1binary(n) Tcl Built-In Commands binary(n)
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6
8 binary - Insert and extract fields from binary strings
9
11 binary decode format ?-option value ...? data │
12 binary encode format ?-option value ...? data │
13 binary format formatString ?arg arg ...?
14 binary scan string formatString ?varName varName ...?
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16
18 This command provides facilities for manipulating binary data. The
19 subcommand binary format creates a binary string from normal Tcl val‐
20 ues. For example, given the values 16 and 22, on a 32-bit architec‐
21 ture, it might produce an 8-byte binary string consisting of two 4-byte
22 integers, one for each of the numbers. The subcommand binary scan,
23 does the opposite: it extracts data from a binary string and returns it
24 as ordinary Tcl string values. The binary encode and binary decode │
25 subcommands convert binary data to or from string encodings such as │
26 base64 (used in MIME messages for example).
27 Note that other operations on binary data, such as taking a subsequence
29 of it, getting its length, or reinterpreting it as a string in some
30 encoding, are done by other Tcl commands (respectively string range,
31 string length and encoding convertfrom in the example cases). A binary
32 string in Tcl is merely one where all the characters it contains are in
33 the range \u0000-\u00FF.
34
36 When encoding binary data as a readable string, the starting binary │
37 data is passed to the binary encode command, together with the name of │
38 the encoding to use and any encoding-specific options desired. Data │
39 which has been encoded can be converted back to binary form using │
40 binary decode. The following formats and options are supported. │
41 base64 │
43 The base64 binary encoding is commonly used in mail messages and │
44 XML documents, and uses mostly upper and lower case letters and │
45 digits. It has the distinction of being able to be rewrapped │
46 arbitrarily without losing information. │
47 During encoding, the following options are supported: │
49 -maxlen length │
51 Indicates that the output should be split into lines of │
52 no more than length characters. By default, lines are not │
53 split. │
54 -wrapchar character │
56 Indicates that, when lines are split because of the │
57 -maxlen option, character should be used to separate │
58 lines. By default, this is a newline character, “\n”. │
59 During decoding, the following options are supported: │
61 -strict │
63 Instructs the decoder to throw an error if it encounters │
64 whitespace characters. Otherwise it ignores them. │
65 hex │
67 The hex binary encoding converts each byte to a pair of hexadec‐ │
68 imal digits in big-endian form. │
69 No options are supported during encoding. During decoding, the │
71 following options are supported: │
72 -strict │
74 Instructs the decoder to throw an error if it encounters │
75 whitespace characters. Otherwise it ignores them. │
76 uuencode │
78 The uuencode binary encoding used to be common for transfer of │
79 data between Unix systems and on USENET, but is less common │
80 these days, having been largely superseded by the base64 binary │
81 encoding. │
82 During encoding, the following options are supported (though │
84 changing them may produce files that other implementations of │
85 decoders cannot process): │
86 -maxlen length │
88 Indicates that the output should be split into lines of │
89 no more than length characters. By default, lines are │
90 split every 61 characters, and this must be in the range │
91 3 to 85 due to limitations in the encoding. │
92 -wrapchar character │
94 Indicates that, when lines are split because of the │
95 -maxlen option, character should be used to separate │
96 lines. By default, this is a newline character, “\n”. │
97 During decoding, the following options are supported: │
99 -strict │
101 Instructs the decoder to throw an error if it encounters │
102 unexpected whitespace characters. Otherwise it ignores │
103 them. │
104 Note that neither the encoder nor the decoder handle the header │
106 and footer of the uuencode format. │
107
109 The binary format command generates a binary string whose layout is
110 specified by the formatString and whose contents come from the addi‐
111 tional arguments. The resulting binary value is returned.
112 The formatString consists of a sequence of zero or more field speci‐
114 fiers separated by zero or more spaces. Each field specifier is a sin‐
115 gle type character followed by an optional flag character followed by
116 an optional numeric count. Most field specifiers consume one argument
117 to obtain the value to be formatted. The type character specifies how
118 the value is to be formatted. The count typically indicates how many
119 items of the specified type are taken from the value. If present, the
120 count is a non-negative decimal integer or *, which normally indicates
121 that all of the items in the value are to be used. If the number of
122 arguments does not match the number of fields in the format string that
123 consume arguments, then an error is generated. The flag character is
124 ignored for binary format.
