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, 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 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 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.

       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.   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  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 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 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

       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 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  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
            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-precision 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 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  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 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
            unitialized 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  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
       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.

       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.   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 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 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 integers 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 \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.

       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  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-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 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 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 specified 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 formatting or scanning
       integers.


SEE ALSO
       format, scan, tclvars


KEYWORDS
