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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
       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
       flag character followed by an optional numeric count.  Most field specifiers  consume  one
       argument  to obtain the value to be formatted.  The type character specifies how the value
       is to be formatted.  The count typically indicates how many items of  the  specified  type
       are  taken  from the value.  If present, the count is a non-negative decimal integer or *,
       which normally 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. The  flag  character  is  ignored  for  for  binary
       format.

       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
       associated 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 characters:

       a    Stores a byte string of length count in the output string.  Every character is  taken
            as  modulo  256  (i.e.  the  low  byte  of every 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 to
            change the string into an external representation 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 formatted.  For example,
                   binary format a7a*a alpha bravo charlie
            will return a string equivalent to alpha\000\000bravoc,
                   binary format a* [encoding convertto utf-8 \u20ac]
            will return a string equivalent to \342\202\254 (which is the UTF-8 byte sequence for
            a Euro-currency character) and
                   binary format a* [encoding convertto iso8859-15 \u20ac]
            will return a string equivalent to \244 (which is the ISO 8859-15 byte sequence for a
            Euro-currency character). Contrast these last two with:
                   binary format a* \u20ac
            which  returns a string equivalent to \254 (i.e. \xac) by truncating the high-bits of
            the character, and which is probably not what is desired.

       A    This form is the same as a except that spaces are used for padding instead of  nulls.
            For example,
                   binary format A6A*A alpha bravo charlie
            will return alpha bravoc.

       b    Stores  a  string of count binary digits in low-to-high order within each byte in the
            output 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 high-to-low 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 high-to-low 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*H2 ab DEF 987
            will return a string equivalent to \xab\x00\xde\xf0\x98.

       h    This form is the same as H except that the digits are  stored  in  low-to-high  order
            within each byte. This is seldom required. For example,
                   binary format h3h*h2 AB def 987
            will return a string equivalent to \xba\x00\xed\x0f\x89.

       c    Stores  one  or  more  8-bit  integer  values  in  the output string.  If no count is
            specified, then arg must consist of an integer value. If count is specified, arg must
            consist  of  a  list  containing at least that many integers. The low-order 8 bits of
            each integer are stored as a one-byte value at the cursor position.  If count  is  *,
            then  all of the integers in the list are formatted. If the number of elements in the
            list is greater than count, then the 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.

       t    This form (mnemonically tiny) is the same as s and S except that it stores the 16-bit │
            integers  in  the output string in the native byte order of the machine where the Tcl │
            script is running.  To determine what the native byte order of the machine is,  refer │
            to the byteOrder element of the tcl_platform array.

       i    This  form  is  the  same  as  c except that it stores one or more 32-bit integers in
            little-endian byte order in the output string.  The low-order 32-bits of each integer
            are  stored  as  a  four-byte value at the cursor position with the least significant
            byte stored first.  For example,
                   binary format i3 {3 -3 65536 1}
            will return a 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

       n    This  form  (mnemonically  number  or  normal)  is the same as i and I except that it │
            stores the 32-bit integers in the output string in  the  native  byte  order  of  the │
            machine  where the Tcl script is running.  To determine what the native byte order of │
            the machine is, refer to the byteOrder element of the tcl_platform array.

       w    This form is the same as c except that it stores  one  or  more  64-bit  integers  in
            little-endian byte order in the output string.  The low-order 64-bits of each integer
            are stored as an eight-byte value at the cursor position with the  least  significant
            byte stored first.  For example,
                   binary format w 7810179016327718216
            will return the 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

       m    This form (mnemonically the mirror of w) is the same as w and W except that it stores │
            the  64-bit  integers  in  the  output string in the native byte order of the machine │
            where the Tcl script is running.  To determine what the  native  byte  order  of  the │
            machine is, refer to the byteOrder element of the tcl_platform array.

       f    This  form  is  the  same  as c except that it stores one or more one or more single-
            precision floating point numbers in the machine's native representation in the output
            string.   This  representation is not portable across architectures, so it should not
            be used to communicate floating point numbers across the  network.   The  size  of  a
            floating  point number may vary across architectures, so the number of bytes that are
            generated may vary.  If the value 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.

       r    This form (mnemonically real) is the same as f except  that  it  stores  the  single- │
            precision  floating  point  numbers  in  little-endian  order.   This conversion only │
            produces meaningful output when used on machines which use the  IEEE  floating  point │
            representation (very common, but not universal.)