125 Here is a small example to clarify the relation between the field spec‐
127 ifiers and the arguments:
128 binary format d3d {1.0 2.0 3.0 4.0} 0.1
129 The first argument is a list of four numbers, but because of the count
131 of 3 for the associated field specifier, only the first three will be
132 used. The second argument is associated with the second field speci‐
133 fier. The resulting binary string contains the four numbers 1.0, 2.0,
134 3.0 and 0.1.
135 Each type-count pair moves an imaginary cursor through the binary data,
137 storing bytes at the current position and advancing the cursor to just
138 after the last byte stored. The cursor is initially at position 0 at
139 the beginning of the data. The type may be any one of the following
140 characters:
141 a Stores a byte string of length count in the output string. Every
143 character is taken as modulo 256 (i.e. the low byte of every char‐
144 acter is used, and the high byte discarded) so when storing char‐
145 acter strings not wholly expressible using the characters
146 \u0000-\u00ff, the encoding convertto command should be used first
147 to change the string into an external representation if this trun‐
148 cation is not desired (i.e. if the characters are not part of the
149 ISO 8859-1 character set.) If arg has fewer than count bytes,
150 then additional zero bytes are used to pad out the field. If arg
151 is longer than the specified length, the extra characters will be
152 ignored. If count is *, then all of the bytes in arg will be for‐
153 matted. If count is omitted, then one character will be format‐
154 ted. For example,
155 binary format a7a*a alpha bravo charlie
156 will return a string equivalent to alpha\000\000bravoc,
157 binary format a* [encoding convertto utf-8 \u20ac]
158 will return a string equivalent to \342\202\254 (which is the
159 UTF-8 byte sequence for a Euro-currency character) and
160 binary format a* [encoding convertto iso8859-15 \u20ac]
161 will return a string equivalent to \244 (which is the ISO 8859-15
162 byte sequence for a Euro-currency character). Contrast these last
163 two with:
164 binary format a* \u20ac
165 which returns a string equivalent to \254 (i.e. \xac) by truncat‐
166 ing the high-bits of the character, and which is probably not what
167 is desired.
168 A This form is the same as a except that spaces are used for padding
170 instead of nulls. For example,
171 binary format A6A*A alpha bravo charlie
172 will return alpha bravoc.
173 b Stores a string of count binary digits in low-to-high order within
175 each byte in the output string. Arg must contain a sequence of 1
176 and 0 characters. The resulting bytes are emitted in first to
177 last order with the bits being formatted in low-to-high order
178 within each byte. If arg has fewer than count digits, then zeros
179 will be used for the remaining bits. If arg has more than the
180 specified number of digits, the extra digits will be ignored. If
181 count is *, then all of the digits in arg will be formatted. If
182 count is omitted, then one digit will be formatted. If the number
183 of bits formatted does not end at a byte boundary, the remaining
184 bits of the last byte will be zeros. For example,
185 binary format b5b* 11100 111000011010
186 will return a string equivalent to \x07\x87\x05.
187 B This form is the same as b except that the bits are stored in
189 high-to-low order within each byte. For example,
190 binary format B5B* 11100 111000011010
191 will return a string equivalent to \xe0\xe1\xa0.
192 H Stores a string of count hexadecimal digits in high-to-low within
194 each byte in the output string. Arg must contain a sequence of
195 characters in the set “0123456789abcdefABCDEF”. The resulting
196 bytes are emitted in first to last order with the hex digits being
197 formatted in high-to-low order within each byte. If arg has fewer
198 than count digits, then zeros will be used for the remaining dig‐
199 its. If arg has more than the specified number of digits, the
200 extra digits will be ignored. If count is *, then all of the dig‐
201 its in arg will be formatted. If count is omitted, then one digit
202 will be formatted. If the number of digits formatted does not end
203 at a byte boundary, the remaining bits of the last byte will be
204 zeros. For example,
205 binary format H3H*H2 ab DEF 987
206 will return a string equivalent to \xab\x00\xde\xf0\x98.
