命令名：

binary -
Insert and extract fields from binary strings

命令概要：

binary formatformatString?arg arg ...?

binary scanstring formatString?varName varName ...?

命令描述：（scan有点像format的逆过程）

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

Thebinary formatcommand generates a binary string whose layout is specified by theformatStringand whose contents come from the additional arguments. The resulting binary value is returned.

TheformatStringconsists 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 numericcount. Most field specifiers consume one argument to obtain the value to be formatted. The type character specifies how the value is to be formatted. Thecounttypically indicates how many items of the specified type are taken from the value. If present, thecountis 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 forbinary format.

Here is a small example to clarify the relation between the field specifiers and the arguments:

binary formatd3d {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 countin 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 converttocommand 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 arghas fewer than countbytes, then additional zero bytes are used to pad out the field. If argis longer than the specified length, the extra characters will be ignored. If countis *, then all of the bytes in argwill be formatted. If countis omitted, then one character will be formatted. For example,

binary formata7a*a alpha bravo charlie

will return a string equivalent toalpha\000\000bravoc,

binary formata* [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 formata* [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 formata* \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 aexcept that spaces are used for padding instead of nulls. For example,

binary formatA6A*A alpha bravo charlie

will returnalpha bravoc.

b

Stores a string of countbinary digits in low-to-high order within each byte in the output string. Argmust contain a sequence of 1and 0characters. The resulting bytes are emitted in first to last order with the bits being formatted in low-to-high order within each byte. If arghas fewer than countdigits, then zeros will be used for the remaining bits. If arghas more than the specified number of digits, the extra digits will be ignored. If countis *, then all of the digits in argwill be formatted. If countis 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 formatb5b* 11100 111000011010

will return a string equivalent to\x07\x87\x05.

B

This form is the same as bexcept that the bits are stored in high-to-low order within each byte. For example,

binary formatB5B* 11100 111000011010

will return a string equivalent to\xe0\xe1\xa0.

H

Stores a string of counthexadecimal digits in high-to-low within each byte in the output string. Argmust 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 arghas fewer than countdigits, then zeros will be used for the remaining digits. If arghas more than the specified number of digits, the extra digits will be ignored. If countis *, then all of the digits in argwill be formatted. If countis 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 formatH3H*H2 ab DEF 987

will return a string equivalent to\xab\x00\xde\xf0\x98.

h

This form is the same as Hexcept that the digits are stored in low-to-high order within each byte. This is seldom required. For example,

binary formath3h*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 countis specified, then argmust consist of an integer value. If countis specified, argmust 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 countis *, 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 formatc3cc* {3 -3 128 1} 260 {2 5}

will return a string equivalent to\x03\xfd\x80\x04\x02\x05, whereas

binary formatc {2 5}

will generate an error.

s

This form is the same as cexcept 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 formats3 {3 -3 258 1}

will return a string equivalent to\x03\x00\xfd\xff\x02\x01.

S

This form is the same as sexcept that it stores one or more 16-bit integers in big-endian byte order in the output string. For example,

binary formatS3 {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 sand Sexcept 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 byteOrderelement of the tcl_platformarray.

i

This form is the same as cexcept 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 formati3 {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 iexcept that it stores one or more one or more 32-bit integers in big-endian byte order in the output string. For example,

binary formatI3 {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 numberor normal) is the same as iand Iexcept 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 byteOrderelement of the tcl_platformarray.

w

This form is the same as cexcept 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 formatw 7810179016327718216

will return the stringHelloTcl

W

This form is the same as wexcept that it stores one or more one or more 64-bit integers in big-endian byte order in the output string. For example,

binary formatWc 4785469626960341345 110

will return the stringBigEndian

m

This form (mnemonically the mirror of w) is the same as wand Wexcept 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 byteOrderelement of the tcl_platformarray.

f

This form is the same as cexcept 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 formatf2 {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 fexcept 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 rexcept that it stores the single-precision floating point numbers in big-endian order.

d

This form is the same as fexcept 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 formatd1 {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 dexcept 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 qexcept that it stores the double-precision floating point numbers in big-endian order.

x

Stores countnull bytes in the output string. If countis not specified, stores one null byte. If countis *, generates an error. This type does not consume an argument. For example,

binary formata3xa3x2a3 abc def ghi

will return a string equivalent toabc\000def\000\000ghi.

