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 en‐
30 coding, 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 bi‐ │
40 nary 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 ar‐ │
46 bitrarily 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 any characters that are not strictly part of the encoding │
65 itself. Otherwise it ignores them. RFC 2045 calls for │
66 base64 decoders to be non-strict. │
67 hex │
69 The hex binary encoding converts each byte to a pair of hexadec‐ │
70 imal digits in big-endian form. │
71 No options are supported during encoding. During decoding, the │
73 following options are supported: │
74 -strict │
76 Instructs the decoder to throw an error if it encounters │
77 whitespace characters. Otherwise it ignores them. │
78 uuencode │
80 The uuencode binary encoding used to be common for transfer of │
81 data between Unix systems and on USENET, but is less common │
82 these days, having been largely superseded by the base64 binary │
83 encoding. │
84 During encoding, the following options are supported (though │
86 changing them may produce files that other implementations of │
87 decoders cannot process): │
88 -maxlen length │
90 Indicates the maximum number of characters to produce for │
91 each encoded line. The valid range is 5 to 85. Line │
92 lengths outside that range cannot be accommodated by the │
93 encoding format. The default value is 61. │
94 -wrapchar character │
96 Indicates the character(s) to use to mark the end of each │
97 encoded line. Acceptable values are a sequence of zero │
98 or more characters from the set { \x09 (TAB), \x0B (VT), │
99 \x0C (FF), \x0D (CR) } followed by zero or one newline │
100 \x0A (LF). Any other values are rejected because they │
101 would generate encoded text that could not be decoded. │
102 The default value is a single newline. │
103 During decoding, the following options are supported: │
105 -strict │
107 Instructs the decoder to throw an error if it encounters │
108 anything outside of the standard encoding format. Without │
109 this option, the decoder tolerates some deviations, │
110 mostly to forgive reflows of lines between the encoder │
111 and decoder. │
112 Note that neither the encoder nor the decoder handle the header │
114 and footer of the uuencode format. │
115
117 The binary format command generates a binary string whose layout is
118 specified by the formatString and whose contents come from the addi‐
119 tional arguments. The resulting binary value is returned.
120 The formatString consists of a sequence of zero or more field speci‐
122 fiers separated by zero or more spaces. Each field specifier is a sin‐
123 gle type character followed by an optional flag character followed by
124 an optional numeric count. Most field specifiers consume one argument
125 to obtain the value to be formatted. The type character specifies how
126 the value is to be formatted. The count typically indicates how many
127 items of the specified type are taken from the value. If present, the
128 count is a non-negative decimal integer or *, which normally indicates
129 that all of the items in the value are to be used. If the number of
130 arguments does not match the number of fields in the format string that
131 consume arguments, then an error is generated. The flag character is
132 ignored for binary format.
133 Here is a small example to clarify the relation between the field spec‐
135 ifiers and the arguments:
136 binary format d3d {1.0 2.0 3.0 4.0} 0.1
137 The first argument is a list of four numbers, but because of the count
139 of 3 for the associated field specifier, only the first three will be
140 used. The second argument is associated with the second field speci‐
141 fier. The resulting binary string contains the four numbers 1.0, 2.0,
142 3.0 and 0.1.
143 Each type-count pair moves an imaginary cursor through the binary data,
145 storing bytes at the current position and advancing the cursor to just
146 after the last byte stored. The cursor is initially at position 0 at
147 the beginning of the data. The type may be any one of the following
148 characters:
149 a Stores a byte string of length count in the output string. Every
151 character is taken as modulo 256 (i.e. the low byte of every char‐
152 acter is used, and the high byte discarded) so when storing char‐
153 acter strings not wholly expressible using the characters
154 \u0000-\u00ff, the encoding convertto command should be used first
155 to change the string into an external representation if this trun‐
156 cation is not desired (i.e. if the characters are not part of the
157 ISO 8859-1 character set.) If arg has fewer than count bytes,
158 then additional zero bytes are used to pad out the field. If arg
159 is longer than the specified length, the extra characters will be
160 ignored. If count is *, then all of the bytes in arg will be for‐
161 matted. If count is omitted, then one character will be format‐
162 ted. For example,
163 binary format a7a*a alpha bravo charlie
164 will return a string equivalent to alpha\000\000bravoc,
165 binary format a* [encoding convertto utf-8 \u20ac]
166 will return a string equivalent to \342\202\254 (which is the
167 UTF-8 byte sequence for a Euro-currency character) and
168 binary format a* [encoding convertto iso8859-15 \u20ac]
169 will return a string equivalent to \244 (which is the ISO 8859-15
170 byte sequence for a Euro-currency character). Contrast these last
171 two with:
172 binary format a* \u20ac
173 which returns a string equivalent to \254 (i.e. \xac) by truncat‐
174 ing the high-bits of the character, and which is probably not what
175 is desired.
