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  pro-
       duce  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  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.

       Here is a small example to clarify  the  relation  between
       the field specifiers 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 asso-
       ciated with the  second  field  specifier.  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  char-
       acters:

       a    Stores a character string of length count in the out-
            put 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  format-
            ted.  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  dig-
            its,  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 con-
            sist 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  format-
            ted.   If the number of elements in the list is fewer
            than count, then an error is generated.  If the  num-
            ber  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 cur-
            sor  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 representation in the output string.
            This  representation is not portable across architec-
            tures, so it should not be used to communicate float-
            ing  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 represen-
            tation,  then  the value of FLT_MAX as defined by the
            system will be used instead.  Because Tcl  uses  dou-
            ble-precision   floating-point   numbers  internally,
            there may be some loss of precision in the conversion
            to  single-precision.  For example, on a Windows sys-
            tem 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 out-
            put  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 speci-
            fied 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 indi-
       cates 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  pre-
       sent,  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.

       A similar example as with binary format should explain the
       relation between field specifiers 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 vari-
       able  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 systems) will be scanned into long data size val-
       ues.   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  charac-
       ters:

       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 omit-
            ted, then one character will be scanned.  All charac-
            ters  scanned  will  be  interpreted  as being in the
            range \u0000-\u00ff so the encoding convertfrom  com-
            mand  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 dig-
            its 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  remain-
            ing  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 quanti-
            ties 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  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 converted to unsigned 16-bit  quanti-
            ties 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  repre-
            sented 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  inte-
            gers  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  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
            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  repre-
            sented 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  inte-
            gers  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  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  repre-
            sented 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 repre-
            sentation.  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-preci-
            sion floating point number will be scanned.  The size
            of  a floating point number may vary across architec-
            tures, so the number of bytes that  are  scanned  may
            vary.   If the data does not represent a valid float-
            ing 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 Pen-
            tium 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 posi-
            tion, 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 cur-
            sor  is  positioned after the last byte.  If count is
            omitted, then an error will be generated.  For  exam-
            ple,
                   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
