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 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.

       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.  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  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

       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 unitialized
            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.

       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.    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 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 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 \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 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, scan, tclvars


KEYWORDS
       binary, format, scan