207 h This form is the same as H except that the digits are stored in
209 low-to-high order within each byte. This is seldom required. For
210 example,
211 binary format h3h*h2 AB def 987
212 will return a string equivalent to \xba\x00\xed\x0f\x89.
213 c Stores one or more 8-bit integer values in the output string. If
215 no count is specified, then arg must consist of an integer value.
216 If count is specified, arg must consist of a list containing at
217 least that many integers. The low-order 8 bits of each integer are
218 stored as a one-byte value at the cursor position. If count is *,
219 then all of the integers in the list are formatted. If the number
220 of elements in the list is greater than count, then the extra ele‐
221 ments are ignored. For example,
222 binary format c3cc* {3 -3 128 1} 260 {2 5}
223 will return a string equivalent to \x03\xfd\x80\x04\x02\x05,
224 whereas
225 binary format c {2 5}
226 will generate an error.
227 s This form is the same as c except that it stores one or more
229 16-bit integers in little-endian byte order in the output string.
230 The low-order 16-bits of each integer are stored as a two-byte
231 value at the cursor position with the least significant byte
232 stored first. For example,
233 binary format s3 {3 -3 258 1}
234 will return a string equivalent to \x03\x00\xfd\xff\x02\x01.
235 S This form is the same as s except that it stores one or more
237 16-bit integers in big-endian byte order in the output string.
238 For example,
239 binary format S3 {3 -3 258 1}
240 will return a string equivalent to \x00\x03\xff\xfd\x01\x02.
241 t This form (mnemonically tiny) is the same as s and S except that
243 it stores the 16-bit integers in the output string in the native
244 byte order of the machine where the Tcl script is running. To
245 determine what the native byte order of the machine is, refer to
246 the byteOrder element of the tcl_platform array.
247 i This form is the same as c except that it stores one or more
249 32-bit integers in little-endian byte order in the output string.
250 The low-order 32-bits of each integer are stored as a four-byte
251 value at the cursor position with the least significant byte
252 stored first. For example,
253 binary format i3 {3 -3 65536 1}
254 will return a string equivalent to
255 \x03\x00\x00\x00\xfd\xff\xff\xff\x00\x00\x01\x00
256 I This form is the same as i except that it stores one or more one
258 or more 32-bit integers in big-endian byte order in the output
259 string. For example,
260 binary format I3 {3 -3 65536 1}
261 will return a string equivalent to
262 \x00\x00\x00\x03\xff\xff\xff\xfd\x00\x01\x00\x00
263 n This form (mnemonically number or normal) is the same as i and I
265 except that it stores the 32-bit integers in the output string in
266 the native byte order of the machine where the Tcl script is run‐
267 ning. To determine what the native byte order of the machine is,
268 refer to the byteOrder element of the tcl_platform array.
269 w This form is the same as c except that it stores one or more
271 64-bit integers in little-endian byte order in the output string.
272 The low-order 64-bits of each integer are stored as an eight-byte
273 value at the cursor position with the least significant byte
274 stored first. For example,
275 binary format w 7810179016327718216
276 will return the string HelloTcl
277 W This form is the same as w except that it stores one or more one
279 or more 64-bit integers in big-endian byte order in the output
280 string. For example,
281 binary format Wc 4785469626960341345 110
282 will return the string BigEndian
283 m This form (mnemonically the mirror of w) is the same as w and W
285 except that it stores the 64-bit integers in the output string in
286 the native byte order of the machine where the Tcl script is run‐
287 ning. To determine what the native byte order of the machine is,
288 refer to the byteOrder element of the tcl_platform array.
289 f This form is the same as c except that it stores one or more one
291 or more single-precision floating point numbers in the machine's
292 native representation in the output string. This representation
293 is not portable across architectures, so it should not be used to
294 communicate floating point numbers across the network. The size
295 of a floating point number may vary across architectures, so the
296 number of bytes that are generated may vary. If the value over‐
297 flows the machine's native representation, then the value of
298 FLT_MAX as defined by the system will be used instead. Because
299 Tcl uses double-precision floating point numbers internally, there
300 may be some loss of precision in the conversion to single-preci‐
301 sion. For example, on a Windows system running on an Intel Pen‐
302 tium processor,
303 binary format f2 {1.6 3.4}
304 will return a string equivalent to
305 \xcd\xcc\xcc\x3f\x9a\x99\x59\x40.