       R    This  form is the same as r except that it stores the single-precision floating point │
            numbers in big-endian order.

       d    This form is the same as f except that it stores one or  more  one  or  more  double-
            precision floating point numbers in the machine's native representation in the output
            string.  For example, on a Windows system running on an Intel Pentium processor,
                   binary format d1 {1.6}
            will return a string equivalent to \x9a\x99\x99\x99\x99\x99\xf9\x3f.

       q    This form (mnemonically the mirror of d) is the same as d except that it  stores  the │
            double-precision floating point numbers in little-endian order.  This conversion only │
            produces meaningful output when used on machines which use the  IEEE  floating  point │
            representation (very common, but not universal.)

       Q    This  form is the same as q except that it stores the double-precision floating point │
            numbers in big-endian order.

       x    Stores count null bytes in the output string.  If count is not specified, stores  one
            null  byte.   If  count  is  *,  generates  an  error.  This type does not consume an
            argument.  For example,
                   binary format a3xa3x2a3 abc def ghi
            will return a 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
            uninitialized  locations and the cursor will be placed at the specified location.  If
            count is *, then the cursor is moved to the current end of  the  output  string.   If
            count  is  omitted,  then  an error will be generated.  This type does not consume an
            argument. For example,
                   binary format a5@2a1@*a3@10a1 abcde f ghi j
            will return abfdeghi\000\000j.

BINARY SCAN

       The binary scan command parses fields from  a  binary  string,  returning  the  number  of
       conversions performed.  String gives the input bytes to be parsed (one byte per character,
       and characters not representable as a byte have their high bits chopped) and  formatString
       indicates  how  to  parse  it.  Each varName gives the name of a variable; when a field is
       scanned from string the result is assigned to the corresponding 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 flag 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. The flag character “u” may be given to cause some types to be read as  unsigned
       values. The flag is accepted for all field types but is ignored for non-integer fields.

       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 variable
       second.  If bytes contains fewer than 8 bytes (i.e. four 2-byte integers),  no  assignment
       to  second  will  be  made,  and  if  bytes contains fewer than 6 bytes (i.e. three 2-byte
       integers), no assignment to first will be made.  Hence:
              puts [binary scan abcdefg s3s first second]
              puts $first
              puts $second
       will print (assuming neither variable is set previously):
              1
              25185 25699 26213
              can't read "second": no such variable

       It is important to note that the c, s, and S (and i  and  I  on  64bit  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 require unsigned values you can include the “u” flag character following the field
       type. For example, to read an unsigned short value:
              set signShort [binary format s1 0x8000]
              binary scan $signShort su1 val; # val == 0x00008000

       Each type-count pair moves an imaginary cursor through the binary data, reading bytes from
       the current position.  The cursor is initially at position 0 at the beginning of the data.
       The type may be any one of the following characters:

       a    The data is a byte string of length count.  If count is *, then all of the  remaining
            bytes  in  string  will  be scanned into the variable.  If count is omitted, then one
            byte will be scanned.  All bytes scanned will be interpreted as being  characters  in
            the  range  \u0000-\u00ff  so  the encoding convertfrom command will be needed if the
            string is not a binary string or a string encoded in ISO 8859-1.  For example,
                   binary scan abcde\000fghi a6a10 var1 var2
            will return 1 with the string equivalent to abcde\000 stored in var1  and  var2  left
            unmodified, and
                   binary scan \342\202\254 a* var1
                   set var2 [encoding convertfrom utf-8 $var1]
            will store a Euro-currency character in var2.

       A    This  form  is  the same as a, except trailing blanks and nulls are stripped from the
            scanned value before it is stored in the 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  high-to-low  order
            represented  as  a  sequence  of  characters in the set “0123456789abcdef”.  The data
            bytes are scanned in first to last order with the hex digits being taken in  high-to-
            low  order within each byte. Any extra bits in the last byte are ignored. If count is
            *, then all of the remaining hex digits in  string  will  be  scanned.  If  count  is
            omitted, then one hex digit will be scanned. For example,
                   binary scan \x07\xC6\x05\x1f\x34 H3H* var1 var2
            will return 2 with 07c stored in var1 and 051f34 stored in var2.

       h    This  form  is  the  same  as H, except the digits are taken in reverse (low-to-high)
            order within each byte. For example,
                   binary scan \x07\x86\x05\x12\x34 h3h* var1 var2
            will return 2 with 706 stored in var1 and 502143 stored in var2.
       Note that most code that wishes to parse the hexadecimal digits  from  multiple  bytes  in
       order should use the H format.

       c    The  data  is turned into count 8-bit signed integers and stored in the corresponding
            variable as a list. 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:
                   set num [expr { $num & 0xff }]

       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:
                   set num [expr { $num & 0xffff }]

       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.

