Skip site navigation (1)Skip section navigation (2)

FreeBSD Manual Pages

  
 
  

home | help
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 en-
       coding,	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 bi-
       nary 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 ar-
	      bitrarily	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 indi-
       cates 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
	    formatted.	 If  count is omitted, then one	character will be for-
	    matted.  For example, the command:

		   binary format a7a*a alpha bravo charlie

	    will return	a binary string	equivalent to:

		   alpha\000\000bravoc

	    the	command:

		   binary format a* [encoding convertto	utf-8 \u20ac]

	    will return	a binary string	equivalent to:

		   \342\202\254

	    (which is the UTF-8	byte sequence for a Euro-currency  character),
	    and	the command:

		   binary format a* [encoding convertto	iso8859-15 \u20ac]

	    will return	a binary string	equivalent to:

		   \244

	    (which  is the ISO 8859-15 byte sequence for a Euro-currency char-
	    acter). Contrast these last	two with:

		   binary format a* \u20ac

	    which returns a binary string equivalent to:

		   \254

	    (i.e. \xac)	by truncating 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	binary string.	Arg must contain a se-
	    quence 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 re-
	    maining bits of the	last byte will be zeros.  For example,

		   binary format b5b* 11100 111000011010

	    will return	a binary 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 binary string	equivalent to:

		   \xe0\xe1\xa0

       H    Stores  a string of	count hexadecimal digits in high-to-low	within
	    each byte in the output binary string.  Arg	 must  contain	a  se-
	    quence of characters in the	set "0123456789abcdefABCDEF".  The re-
	    sulting bytes are emitted in first to last order with the hex dig-
	    its	being formatted	in high-to-low order within each byte.	If arg
	    has	fewer than count digits, then zeros will be used for  the  re-
	    maining digits.  If	arg has	more than the specified	number of dig-
	    its, 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  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 binary 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 binary 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 ex-
	    tra	elements are ignored.  For example,

		   binary format c3cc* {3 -3 128 1} 260	{2 5}

	    will return	a binary 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 binary 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 binary 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 de-
	    termine 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 binary 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 binary 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 binary 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 binary 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 binary 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-en-
	    dian  order.  This conversion only produces	meaningful output when
	    used on machines which use the IEEE	floating point	representation
	    (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 binary 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 binary 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
	    cursor 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  con-
	    sume 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
	    generated.	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  ig-
       nored for non-integer fields.

       A similar example as with binary	format should explain the relation be-
       tween field specifiers and arguments in case of the binary scan subcom-
       mand:

	      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  as-
       signs  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,  or  as  unsigned  if	 u  is
	    placed  immediately	 after the c. If count is "*", then all	of the
	    remaining bytes in string will be scanned.	If count  is  omitted,
	    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 unless cu in  place  of
	    c.

       s    The	 data  is  interpreted	as count 16-bit	signed integers	repre-
	    sented in little-endian byte order,	or as unsigned if u is	placed
	    immediately	 after	the  s.	 The integers are stored in the	corre-
	    sponding variable as a list.  If count is "*", then	all of the re-
	    maining  bytes  in	string	will be	scanned.  If count is omitted,
	    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 unless su is used in
	    place of s.

       S    This form is the same as s except that the data is interpreted  as
	    count  16-bit  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, or as unsigned if u	is placed immediately after the	t.  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,	or as unsigned if u is	placed
	    immediately	 after	the  i.	 The integers are stored in the	corre-
	    sponding variable as a list.  If count is "*", then	all of the re-
	    maining  bytes  in	string	will be	scanned.  If count is omitted,
	    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 unless iu is used in
	    place of i.

       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,
	    or as unsigned if u	is placed immediately after the	I.  For	 exam-
	    ple,

		   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, or as unsigned if u	is placed immediately after the	n.  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, or as unsigned	if u is	placed
	    immediately	after the w.  The integers are stored  in  the	corre-
	    sponding variable as a list.  If count is "*", then	all of the re-
	    maining bytes in string will be scanned.   If  count  is  omitted,
	    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.

       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,
	    or as unsigned if u	is placed immediately after the	W.  For	 exam-
	    ple,

		   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, or as unsigned if u	is placed immediately after the	m.  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  or-
	    der.   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 us-
	    ing	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 na-
	    tive  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 or-
	    der.  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 us-
	    ing	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 po-
	    sition, 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  ex-
	    ample,

		   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 po-
	    sitioned  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 ar-
	    gument.  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)

NAME | SYNOPSIS | DESCRIPTION | BINARY ENCODE AND DECODE | BINARY FORMAT | BINARY SCAN | PORTABILITY ISSUES | EXAMPLES | SEE ALSO | KEYWORDS

Want to link to this manual page? Use this URL:
<https://www.freebsd.org/cgi/man.cgi?query=binary.tcl87&manpath=FreeBSD+13.0-RELEASE+and+Ports>

home | help