306 r This form (mnemonically real) is the same as f except that it
308 stores the single-precision floating point numbers in little-
309 endian order. This conversion only produces meaningful output
310 when used on machines which use the IEEE floating point represen‐
311 tation (very common, but not universal.)
312 R This form is the same as r except that it stores the single-preci‐
314 sion floating point numbers in big-endian order.
315 d This form is the same as f except that it stores one or more one
317 or more double-precision floating point numbers in the machine's
318 native representation in the output string. For example, on a
319 Windows system running on an Intel Pentium processor,
320 binary format d1 {1.6}
321 will return a string equivalent to
322 \x9a\x99\x99\x99\x99\x99\xf9\x3f.
323 q This form (mnemonically the mirror of d) is the same as d except
325 that it stores the double-precision floating point numbers in lit‐
326 tle-endian order. This conversion only produces meaningful output
327 when used on machines which use the IEEE floating point represen‐
328 tation (very common, but not universal.)
329 Q This form is the same as q except that it stores the double-preci‐
331 sion floating point numbers in big-endian order.
332 x Stores count null bytes in the output string. If count is not
334 specified, stores one null byte. If count is *, generates an
335 error. This type does not consume an argument. For example,
336 binary format a3xa3x2a3 abc def ghi
337 will return a string equivalent to abc\000def\000\000ghi.
338 X Moves the cursor back count bytes in the output string. If count
340 is * or is larger than the current cursor position, then the cur‐
341 sor is positioned at location 0 so that the next byte stored will
342 be the first byte in the result string. If count is omitted then
343 the cursor is moved back one byte. This type does not consume an
344 argument. For example,
345 binary format a3X*a3X2a3 abc def ghi
346 will return dghi.
347 @ Moves the cursor to the absolute location in the output string
349 specified by count. Position 0 refers to the first byte in the
350 output string. If count refers to a position beyond the last byte
351 stored so far, then null bytes will be placed in the uninitialized
352 locations and the cursor will be placed at the specified location.
353 If count is *, then the cursor is moved to the current end of the
354 output string. If count is omitted, then an error will be gener‐
355 ated. This type does not consume an argument. For example,
356 binary format a5@2a1@*a3@10a1 abcde f ghi j
357 will return abfdeghi\000\000j.
358
360 The binary scan command parses fields from a binary string, returning
361 the number of conversions performed. String gives the input bytes to
362 be parsed (one byte per character, and characters not representable as
363 a byte have their high bits chopped) and formatString indicates how to
364 parse it. Each varName gives the name of a variable; when a field is
365 scanned from string the result is assigned to the corresponding vari‐
366 able.
367 As with binary format, the formatString consists of a sequence of zero
369 or more field specifiers separated by zero or more spaces. Each field
370 specifier is a single type character followed by an optional flag char‐
371 acter followed by an optional numeric count. Most field specifiers
372 consume one argument to obtain the variable into which the scanned val‐
373 ues should be placed. The type character specifies how the binary data
374 is to be interpreted. The count typically indicates how many items of
375 the specified type are taken from the data. If present, the count is a
376 non-negative decimal integer or *, which normally indicates that all of
377 the remaining items in the data are to be used. If there are not
378 enough bytes left after the current cursor position to satisfy the cur‐
379 rent field specifier, then the corresponding variable is left untouched
380 and binary scan returns immediately with the number of variables that
381 were set. If there are not enough arguments for all of the fields in
382 the format string that consume arguments, then an error is generated.
383 The flag character “u” may be given to cause some types to be read as
384 unsigned values. The flag is accepted for all field types but is
385 ignored for non-integer fields.
