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, cre-ates creates
ates 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 numeric count. Most
field specifiers consume one argument to obtain the value to be formatted. The type character speci-fies specifies
fies 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.
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 character 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 encod-ing encoding
ing convertto command should be used first if this truncation is not desired (i.e. if the char-acters characters
acters 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.
A This form is the same as a except that spaces are used for padding instead of nulls. For exam-ple, example,
ple,
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 lowto-high
to-high order within each byte. If arg has fewer than count digits, then zeros will be used for
the remaining digits. If arg has more than the specified number of digits, the extra digits
will be ignored. If count is *, then all of the digits in arg will be formatted. If count is
omitted, then one digit will be formatted. If the number of digits formatted does not end at a
byte boundary, the remaining bits of the last byte will be zeros. For example,
binary format h3h* AB def
will return a string equivalent to \xba\x00\xed\x0f.
H This form is the same as h except that the digits are stored in high-to-low order within each
byte. For example,
binary format H3H* ab DEF
will return a string equivalent to \xab\x00\xde\xf0.
c Stores one or more 8-bit integer values in the output string. If no count is specified, then
arg must consist of an integer value; otherwise arg must consist of a list containing at least
count integer elements. The low-order 8 bits of each integer are stored as a one-byte value at
the cursor position. If count is *, then all of the integers in the list are formatted. If the
number of elements in the list is fewer than count, then an error is generated. If the number
of elements in the list is greater than count, then the extra elements are ignored. For exam-ple, example,
ple,
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 fourbyte
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 bigendian
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 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
f This form is the same as c except that it stores one or more one or more single-precision float-ing floating
ing 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 repre-sentation, representation,
sentation, 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 Pen-tium Pentium
tium 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 float-ing floating
ing in the machine's native representation in the output string. For example, on a Windows sys-tem system
tem running on an Intel Pentium processor,
binary format d1 {1.6}
will return a string equivalent to \x9a\x99\x99\x99\x99\x99\xf9\x3f.
x Stores count null bytes in the output string. If count is not specified, stores one null byte.
If count is *, generates an error. This type does not consume an argument. For example,
binary format a3xa3x2a3 abc def ghi
will return a string equivalent to abc\000def\000\000ghi.
X Moves the cursor back count bytes in the output string. If count is * or is larger than the
current cursor position, then the cursor is positioned at location 0 so that the next byte
stored will be the first byte in the result string. If count is omitted then the cursor is
moved back one byte. This type does not consume an argument. For example,
binary format a3X*a3X2a3 abc def ghi
will return dghi.
@ Moves the cursor to the absolute location in the output string specified by count. Position 0
refers to the first byte in the output string. If count refers to a position beyond the last
byte stored so far, then null bytes will be placed in the uninitialized locations and the cursor
will be placed at the specified location. If count is *, then the cursor is moved to the cur-rent current
rent 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 per-formed. performed.
formed. String gives the input to be parsed and formatString indicates how to parse it. Each var-Name varName
Name 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 sepa-rated separated
rated by zero or more spaces. Each field specifier is a single type character followed by an
optional numeric count. Most field specifiers consume one argument to obtain the variable into which
the scanned values should be placed. The type character specifies how the binary data is to be
interpreted. The count typically indicates how many items of the specified type are taken from the
data. If present, the count is a non-negative decimal integer or *, which normally indicates that
all of the remaining items in the data are to be used. If there are not enough bytes left after the
current cursor position to satisfy the current field specifier, then the corresponding variable is
left untouched and binary scan returns immediately with the number of variables that were set. If
there are not enough arguments for all of the fields in the format string that consume arguments,
then an error is generated.
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 $signShort s1 val; # val == 0xFFFF8000
If you want to produce an unsigned value, then you can mask the return value to the desired size.
For example, to produce an unsigned short value:
set val [expr {$val & 0xFFFF}]; # val == 0x8000
Each type-count pair moves an imaginary cursor through the binary data, reading bytes from the cur-rent current
rent 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. All characters scanned will be interpreted as being in the range \u0000-\u00ff so the
encoding convertfrom command 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 digits in low-to-high order represented as a
sequence of ``1'' and ``0'' characters. The data bytes are scanned in first to last order with
the bits being taken in low-to-high order within each byte. Any extra bits in the last byte are
ignored. If count is *, then all of the remaining bits in string will be scanned. If count is
omitted, then one bit will be scanned. For example,
binary scan \x07\x87\x05 b5b* var1 var2
will return 2 with 11100 stored in var1 and 1110000110100000 stored in var2.
B This form is the same as b, except the bits are taken in high-to-low order within each byte.