176 A This form is the same as a except that spaces are used for padding
178 instead of nulls. For example,
179 binary format A6A*A alpha bravo charlie
180 will return alpha bravoc.
181 b Stores a string of count binary digits in low-to-high order within
183 each byte in the output string. Arg must contain a sequence of 1
184 and 0 characters. The resulting bytes are emitted in first to
185 last order with the bits being formatted in low-to-high order
186 within each byte. If arg has fewer than count digits, then zeros
187 will be used for the remaining bits. If arg has more than the
188 specified number of digits, the extra digits will be ignored. If
189 count is *, then all of the digits in arg will be formatted. If
190 count is omitted, then one digit will be formatted. If the number
191 of bits formatted does not end at a byte boundary, the remaining
192 bits of the last byte will be zeros. For example,
193 binary format b5b* 11100 111000011010
194 will return a string equivalent to \x07\x87\x05.
195 B This form is the same as b except that the bits are stored in
197 high-to-low order within each byte. For example,
198 binary format B5B* 11100 111000011010
199 will return a string equivalent to \xe0\xe1\xa0.
200 H Stores a string of count hexadecimal digits in high-to-low within
202 each byte in the output string. Arg must contain a sequence of
203 characters in the set “0123456789abcdefABCDEF”. The resulting
204 bytes are emitted in first to last order with the hex digits being
205 formatted in high-to-low order within each byte. If arg has fewer
206 than count digits, then zeros will be used for the remaining dig‐
207 its. If arg has more than the specified number of digits, the ex‐
208 tra digits will be ignored. If count is *, then all of the digits
209 in arg will be formatted. If count is omitted, then one digit
210 will be formatted. If the number of digits formatted does not end
211 at a byte boundary, the remaining bits of the last byte will be
212 zeros. For example,
213 binary format H3H*H2 ab DEF 987
214 will return a string equivalent to \xab\x00\xde\xf0\x98.
215 h This form is the same as H except that the digits are stored in
217 low-to-high order within each byte. This is seldom required. For
218 example,
219 binary format h3h*h2 AB def 987
220 will return a string equivalent to \xba\x00\xed\x0f\x89.
221 c Stores one or more 8-bit integer values in the output string. If
223 no count is specified, then arg must consist of an integer value.
224 If count is specified, arg must consist of a list containing at
225 least that many integers. The low-order 8 bits of each integer are
226 stored as a one-byte value at the cursor position. If count is *,
227 then all of the integers in the list are formatted. If the number
228 of elements in the list is greater than count, then the extra ele‐
229 ments are ignored. For example,
230 binary format c3cc* {3 -3 128 1} 260 {2 5}
231 will return a string equivalent to \x03\xfd\x80\x04\x02\x05,
232 whereas
233 binary format c {2 5}
234 will generate an error.
235 s This form is the same as c except that it stores one or more
237 16-bit integers in little-endian byte order in the output string.
238 The low-order 16-bits of each integer are stored as a two-byte
239 value at the cursor position with the least significant byte
240 stored first. For example,
241 binary format s3 {3 -3 258 1}
242 will return a string equivalent to \x03\x00\xfd\xff\x02\x01.
243 S This form is the same as s except that it stores one or more
245 16-bit integers in big-endian byte order in the output string.
246 For example,
247 binary format S3 {3 -3 258 1}
248 will return a string equivalent to \x00\x03\xff\xfd\x01\x02.