       t    The  data  is  interpreted  as count 16-bit signed integers represented in the native │
            byte order of the machine running the Tcl script.  It is otherwise identical to s and │
            S.  To determine what the native byte order of the machine is, refer to the byteOrder │
            element of the tcl_platform array.

       i    The data is interpreted as count 32-bit signed integers 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,
                   set str \x05\x00\x00\x00\x07\x00\x00\x00\xf0\xff\xff\xff
                   binary scan $str i2i* var1 var2
            will return 2 with 5 7 stored in var1 and -16 stored in var2.  Note that the integers
            returned are signed, but they can be converted to unsigned 32-bit quantities using an
            expression like:
                   set num [expr { $num & 0xffffffff }]

       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,
                   set str \x00\x00\x00\x05\x00\x00\x00\x07\xff\xff\xff\xf0
                   binary scan $str I2I* var1 var2
            will return 2 with 5 7 stored in var1 and -16 stored in var2.

       n    The data is interpreted as count 32-bit signed integers  represented  in  the  native │
            byte order of the machine running the Tcl script.  It is otherwise identical to i and │
            I.  To determine what the native byte order of the machine is, refer to the byteOrder │
            element of the tcl_platform array.

       w    The  data is interpreted as count 64-bit signed integers 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,
                   set str \x05\x00\x00\x00\x07\x00\x00\x00\xf0\xff\xff\xff
                   binary scan $str wi* var1 var2
            will return 2 with 30064771077 stored in var1 and -16 stored in var2.  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,
                   set str \x00\x00\x00\x05\x00\x00\x00\x07\xff\xff\xff\xf0
                   binary scan $str WI* var1 var2
            will return 2 with 21474836487 stored in var1 and -16 stored in var2.

       m    The data is interpreted as count 64-bit signed integers  represented  in  the  native │
            byte order of the machine running the Tcl script.  It is otherwise identical to w and │
            W.  To determine what the native byte order of the machine is, refer to the byteOrder │
            element of the tcl_platform array.

       f    The  data  is  interpreted  as  count  single-precision floating point numbers in the
            machine's native representation.  The  floating  point  numbers  are  stored  in  the
            corresponding  variable as a list.  If count is *, then all of the remaining bytes in
            string will be scanned.  If count is  omitted,  then  one  single-precision  floating
            point  number  will  be scanned.  The size of a floating point number may vary across
            architectures, so the number of bytes that are scanned may vary.  If  the  data  does
            not  represent  a  valid  floating point number, the resulting value is undefined and
            compiler 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.

       r    This  form  is  the  same  as  f except that the data is interpreted as count single- │
            precision floating point number in  little-endian  order.   This  conversion  is  not │
            portable to the minority of systems not using IEEE floating point representations.

       R    This  form  is  the  same  as  f except that the data is interpreted as count single- │
            precision floating point number in big-endian order.  This conversion is not portable │
            to the minority of systems not using IEEE floating point representations.

       d    This  form  is  the  same  as  f except that the data is interpreted as count double-
            precision floating point numbers in the machine's 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.

       q    This  form  is  the  same  as  d except that the data is interpreted as count double- │
            precision floating point number in  little-endian  order.   This  conversion  is  not │
            portable to the minority of systems not using IEEE floating point representations.

       Q    This  form  is  the  same  as  d except that the data is interpreted as count double- │
            precision floating point number in big-endian order.  This conversion is not portable │
            to the minority of systems not using IEEE floating point representations.

       x    Moves  the cursor forward count bytes in string.  If count is * or is larger than the
            number of bytes after the current cursor 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.

PORTABILITY ISSUES

       The  r,  R,  q  and  Q  conversions  will only work reliably for transferring data between
       computers which are all using IEEE floating point representations.  This is  very  common,
       but not universal.  To transfer floating-point numbers portably between all architectures,
       use their textual representation (as produced by format) instead.

EXAMPLES

       This is a procedure to write a Tcl string  to  a  binary-encoded  channel  as  UTF-8  data
       preceded by a length word:
              proc writeString {channel string} {
                  set data [encoding convertto utf-8 $string]
                  puts -nonewline [binary format Ia* \
                          [string length $data] $data]
              }

       This  procedure reads a string from a channel that was written by the previously presented
       writeString procedure:
              proc readString {channel} {
                  if {![binary scan [read $channel 4] I length]} {
                      error "missing length"
                  }
                  set data [read $channel $length]
                  return [encoding convertfrom utf-8 $data]
              }

SEE ALSO

       format(3tcl), scan(3tcl), tclvars(3tcl)

KEYWORDS

       binary, format, scan