For example,
binary scan \x70\x87\x05 B5B* var1 var2
will return 2 with 01110 stored in var1 and 1000011100000101 stored in var2.
h The data is turned into a string of count hexadecimal digits in low-to-high order represented as
a sequence of characters in the set ``0123456789abcdef''. The data bytes are scanned in first
to last order with the hex digits being taken in low-to-high order within each byte. Any extra
bits in the last byte are ignored. If count is *, then all of the remaining hex digits in
string will be scanned. If count is omitted, then one hex digit will be scanned. For example,
binary scan \x07\x86\x05 h3h* var1 var2
will return 2 with 706 stored in var1 and 50 stored in var2.
H This form is the same as h, except the digits are taken in high-to-low order within each byte.
For example,
binary scan \x07\x86\x05 H3H* var1 var2
will return 2 with 078 stored in var1 and 05 stored in var2.
c The data is turned into count 8-bit signed integers and stored in the corresponding variable as
a list. If count is *, then all of the remaining bytes in string will be scanned. If count is
omitted, then one 8-bit integer will be scanned. For example,
binary scan \x07\x86\x05 c2c* var1 var2
will return 2 with 7 -122 stored in var1 and 5 stored in var2. Note that the integers returned
are signed, but they can be converted to unsigned 8-bit quantities using an expression like:
expr ( $num + 0x100 ) % 0x100
s The data is interpreted as count 16-bit signed integers represented in little-endian byte order.
The integers are stored in the corresponding variable as a list. If count is *, then all of the
remaining bytes in string will be scanned. If count is omitted, then one 16-bit integer will be
scanned. For example,
binary scan \x05\x00\x07\x00\xf0\xff s2s* var1 var2
will return 2 with 5 7 stored in var1 and -16 stored in var2. Note that the integers returned
are signed, but they can be converted to unsigned 16-bit quantities using an expression like:
expr ( $num + 0x10000 ) % 0x10000
S This form is the same as s except that the data is interpreted as count 16-bit signed integers
represented in big-endian byte order. For example,
binary scan \x00\x05\x00\x07\xff\xf0 S2S* var1 var2
will return 2 with 5 7 stored in var1 and -16 stored in var2.
i The data is interpreted as count 32-bit signed integers represented in little-endian byte order.
The integers are stored in the corresponding variable as a list. If count is *, then all of the
remaining bytes in string will be scanned. If count is omitted, then one 32-bit integer will be
scanned. For example,
binary scan \x05\x00\x00\x00\x07\x00\x00\x00\xf0\xff\xff\xff i2i* var1 var2
will return 2 with 5 7 stored in var1 and -16 stored in var2. Note that the integers returned
are signed and cannot be represented by Tcl as unsigned values.
I This form is the same as I except that the data is interpreted as count 32-bit signed integers
represented in big-endian byte order. For example,
binary 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 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, |
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 |
represented 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
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 com-piler compiler
piler 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 float-ing floating
ing point numbers in the machine's native representation. For example, on a Windows system run-ning running
ning on an Intel Pentium processor,
binary scan \x9a\x99\x99\x99\x99\x99\xf9\x3f d var1
will return 1 with 1.6000000000000001 stored in var1.
x Moves the cursor forward count bytes in string. If count is * or is larger than the number of
bytes after the current cursor cursor position, then the cursor is positioned after the last
byte in string. If count is omitted, then the cursor is moved forward one byte. Note that this
type does not consume an argument. For example,
binary scan \x01\x02\x03\x04 x2H* var1
will return 1 with 0304 stored in var1.
X Moves the cursor back count bytes in string. If count is * or is larger than the current cursor
position, then the cursor is positioned at location 0 so that the next byte scanned will be the
first byte in string. If count is omitted then the cursor is moved back one byte. Note that
this type does not consume an argument. For example,
binary scan \x01\x02\x03\x04 c2XH* var1 var2
will return 2 with 1 2 stored in var1 and 020304 stored in var2.
@ Moves the cursor to the absolute location in the data string specified by count. Note that
position 0 refers to the first byte in string. If count refers to a position beyond the end of
string, then the cursor is positioned after the last byte. If count is omitted, then an error
will be generated. For example,
binary scan \x01\x02\x03\x04 c2@1H* var1 var2
will return 2 with 1 2 stored in var1 and 020304 stored in var2.
PLATFORM ISSUES
Sometimes it is desirable to format or scan integer values in the native byte order for the machine.
Refer to the byteOrder element of the tcl_platform array to decide which type character to use when
formatting or scanning integers.
SEE ALSO
format(n), scan(n), tclvars(n)
KEYWORDS
binary, format, scan
Tcl 8.0 binary(n)
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