249 t This form (mnemonically tiny) is the same as s and S except that
251 it stores the 16-bit integers in the output string in the native
252 byte order of the machine where the Tcl script is running. To de‐
253 termine what the native byte order of the machine is, refer to the
254 byteOrder element of the tcl_platform array.
255 i This form is the same as c except that it stores one or more
257 32-bit integers in little-endian byte order in the output string.
258 The low-order 32-bits of each integer are stored as a four-byte
259 value at the cursor position with the least significant byte
260 stored first. For example,
261 binary format i3 {3 -3 65536 1}
262 will return a string equivalent to
263 \x03\x00\x00\x00\xfd\xff\xff\xff\x00\x00\x01\x00
264 I This form is the same as i except that it stores one or more one
266 or more 32-bit integers in big-endian byte order in the output
267 string. For example,
268 binary format I3 {3 -3 65536 1}
269 will return a string equivalent to
270 \x00\x00\x00\x03\xff\xff\xff\xfd\x00\x01\x00\x00
271 n This form (mnemonically number or normal) is the same as i and I
273 except that it stores the 32-bit integers in the output string in
274 the native byte order of the machine where the Tcl script is run‐
275 ning. To determine what the native byte order of the machine is,
276 refer to the byteOrder element of the tcl_platform array.
277 w This form is the same as c except that it stores one or more
279 64-bit integers in little-endian byte order in the output string.
280 The low-order 64-bits of each integer are stored as an eight-byte
281 value at the cursor position with the least significant byte
282 stored first. For example,
283 binary format w 7810179016327718216
284 will return the string HelloTcl
285 W This form is the same as w except that it stores one or more one
287 or more 64-bit integers in big-endian byte order in the output
288 string. For example,
289 binary format Wc 4785469626960341345 110
290 will return the string BigEndian
291 m This form (mnemonically the mirror of w) is the same as w and W
293 except that it stores the 64-bit integers in the output string in
294 the native byte order of the machine where the Tcl script is run‐
295 ning. To determine what the native byte order of the machine is,
296 refer to the byteOrder element of the tcl_platform array.
297 f This form is the same as c except that it stores one or more one
299 or more single-precision floating point numbers in the machine's
300 native representation in the output string. This representation
301 is not portable across architectures, so it should not be used to
302 communicate floating point numbers across the network. The size
303 of a floating point number may vary across architectures, so the
304 number of bytes that are generated may vary. If the value over‐
305 flows the machine's native representation, then the value of
306 FLT_MAX as defined by the system will be used instead. Because
307 Tcl uses double-precision floating point numbers internally, there
308 may be some loss of precision in the conversion to single-preci‐
309 sion. For example, on a Windows system running on an Intel Pen‐
310 tium processor,
311 binary format f2 {1.6 3.4}
312 will return a string equivalent to
313 \xcd\xcc\xcc\x3f\x9a\x99\x59\x40.
314 r This form (mnemonically real) is the same as f except that it
316 stores the single-precision floating point numbers in little-en‐
317 dian order. This conversion only produces meaningful output when
318 used on machines which use the IEEE floating point representation
319 (very common, but not universal.)
320 R This form is the same as r except that it stores the single-preci‐
322 sion floating point numbers in big-endian order.
323 d This form is the same as f except that it stores one or more one
325 or more double-precision floating point numbers in the machine's
326 native representation in the output string. For example, on a
327 Windows system running on an Intel Pentium processor,
328 binary format d1 {1.6}
329 will return a string equivalent to
330 \x9a\x99\x99\x99\x99\x99\xf9\x3f.
331 q This form (mnemonically the mirror of d) is the same as d except
333 that it stores the double-precision floating point numbers in lit‐
334 tle-endian order. This conversion only produces meaningful output
335 when used on machines which use the IEEE floating point represen‐
336 tation (very common, but not universal.)
337 Q This form is the same as q except that it stores the double-preci‐
339 sion floating point numbers in big-endian order.