386 A similar example as with binary format should explain the relation
388 between field specifiers and arguments in case of the binary scan sub‐
389 command:
390 binary scan $bytes s3s first second
391 This command (provided the binary string in the variable bytes is long
393 enough) assigns a list of three integers to the variable first and
394 assigns a single value to the variable second. If bytes contains fewer
395 than 8 bytes (i.e. four 2-byte integers), no assignment to second will
396 be made, and if bytes contains fewer than 6 bytes (i.e. three 2-byte
397 integers), no assignment to first will be made. Hence:
398 puts [binary scan abcdefg s3s first second]
399 puts $first
400 puts $second
401 will print (assuming neither variable is set previously):
402 1
403 25185 25699 26213
404 can't read "second": no such variable
405 It is important to note that the c, s, and S (and i and I on 64bit sys‐
407 tems) will be scanned into long data size values. In doing this, val‐
408 ues that have their high bit set (0x80 for chars, 0x8000 for shorts,
409 0x80000000 for ints), will be sign extended. Thus the following will
410 occur:
411 set signShort [binary format s1 0x8000]
412 binary scan $signShort s1 val; # val == 0xFFFF8000
413 If you require unsigned values you can include the “u” flag character
414 following the field type. For example, to read an unsigned short value:
415 set signShort [binary format s1 0x8000]
416 binary scan $signShort su1 val; # val == 0x00008000
417 Each type-count pair moves an imaginary cursor through the binary data,
419 reading bytes from the current position. The cursor is initially at
420 position 0 at the beginning of the data. The type may be any one of
421 the following characters:
422 a The data is a byte string of length count. If count is *, then
424 all of the remaining bytes in string will be scanned into the
425 variable. If count is omitted, then one byte will be scanned.
426 All bytes scanned will be interpreted as being characters in the
427 range \u0000-\u00ff so the encoding convertfrom command will be
428 needed if the string is not a binary string or a string encoded in
429 ISO 8859-1. For example,
430 binary scan abcde\000fghi a6a10 var1 var2
431 will return 1 with the string equivalent to abcde\000 stored in
432 var1 and var2 left unmodified, and
433 binary scan \342\202\254 a* var1
434 set var2 [encoding convertfrom utf-8 $var1]
435 will store a Euro-currency character in var2.
436 A This form is the same as a, except trailing blanks and nulls are
438 stripped from the scanned value before it is stored in the vari‐
439 able. For example,
440 binary scan "abc efghi \000" A* var1
441 will return 1 with abc efghi stored in var1.
442 b The data is turned into a string of count binary digits in low-to-
444 high order represented as a sequence of “1” and “0” characters.
445 The data bytes are scanned in first to last order with the bits
446 being taken in low-to-high order within each byte. Any extra bits
447 in the last byte are ignored. If count is *, then all of the
448 remaining bits in string will be scanned. If count is omitted,
449 then one bit will be scanned. For example,
450 binary scan \x07\x87\x05 b5b* var1 var2
451 will return 2 with 11100 stored in var1 and 1110000110100000
452 stored in var2.
453 B This form is the same as b, except the bits are taken in high-to-
455 low order within each byte. For example,
456 binary scan \x70\x87\x05 B5B* var1 var2
457 will return 2 with 01110 stored in var1 and 1000011100000101
458 stored in var2.
459 H The data is turned into a string of count hexadecimal digits in
461 high-to-low order represented as a sequence of characters in the
462 set “0123456789abcdef”. The data bytes are scanned in first to
463 last order with the hex digits being taken in high-to-low order
464 within each byte. Any extra bits in the last byte are ignored. If
465 count is *, then all of the remaining hex digits in string will be
466 scanned. If count is omitted, then one hex digit will be scanned.
467 For example,
468 binary scan \x07\xC6\x05\x1f\x34 H3H* var1 var2
469 will return 2 with 07c stored in var1 and 051f34 stored in var2.
470 h This form is the same as H, except the digits are taken in reverse
472 (low-to-high) order within each byte. For example,
473 binary scan \x07\x86\x05\x12\x34 h3h* var1 var2
474 will return 2 with 706 stored in var1 and 502143 stored in var2.
475 Note that most code that wishes to parse the hexadecimal digits
477 from multiple bytes in order should use the H format.
478 c The data is turned into count 8-bit signed integers and stored in
480 the corresponding variable as a list. If count is *, then all of
481 the remaining bytes in string will be scanned. If count is omit‐
482 ted, then one 8-bit integer will be scanned. For example,
483 binary scan \x07\x86\x05 c2c* var1 var2
484 will return 2 with 7 -122 stored in var1 and 5 stored in var2.
