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OpenDarwin 7.2.1 - man page for binary (opendarwin section n)

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 values.	For example, given the values  16
       and  22,  on a 32 bit architecture, 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  for-
       matString  and  whose  contents	come from the additional arguments.  The resulting binary
       value is returned.

       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 value to be  for-
       matted.	 The  type character specifies how the value is to be formatted.  The count typi-
       cally 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 gener-
       ated.

       Here is a small example to clarify the relation between the field specifiers and the argu-
       ments:
	      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 asso-
       ciated field specifier, only the first three will be used. The second argument is  associ-
       ated  with  the second field specifier. The resulting binary string contains the four num-
       bers 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 charac-
	    ters \u0000-\u00ff, the encoding convertto command should be used first if this trun-
	    cation  is not desired (i.e. if the characters are not part of the ISO 8859-1 charac-
	    ter 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 digits.  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 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  speci-
	    fied, 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 generated.  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  lit-
	    tle-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  lit-
	    tle-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 inte-
	    gers 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  lit- |
	    tle-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 inte- |
	    gers 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-pre-
	    cision  floating  in  the machine's native representation in the output string.  This
	    representation is not portable across architectures, so it should not be used to com-
	    municate  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-pre-
	    cision  floating-point numbers internally, there may be some loss of precision 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-pre-
	    cision floating 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.

       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  argu-
	    ment.  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 cursor is positioned at location 0 so that
	    the  next byte stored will be the first byte in the result string.	If count is omit-
	    ted 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 posi-
	    tion beyond the last byte stored so far, then null bytes will be placed in the unini-
	    tialized 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 con-
       versions 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 spec-
       ifiers  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  variable  into which the scanned values 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 current 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.

       A  similar  example as with binary format should explain the relation between field speci-
       fiers and arguments in case of the binary scan subcommand:
	      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 inte-
       gers), 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  systems)  will  be
       scanned	into  long  data size values.  In doing this, values 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 variable.	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  repre-
	    sented  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 remain-
	    ing 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 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  inte-
	    gers  returned  are  signed,  but  they can be converted to unsigned 8-bit quantities
	    using an expression like:
		   expr ( $num + 0x100 ) % 0x100

       s    The data is interpreted as count 16-bit signed integers represented 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
	    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, but they can be converted to unsigned 16-bit quantities using an
	    expression like:
		   expr ( $num + 0x10000 ) % 0x10000

       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 represented 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
	    omitted, 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 and cannot be represented by Tcl as unsigned values.

       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 represented 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 |
	    omitted, 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 corre-
	    sponding 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  dependent.   For	example,  on a Windows system running on an Intel Pentium
	    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-preci-
	    sion 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 posi-
	    tioned 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 positioned 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 exam-
	    ple,
		   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 specified by count.
	    Note that position 0 refers to the first byte in string.  If count refers to a  posi-
	    tion 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 formatting or scanning integers.

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

KEYWORDS
       binary, format, scan

Tcl					       8.0					binary(n)


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