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binary

binary(n)                    Tcl Built-In Commands                   binary(n)



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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 ...?
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DESCRIPTION
       This  command  provides  facilities  for manipulating binary data.  The
       first form, binary format, creates a binary string from normal Tcl val-
       ues.   For  example,  given the values 16 and 22, on a 32 bit architec-
       ture, 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  addi-
       tional arguments.  The resulting binary value is returned.

       The  formatString  consists  of a sequence of zero or more field speci-
       fiers separated by zero or more spaces.  Each field specifier is a sin-
       gle  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 dig-
            its.  If arg has more than the specified  number  of  digits,  the
            extra digits will be ignored.  If count is *, then all of the dig-
            its 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  gener-
            ated.   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  repre-
            sentation  in  the  output  string.   This  representation  is not
            portable across architectures, so it should not be used to  commu-
            nicate  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 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 system running on an Intel  Pentium  proces-
            sor,
                   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 repre-
            sentation 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 cur-
            sor 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 gener-
            ated.  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 vari-
       able into which the scanned values should be placed.  The type  charac-
       ter specifies how the binary data is to be interpreted.  The count typ-
       ically 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 corre-
       sponding 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 argu-
       ments, then an error is generated.

       It is important to note that the c, s, and S (and i and I on 64bit sys-
       tems)  will be scanned into long data size values.  In doing this, val-
       ues 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  vari-
            able.  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''  charac-
            ters.   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  omit-
            ted, 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  con-
            verted to unsigned 8-bit quantities using an expression like:
                   expr ( $num + 0x100 ) % 0x100

       s    The  data  is  interpreted  as count 16-bit signed integers repre-
            sented 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  con-
            verted 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 repre-
            sented 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  repre-
            sented 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 depen-
            dent.  For example, on a Windows system running on an  Intel  Pen-
            tium 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  posi-
            tioned  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 spec-
            ified  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  for-
       matting or scanning integers.


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


KEYWORDS
       binary, format, scan



Tcl                                   8.0                            binary(n)