485 Note that the integers returned are signed, but they can be con‐
486 verted to unsigned 8-bit quantities using an expression like:
487 set num [expr { $num & 0xff }]
488 s The data is interpreted as count 16-bit signed integers repre‐
490 sented in little-endian byte order. The integers are stored in
491 the corresponding variable as a list. If count is *, then all of
492 the remaining bytes in string will be scanned. If count is omit‐
493 ted, then one 16-bit integer will be scanned. For example,
494 binary scan \x05\x00\x07\x00\xf0\xff s2s* var1 var2
495 will return 2 with 5 7 stored in var1 and -16 stored in var2.
496 Note that the integers returned are signed, but they can be con‐
497 verted to unsigned 16-bit quantities using an expression like:
498 set num [expr { $num & 0xffff }]
499 S This form is the same as s except that the data is interpreted as
501 count 16-bit signed integers represented in big-endian byte order.
502 For example,
503 binary scan \x00\x05\x00\x07\xff\xf0 S2S* var1 var2
504 will return 2 with 5 7 stored in var1 and -16 stored in var2.
505 t The data is interpreted as count 16-bit signed integers repre‐
507 sented in the native byte order of the machine running the Tcl
508 script. It is otherwise identical to s and S. To determine what
509 the native byte order of the machine is, refer to the byteOrder
510 element of the tcl_platform array.
511 i The data is interpreted as count 32-bit signed integers repre‐
513 sented in little-endian byte order. The integers are stored in
514 the corresponding variable as a list. If count is *, then all of
515 the remaining bytes in string will be scanned. If count is omit‐
516 ted, then one 32-bit integer will be scanned. For example,
517 set str \x05\x00\x00\x00\x07\x00\x00\x00\xf0\xff\xff\xff
518 binary scan $str i2i* var1 var2
519 will return 2 with 5 7 stored in var1 and -16 stored in var2.
520 Note that the integers returned are signed, but they can be con‐
521 verted to unsigned 32-bit quantities using an expression like:
522 set num [expr { $num & 0xffffffff }]
523 I This form is the same as I except that the data is interpreted as
525 count 32-bit signed integers represented in big-endian byte order.
526 For example,
527 set str \x00\x00\x00\x05\x00\x00\x00\x07\xff\xff\xff\xf0
528 binary scan $str I2I* var1 var2
529 will return 2 with 5 7 stored in var1 and -16 stored in var2.
530 n The data is interpreted as count 32-bit signed integers repre‐
532 sented in the native byte order of the machine running the Tcl
533 script. It is otherwise identical to i and I. To determine what
534 the native byte order of the machine is, refer to the byteOrder
535 element of the tcl_platform array.
536 w The data is interpreted as count 64-bit signed integers repre‐
538 sented in little-endian byte order. The integers are stored in
539 the corresponding variable as a list. If count is *, then all of
540 the remaining bytes in string will be scanned. If count is omit‐
541 ted, then one 64-bit integer will be scanned. For example,
542 set str \x05\x00\x00\x00\x07\x00\x00\x00\xf0\xff\xff\xff
543 binary scan $str wi* var1 var2
544 will return 2 with 30064771077 stored in var1 and -16 stored in
545 var2. Note that the integers returned are signed and cannot be
546 represented by Tcl as unsigned values.
547 W This form is the same as w except that the data is interpreted as
549 count 64-bit signed integers represented in big-endian byte order.
550 For example,
551 set str \x00\x00\x00\x05\x00\x00\x00\x07\xff\xff\xff\xf0
552 binary scan $str WI* var1 var2
553 will return 2 with 21474836487 stored in var1 and -16 stored in
554 var2.
555 m The data is interpreted as count 64-bit signed integers repre‐
557 sented in the native byte order of the machine running the Tcl
558 script. It is otherwise identical to w and W. To determine what
559 the native byte order of the machine is, refer to the byteOrder
560 element of the tcl_platform array.
561 f The data is interpreted as count single-precision floating point
563 numbers in the machine's native representation. The floating
564 point numbers are stored in the corresponding variable as a list.
