding 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 argu‐
       ments, then an error is generated.

       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 $signShort s1 val; # val == 0xFFFF8000
       If  you want to produce an unsigned value, then you can mask the return
       value to the desired size.  For example, to produce an  unsigned	 short
       value:
	      set val [expr {$val & 0xFFFF}]; # val == 0x8000

       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 character 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  character  will  be
	    scanned.   All  characters scanned will be interpreted as being in
	    the range \u0000-\u00ff so the encoding convertfrom command	 might
	    be needed if the string is not an ISO 8859-1 string.  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.

       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'' charac‐
	    ters.  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
	    low-to-high 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  low-to-high	 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\x86\x05 h3h* var1 var2
	    will return 2 with 706 stored in var1 and 50 stored in var2.

       H    This form is the same as h, except the digits are taken  in	 high-
	    to-low order within each byte.  For example,
		   binary scan \x07\x86\x05 H3H* var1 var2
	    will return 2 with 078 stored in var1 and 05 stored in var2.

       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:
		   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:
		   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.

       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,
		   binary scan \x05\x00\x00\x00\x07\x00\x00\x00\xf0\xff\xff\xff 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:
		   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,
		   binary scan \x00\x00\x00\x05\x00\x00\x00\x07\xff\xff\xff\xf0 I2I* var1 var2
	    will return 2 with 5 7 stored in var1 and -16 stored in var2.

       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,	       │
		   binary scan \x05\x00\x00\x00\x07\x00\x00\x00\xf0\xff\xff\xff 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,						       │
		   binary scan \x00\x00\x00\x05\x00\x00\x00\x07\xff\xff\xff\xf0 WI* var1 var2│
	    will return 2 with 21474836487 stored in var1 and  -16  stored  in │
	    var2.

       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.

       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.

       x    Moves the cursor forward count bytes in string.  If count is *  or
	    is larger than the number of bytes after the current cursor cursor
	    position, 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.

PLATFORM ISSUES
       Sometimes it is desirable to format  or	scan  integer  values  in  the
       native  byte  order for the machine.  Refer to the byteOrder element of
       the tcl_platform array to decide which type character to use when  for‐
       matting or scanning integers.

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]
	      }

SEE ALSO
       format(n), scan(n), tclvars(n)

KEYWORDS
       binary, format, scan

Tcl				      8.0			     binary(n)
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