340 x Stores count null bytes in the output string. If count is not
342 specified, stores one null byte. If count is *, generates an er‐
343 ror. This type does not consume an argument. For example,
344 binary format a3xa3x2a3 abc def ghi
345 will return a string equivalent to abc\000def\000\000ghi.
346 X Moves the cursor back count bytes in the output string. If count
348 is * or is larger than the current cursor position, then the cur‐
349 sor is positioned at location 0 so that the next byte stored will
350 be the first byte in the result string. If count is omitted then
351 the cursor is moved back one byte. This type does not consume an
352 argument. For example,
353 binary format a3X*a3X2a3 abc def ghi
354 will return dghi.
355 @ Moves the cursor to the absolute location in the output string
357 specified by count. Position 0 refers to the first byte in the
358 output string. If count refers to a position beyond the last byte
359 stored so far, then null bytes will be placed in the uninitialized
360 locations and the cursor will be placed at the specified location.
361 If count is *, then the cursor is moved to the current end of the
362 output string. If count is omitted, then an error will be gener‐
363 ated. This type does not consume an argument. For example,
364 binary format a5@2a1@*a3@10a1 abcde f ghi j
365 will return abfdeghi\000\000j.
366
368 The binary scan command parses fields from a binary string, returning
369 the number of conversions performed. String gives the input bytes to
370 be parsed (one byte per character, and characters not representable as
371 a byte have their high bits chopped) and formatString indicates how to
372 parse it. Each varName gives the name of a variable; when a field is
373 scanned from string the result is assigned to the corresponding vari‐
374 able.
375 As with binary format, the formatString consists of a sequence of zero
377 or more field specifiers separated by zero or more spaces. Each field
378 specifier is a single type character followed by an optional flag char‐
379 acter followed by an optional numeric count. Most field specifiers
380 consume one argument to obtain the variable into which the scanned val‐
381 ues should be placed. The type character specifies how the binary data
382 is to be interpreted. The count typically indicates how many items of
383 the specified type are taken from the data. If present, the count is a
384 non-negative decimal integer or *, which normally indicates that all of
385 the remaining items in the data are to be used. If there are not
386 enough bytes left after the current cursor position to satisfy the cur‐
387 rent field specifier, then the corresponding variable is left untouched
388 and binary scan returns immediately with the number of variables that
389 were set. If there are not enough arguments for all of the fields in
390 the format string that consume arguments, then an error is generated.
391 The flag character “u” may be given to cause some types to be read as
392 unsigned values. The flag is accepted for all field types but is ig‐
393 nored for non-integer fields.
394 A similar example as with binary format should explain the relation be‐
396 tween field specifiers and arguments in case of the binary scan subcom‐
397 mand:
398 binary scan $bytes s3s first second
399 This command (provided the binary string in the variable bytes is long
401 enough) assigns a list of three integers to the variable first and as‐
402 signs a single value to the variable second. If bytes contains fewer
403 than 8 bytes (i.e. four 2-byte integers), no assignment to second will
404 be made, and if bytes contains fewer than 6 bytes (i.e. three 2-byte
405 integers), no assignment to first will be made. Hence:
406 puts [binary scan abcdefg s3s first second]
407 puts $first
408 puts $second
409 will print (assuming neither variable is set previously):
410 1
411 25185 25699 26213
412 can't read "second": no such variable
413 It is important to note that the c, s, and S (and i and I on 64bit sys‐
415 tems) will be scanned into long data size values. In doing this, val‐
416 ues that have their high bit set (0x80 for chars, 0x8000 for shorts,
417 0x80000000 for ints), will be sign extended. Thus the following will
418 occur:
419 set signShort [binary format s1 0x8000]
420 binary scan $signShort s1 val; # val == 0xFFFF8000
421 If you require unsigned values you can include the “u” flag character
422 following the field type. For example, to read an unsigned short value:
423 set signShort [binary format s1 0x8000]
424 binary scan $signShort su1 val; # val == 0x00008000
425 Each type-count pair moves an imaginary cursor through the binary data,
427 reading bytes from the current position. The cursor is initially at
428 position 0 at the beginning of the data. The type may be any one of
429 the following characters:
430 a The data is a byte string of length count. If count is *, then
432 all of the remaining bytes in string will be scanned into the
433 variable. If count is omitted, then one byte will be scanned.