565 If count is *, then all of the remaining bytes in string will be
566 scanned. If count is omitted, then one single-precision floating
567 point number will be scanned. The size of a floating point number
568 may vary across architectures, so the number of bytes that are
569 scanned may vary. If the data does not represent a valid floating
570 point number, the resulting value is undefined and compiler depen‐
571 dent. For example, on a Windows system running on an Intel Pen‐
572 tium processor,
573 binary scan \x3f\xcc\xcc\xcd f var1
574 will return 1 with 1.6000000238418579 stored in var1.
575 r This form is the same as f except that the data is interpreted as
577 count single-precision floating point number in little-endian
578 order. This conversion is not portable to the minority of systems
579 not using IEEE floating point representations.
580 R This form is the same as f except that the data is interpreted as
582 count single-precision floating point number in big-endian order.
583 This conversion is not portable to the minority of systems not
584 using IEEE floating point representations.
585 d This form is the same as f except that the data is interpreted as
587 count double-precision floating point numbers in the machine's
588 native representation. For example, on a Windows system running on
589 an Intel Pentium processor,
590 binary scan \x9a\x99\x99\x99\x99\x99\xf9\x3f d var1
591 will return 1 with 1.6000000000000001 stored in var1.
592 q This form is the same as d except that the data is interpreted as
594 count double-precision floating point number in little-endian
595 order. This conversion is not portable to the minority of systems
596 not using IEEE floating point representations.
597 Q This form is the same as d except that the data is interpreted as
599 count double-precision floating point number in big-endian order.
600 This conversion is not portable to the minority of systems not
601 using IEEE floating point representations.
602 x Moves the cursor forward count bytes in string. If count is * or
604 is larger than the number of bytes after the current cursor posi‐
605 tion, then the cursor is positioned after the last byte in string.
606 If count is omitted, then the cursor is moved forward one byte.
607 Note that this type does not consume an argument. For example,
608 binary scan \x01\x02\x03\x04 x2H* var1
609 will return 1 with 0304 stored in var1.
610 X Moves the cursor back count bytes in string. If count is * or is
612 larger than the current cursor position, then the cursor is posi‐
613 tioned at location 0 so that the next byte scanned will be the
614 first byte in string. If count is omitted then the cursor is
615 moved back one byte. Note that this type does not consume an
616 argument. For example,
617 binary scan \x01\x02\x03\x04 c2XH* var1 var2
618 will return 2 with 1 2 stored in var1 and 020304 stored in var2.
619 @ Moves the cursor to the absolute location in the data string spec‐
621 ified by count. Note that position 0 refers to the first byte in
622 string. If count refers to a position beyond the end of string,
623 then the cursor is positioned after the last byte. If count is
624 omitted, then an error will be generated. For example,
625 binary scan \x01\x02\x03\x04 c2@1H* var1 var2
626 will return 2 with 1 2 stored in var1 and 020304 stored in var2.
627
629 The r, R, q and Q conversions will only work reliably for transferring
630 data between computers which are all using IEEE floating point repre‐
631 sentations. This is very common, but not universal. To transfer
632 floating-point numbers portably between all architectures, use their
633 textual representation (as produced by format) instead.
634
636 This is a procedure to write a Tcl string to a binary-encoded channel
637 as UTF-8 data preceded by a length word:
638 proc writeString {channel string} {
640 set data [encoding convertto utf-8 $string]
641 puts -nonewline [binary format Ia* \
642 [string length $data] $data]
643 }
644 This procedure reads a string from a channel that was written by the
646 previously presented writeString procedure:
647 proc readString {channel} {
649 if {![binary scan [read $channel 4] I length]} {
650 error "missing length"
651 }
652 set data [read $channel $length]
653 return [encoding convertfrom utf-8 $data]
654 }
655 This converts the contents of a file (named in the variable filename)
657 to base64 and prints them:
658 set f [open $filename rb]
660 set data [read $f]
661 close $f
662 puts [binary encode base64 -maxlen 64 $data]
663
665 encoding(n), format(n), scan(n), string(n), tcl_platform(n)
666
668 binary, format, scan
669Tcl 8.0 binary(n)