X

Moves the cursor back countbytes in the output string. If countis *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 countis omitted then the cursor is moved back one byte. This type does not consume an argument. For example,

binary formata3X*a3X2a3 abc def ghi

will returndghi.

@

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 countrefers 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 countis *, then the cursor is moved to the current end of the output string. If countis omitted, then an error will be generated. This type does not consume an argument. For example,

binary formata5@2a1@*a3@10a1 abcde f ghi j

will returnabfdeghi\000\000j.

binary scan

Thebinary scancommand parses fields from a binary string, returning the number of conversions performed.Stringgives the input bytes to be parsed (one byte per character, and characters not representable as a byte have their high bits chopped) andformatStringindicates how to parse it. EachvarNamegives the name of a variable; when a field is scanned fromstringthe result is assigned to the corresponding variable.

As withbinary format, theformatStringconsists 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 numericcount. 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. Thecounttypically indicates how many items of the specified type are taken from the data. If present, thecountis 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 andbinary scanreturns 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 withbinary formatshould 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 variablebytesis long enough) assigns a list of three integers to the variablefirstand assigns a single value to the variablesecond. Ifbytescontains fewer than 8 bytes (i.e. four 2-byte integers), no assignment tosecondwill be made, and ifbytescontains fewer than 6 bytes (i.e. three 2-byte integers), no assignment tofirstwill be made. Hence:

puts [binary scanabcdefg 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 isimportantto note that thec,s, andS(andiandIon 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 formats1 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 formats1 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 countis *, then all of the remaining bytes in stringwill be scanned into the variable. If countis omitted, then one byte will be scanned. All bytes scanned will be interpreted as being characters in the range \u0000-\u00ff so the encoding convertfromcommand will be needed if the string is not a binary string or a string encoded in ISO 8859-1. For example,

binary scanabcde\000fghi a6a10 var1 var2

will return1with the string equivalent toabcde\000stored invar1andvar2left unmodified, and

binary scan\342\202\254 a* var1 set var2 [encoding convertfrom utf-8 $var1]

will store a Euro-currency character invar2.

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 return1withabc efghistored invar1.

b

The data is turned into a string of countbinary 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 countis *, then all of the remaining bits in stringwill be scanned. If countis omitted, then one bit will be scanned. For example,

binary scan\x07\x87\x05 b5b* var1 var2

will return2with11100stored invar1and1110000110100000stored invar2.

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 return2with01110stored invar1and1000011100000101stored invar2.

H

The data is turned into a string of counthexadecimal 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 countis *, then all of the remaining hex digits in stringwill be scanned. If countis omitted, then one hex digit will be scanned. For example,

binary scan\x07\xC6\x05\x1f\x34 H3H* var1 var2

will return2with07cstored invar1and051f34stored invar2.

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 return2with706stored invar1and502143stored invar2.

Note that most code that wishes to parse the hexadecimal digits from multiple bytes in order should use the Hformat.

c

The data is turned into count8-bit signed integers and stored in the corresponding variable as a list. If countis *, then all of the remaining bytes in stringwill be scanned. If countis omitted, then one 8-bit integer will be scanned. For example,

binary scan\x07\x86\x05 c2c* var1 var2

will return2with7 -122stored invar1and5stored invar2. 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 count16-bit signed integers represented in little-endian byte order. The integers are stored in the corresponding variable as a list. If countis *, then all of the remaining bytes in stringwill be scanned. If countis omitted, then one 16-bit integer will be scanned. For example,

binary scan\x05\x00\x07\x00\xf0\xff s2s* var1 var2

will return2with5 7stored invar1and-16stored invar2. 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 sexcept that the data is interpreted as count16-bit signed integers represented in big-endian byte order. For example,

binary scan\x00\x05\x00\x07\xff\xf0 S2S* var1 var2

will return2with5 7stored invar1and-16stored invar2.

