binary 命令

binary----由二进制字符串中插入，提取字段

语法:
binary format formatString ?arg arg ...?
binary scan string formatString ?varName varName ...?

该命令为操作二进制数据提供了手段。
第一种方式，binary format，通过一般的tcl值创建二进制字符串。比如，在32-bit平台上，给定两个值16和22,使用该命令可以产生一个由两个4字节的整形数组成的8字节的二进制字符串。
第二种方式，binary scan，作相反操作:其将从二进制字符串中除去出来数据并以一般的tcl字符串值返回

binary的转换类型:
a
 A character string of length count. Padded with nulls in binary format.
 binary format a7a5a alpha bravo charlie
 ====>alpha\000\000bravoc
 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
 A character string of length count. Padded with spaces in binary format. Trailing nulls and blanks are discarded in binary scan.
 binary format A6A*A alpha bravo charlie
 ====>alpha bravoc
 binary scan "abc efghi  \000" A* var1
 ====>will return 1 with abc efghi stored in var1.
b
 A binary string of length count. Low-to-high order.
 binary format b5b* 11100 111000011010
 ====>\x07\x87\x05
 binary format b* 11100000
 
 binary scan \x07\x87\x05 b5b* var1 var2
 will return 2 with 11100 stored in var1 and 1110000110100000 stored in var2.
B
 A binary string of length count. High-to-low order.
 binary format B5B* 11100 111000011010
 ====>\xe0\xe1\xa0
 binary scan \x70\x87\x05 B5B* var1 var2
 will return 2 with 01110 stored in var1 and 1000011100000101 stored in var2.
h
 A hexadecimal string of length count. Low-to-high order.
 binary format h3h* AB def
 ====>\xba\x00\xed\x0f
 binary scan \x07\x86\x05 h3h* var1 var2
 will return 2 with 706 stored in var1 and 50 stored in var2.
H
 A hexadecimal string of length count. High-to-low order. (More commonly used than h.)
 binary format H3H* ab DEF
 ====>\xab\x00\xde\xf0
 binary scan \x07\x86\x05 H3H* var1 var2
 will return 2 with 078 stored in var1 and 05 stored in var2.
c
 An 8-bit character code. The count is for repetition.
 binary format c3cc* {3 -3 128 1} 260 {2 5}
 ====>\x03\xfd\x80\x04\x02\x05
 binary format c {2 5}
 ====>提示错误
 
 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 & 0xff }
s
 A 16-bit integer in little-endian byte order. The count is for repetition.
 binary format s3 {3 -3 258 1}
 ====>\x03\x00\xfd\xff\x02\x01
 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 & 0xffff }
S
 A 16-bit integer in big-endian byte order. The count is for repetition.
 binary format S3 {3 -3 258 1}
 ====>\x00\x03\xff\xfd\x01\x02
 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
 A 32-bit integer in little-endian byte order. The count is for repetition.
 binary format i3 {3 -3 65536 1}
 ====>\x03\x00\x00\x00\xfd\xff\xff\xff\x00\x00\x01\x00
 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, but they can be converted to unsigned 32-bit quantities using an expression like:
 expr { $num & 0xffffffff }
I
 A 32-bit integer in big-endian byte order. The count is for repetition.
 binary format I3 {3 -3 65536 1}
 ====>\x00\x00\x00\x03\xff\xff\xff\xfd\x00\x01\x00\x00
 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
 A 64-bit integer in little-endian byte order. The count is for repetition. (Tcl 8.4)
 binary format w 7810179016327718216
 ====>HelloTcl
 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
 A 64-bit integer in big-endian byte order. The count is for repetition. (Tcl 8.4)
 binary format Wc 4785469626960341345 110
 ====>BigEndian
 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
 Single-precision floating point value in native format.The count is for repetition.
 binary format f2 {1.6 3.4}
 ====>\xcd\xcc\xcc\x3f\x9a\x99\x59\x40
 binary scan \x3f\xcc\xcc\xcd f var1
 will return 1 with 1.6000000238418579 stored in var1.
d
 Double-precision floating point value in native format. The count is for repetition.
 binary format d1 {1.6}
 ====>\x9a\x99\x99\x99\x99\x99\xf9\x3f
 binary scan \x9a\x99\x99\x99\x99\x99\xf9\x3f d var1
 will return 1 with 1.6000000000000001 stored in var1.
x
 Pack count null bytes with binary format.
 binary format a3xa3x2a3 abc def ghi
 ====>abc\000def\000\000ghi
 Skip count bytes with binary scan.
 binary scan \x01\x02\x03\x04 x2H* var1
 will return 1 with 0304 stored in var1.
X
 Backup count bytes.
 binary format a3X*a3X2a3 abc def ghi
 ====>dghi
 binary scan \x01\x02\x03\x04 c2XH* var1 var2
 will return 2 with 1 2 stored in var1 and 020304 stored in var2.
@
 Skip to absolute position specified by count. If count is *, skip to the end.
 binary format a5@2a1@*a3@10a1 abcde f ghi j
 ====>abfdeghi\000\000j
 binary scan \x01\x02\x03\x04 c2@1H* var1 var2
 will return 2 with 1 2 stored in var1 and 020304 stored in var2.
 
 
举例:
This is a procedure to write a Tcl string to a binary-encoded channel as UTF-8 data preceded by a length word:

proc writeString {channel string} {
    set data [encoding convertto utf-8 $string]
    puts -nonewline [binary format Ia* \
            [string length $data] $data]
}

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

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