- NAME
- binary - Insert and extract fields from binary strings
- SYNOPSIS
- binary format formatString ?arg arg ...?
- binary scan string formatString ?varName varName ...?
- DESCRIPTION
- BINARY FORMAT
- a
- A
- b
- B
- h
- H
- c
- s
- S
- i
- I
- f
- d
- x
- X
- @
- BINARY SCAN
- a
- A
- b
- B
- h
- H
- c
- s
- S
- i
- I
- f
- d
- x
- X
- @
- PLATFORM ISSUES
- SEE ALSO
- KEYWORDS
binary - Insert and extract fields from binary strings
binary format formatString ?arg arg ...?
binary scan string formatString ?varName varName ...?
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.
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 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 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 example,
binary format c3cc* {3 -3 128 1} 260 {2 5}
will return a string equivalent to
\x03\xfd\x80\x04\x02\x05, whereas
binary format c {2 5}
will generate an error.
- s
-
This form is the same as c except that it stores one or more
16-bit integers in little-endian byte order in the output string. The
low-order 16-bits of each integer are stored as a two-byte value at
the cursor position with the least significant byte stored first. For
example,
binary format s3 {3 -3 258 1}
will return a string equivalent to
\x03\x00\xfd\xff\x02\x01.
- S
-
This form is the same as s except that it stores one or more
16-bit integers in big-endian byte order in the output string. For
example,
binary format S3 {3 -3 258 1}
will return a string equivalent to
\x00\x03\xff\xfd\x01\x02.
- i
-
This form is the same as c except that it stores one or more
32-bit integers in little-endian byte order in the output string. The
low-order 32-bits of each integer are stored as a four-byte value at
the cursor position with the least significant byte stored first. For
example,
binary format i3 {3 -3 65536 1}
will return a string equivalent to
\x03\x00\x00\x00\xfd\xff\xff\xff\x00\x00\x01\x00
- I
-
This form is the same as i except that it stores one or more one
or more 32-bit integers in big-endian byte order in the output string.
For example,
binary format I3 {3 -3 65536 1}
will return a string equivalent to
\x00\x00\x00\x03\xff\xff\xff\xfd\x00\x01\x00\x00
- f
-
This form is the same as c except that it stores one or more one
or more single-precision floating in the machine's native
representation in the output string. This representation is not
portable across 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.
- 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 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
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.
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 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.
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 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 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 \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 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 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.
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.
format, scan, tclvars
binary, format, scan
Copyright © 1997 by Sun Microsystems, Inc.
Copyright © 1995-1997 Roger E. Critchlow Jr.