t

The data is interpreted as count16-bit signed integers represented in the native byte order of the machine running the Tcl script. It is otherwise identical to sand S. To determine what the native byte order of the machine is, refer to the byteOrderelement of the tcl_platformarray.

i

The data is interpreted as count32-bit signed integers represented in little-endian byte order. The integers are stored in the corresponding variable as a list. If countis *, then all of the remaining bytes in stringwill be scanned. If countis omitted, then one 32-bit integer will be scanned. For example,

set str \x05\x00\x00\x00\x07\x00\x00\x00\xf0\xff\xff\xffbinary scan$str i2i* var1 var2

will return2with5 7stored invar1and-16stored invar2. 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 Iexcept that the data is interpreted as count32-bit signed integers represented in big-endian byte order. For example,

set str \x00\x00\x00\x05\x00\x00\x00\x07\xff\xff\xff\xf0binary scan$str I2I* var1 var2

will return2with5 7stored invar1and-16stored invar2.

n

The data is interpreted as count32-bit signed integers represented in the native byte order of the machine running the Tcl script. It is otherwise identical to iand I. To determine what the native byte order of the machine is, refer to the byteOrderelement of the tcl_platformarray.

w

The data is interpreted as count64-bit signed integers represented in little-endian byte order. The integers are stored in the corresponding variable as a list. If countis *, then all of the remaining bytes in stringwill be scanned. If countis omitted, then one 64-bit integer will be scanned. For example,

set str \x05\x00\x00\x00\x07\x00\x00\x00\xf0\xff\xff\xffbinary scan$str wi* var1 var2

will return2with30064771077stored invar1and-16stored invar2. Note that the integers returned are signed and cannot be represented by Tcl as unsigned values.

W

This form is the same as wexcept that the data is interpreted as count64-bit signed integers represented in big-endian byte order. For example,

set str \x00\x00\x00\x05\x00\x00\x00\x07\xff\xff\xff\xf0binary scan$str WI* var1 var2

will return2with21474836487stored invar1and-16stored invar2.

m

The data is interpreted as count64-bit signed integers represented in the native byte order of the machine running the Tcl script. It is otherwise identical to wand W. To determine what the native byte order of the machine is, refer to the byteOrderelement of the tcl_platformarray.

f

The data is interpreted as countsingle-precision floating point numbers in the machine's native representation. The floating point numbers are stored in the corresponding variable as a list. If countis *, then all of the remaining bytes in stringwill be scanned. If countis 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 return1with1.6000000238418579stored invar1.

r

This form is the same as fexcept that the data is interpreted as countsingle-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 fexcept that the data is interpreted as countsingle-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 fexcept that the data is interpreted as countdouble-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 return1with1.6000000000000001stored invar1.

q

This form is the same as dexcept that the data is interpreted as countdouble-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 dexcept that the data is interpreted as countdouble-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 countbytes in string. If countis *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 countis 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 return1with0304stored invar1.

X

Moves the cursor back countbytes in string. If countis *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 countis 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 return2with1 2stored invar1and020304stored invar2.

@

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 countrefers to a position beyond the end of string, then the cursor is positioned after the last byte. If countis omitted, then an error will be generated. For example,

binary scan\x01\x02\x03\x04 c2@1H* var1 var2

will return2with1 2stored invar1and020304stored invar2.

Portability Issues

Ther,R,qandQconversions 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 byformat) 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:

procwriteString{channel string} { set data [encoding convertto utf-8 $string] puts -nonewline [binary formatIa* \ [string length $data] $data] }

This procedure reads a string from a channel that was written by the previously presentedwriteStringprocedure:

procreadString{channel} { if {![binary scan[read $channel 4] I length]} { error "missing length" } set data [read $channel $length] return [encoding convertfrom utf-8 $data] }