434 All bytes scanned will be interpreted as being characters in the
435 range \u0000-\u00ff so the encoding convertfrom command will be
436 needed if the string is not a binary string or a string encoded in
437 ISO 8859-1. For example,
438 binary scan abcde\000fghi a6a10 var1 var2
439 will return 1 with the string equivalent to abcde\000 stored in
440 var1 and var2 left unmodified, and
441 binary scan \342\202\254 a* var1
442 set var2 [encoding convertfrom utf-8 $var1]
443 will store a Euro-currency character in var2.
444 A This form is the same as a, except trailing blanks and nulls are
446 stripped from the scanned value before it is stored in the vari‐
447 able. For example,
448 binary scan "abc efghi \000" A* var1
449 will return 1 with abc efghi stored in var1.
450 b The data is turned into a string of count binary digits in low-to-
452 high order represented as a sequence of “1” and “0” characters.
453 The data bytes are scanned in first to last order with the bits
454 being taken in low-to-high order within each byte. Any extra bits
455 in the last byte are ignored. If count is *, then all of the re‐
456 maining bits in string will be scanned. If count is omitted, then
457 one bit will be scanned. For example,
458 binary scan \x07\x87\x05 b5b* var1 var2
459 will return 2 with 11100 stored in var1 and 1110000110100000
460 stored in var2.
461 B This form is the same as b, except the bits are taken in high-to-
463 low order within each byte. For example,
464 binary scan \x70\x87\x05 B5B* var1 var2
465 will return 2 with 01110 stored in var1 and 1000011100000101
466 stored in var2.
467 H The data is turned into a string of count hexadecimal digits in
469 high-to-low order represented as a sequence of characters in the
470 set “0123456789abcdef”. The data bytes are scanned in first to
471 last order with the hex digits being taken in high-to-low order
472 within each byte. Any extra bits in the last byte are ignored. If
473 count is *, then all of the remaining hex digits in string will be
474 scanned. If count is omitted, then one hex digit will be scanned.
475 For example,
476 binary scan \x07\xC6\x05\x1f\x34 H3H* var1 var2
477 will return 2 with 07c stored in var1 and 051f34 stored in var2.
478 h This form is the same as H, except the digits are taken in reverse
480 (low-to-high) order within each byte. For example,
481 binary scan \x07\x86\x05\x12\x34 h3h* var1 var2
482 will return 2 with 706 stored in var1 and 502143 stored in var2.
483 Note that most code that wishes to parse the hexadecimal digits
485 from multiple bytes in order should use the H format.
486 c The data is turned into count 8-bit signed integers and stored in
488 the corresponding variable as a list. If count is *, then all of
489 the remaining bytes in string will be scanned. If count is omit‐
490 ted, then one 8-bit integer will be scanned. For example,
491 binary scan \x07\x86\x05 c2c* var1 var2
492 will return 2 with 7 -122 stored in var1 and 5 stored in var2.
493 Note that the integers returned are signed, but they can be con‐
494 verted to unsigned 8-bit quantities using an expression like:
495 set num [expr { $num & 0xFF }]
496 s The data is interpreted as count 16-bit signed integers repre‐
498 sented in little-endian byte order. The integers are stored in
499 the corresponding variable as a list. If count is *, then all of
500 the remaining bytes in string will be scanned. If count is omit‐
501 ted, then one 16-bit integer will be scanned. For example,
502 binary scan \x05\x00\x07\x00\xf0\xff s2s* var1 var2
503 will return 2 with 5 7 stored in var1 and -16 stored in var2.
504 Note that the integers returned are signed, but they can be con‐
505 verted to unsigned 16-bit quantities using an expression like:
506 set num [expr { $num & 0xFFFF }]
507 S This form is the same as s except that the data is interpreted as
509 count 16-bit signed integers represented in big-endian byte order.
510 For example,
511 binary scan \x00\x05\x00\x07\xff\xf0 S2S* var1 var2
512 will return 2 with 5 7 stored in var1 and -16 stored in var2.
