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 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\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\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} 257 {2 5}
will return a string equivalent to
\x03\xfd\x80\x01\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\x10\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\x10\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
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 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.
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 exam-
ple,
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 low-to-high 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