513 t The data is interpreted as count 16-bit signed integers repre‐
515 sented in the native byte order of the machine running the Tcl
516 script. It is otherwise identical to s and S. To determine what
517 the native byte order of the machine is, refer to the byteOrder
518 element of the tcl_platform array.
519 i The data is interpreted as count 32-bit signed integers repre‐
521 sented in little-endian byte order. The integers are stored in
522 the corresponding variable as a list. If count is *, then all of
523 the remaining bytes in string will be scanned. If count is omit‐
524 ted, then one 32-bit integer will be scanned. For example,
525 set str \x05\x00\x00\x00\x07\x00\x00\x00\xf0\xff\xff\xff
526 binary scan $str i2i* var1 var2
527 will return 2 with 5 7 stored in var1 and -16 stored in var2.
528 Note that the integers returned are signed, but they can be con‐
529 verted to unsigned 32-bit quantities using an expression like:
530 set num [expr { $num & 0xFFFFFFFF }]
531 I This form is the same as I except that the data is interpreted as
533 count 32-bit signed integers represented in big-endian byte order.
534 For example,
535 set str \x00\x00\x00\x05\x00\x00\x00\x07\xff\xff\xff\xf0
536 binary scan $str I2I* var1 var2
537 will return 2 with 5 7 stored in var1 and -16 stored in var2.
538 n The data is interpreted as count 32-bit signed integers repre‐
540 sented in the native byte order of the machine running the Tcl
541 script. It is otherwise identical to i and I. To determine what
542 the native byte order of the machine is, refer to the byteOrder
543 element of the tcl_platform array.
544 w The data is interpreted as count 64-bit signed integers repre‐
546 sented in little-endian byte order. The integers are stored in
547 the corresponding variable as a list. If count is *, then all of
548 the remaining bytes in string will be scanned. If count is omit‐
549 ted, then one 64-bit integer will be scanned. For example,
550 set str \x05\x00\x00\x00\x07\x00\x00\x00\xf0\xff\xff\xff
551 binary scan $str wi* var1 var2
552 will return 2 with 30064771077 stored in var1 and -16 stored in
553 var2. Note that the integers returned are signed and cannot be
554 represented by Tcl as unsigned values.
555 W This form is the same as w except that the data is interpreted as
557 count 64-bit signed integers represented in big-endian byte order.
558 For example,
559 set str \x00\x00\x00\x05\x00\x00\x00\x07\xff\xff\xff\xf0
560 binary scan $str WI* var1 var2
561 will return 2 with 21474836487 stored in var1 and -16 stored in
562 var2.
563 m The data is interpreted as count 64-bit signed integers repre‐
565 sented in the native byte order of the machine running the Tcl
566 script. It is otherwise identical to w and W. To determine what
567 the native byte order of the machine is, refer to the byteOrder
568 element of the tcl_platform array.
569 f The data is interpreted as count single-precision floating point
571 numbers in the machine's native representation. The floating
572 point numbers are stored in the corresponding variable as a list.
573 If count is *, then all of the remaining bytes in string will be
574 scanned. If count is omitted, then one single-precision floating
575 point number will be scanned. The size of a floating point number
576 may vary across architectures, so the number of bytes that are
577 scanned may vary. If the data does not represent a valid floating
578 point number, the resulting value is undefined and compiler depen‐
579 dent. For example, on a Windows system running on an Intel Pen‐
580 tium processor,
581 binary scan \x3f\xcc\xcc\xcd f var1
582 will return 1 with 1.6000000238418579 stored in var1.
583 r This form is the same as f except that the data is interpreted as
585 count single-precision floating point number in little-endian or‐
586 der. This conversion is not portable to the minority of systems
587 not using IEEE floating point representations.
588 R This form is the same as f except that the data is interpreted as
590 count single-precision floating point number in big-endian order.
591 This conversion is not portable to the minority of systems not us‐
592 ing IEEE floating point representations.
593 d This form is the same as f except that the data is interpreted as
595 count double-precision floating point numbers in the machine's na‐
596 tive representation. For example, on a Windows system running on
597 an Intel Pentium processor,
598 binary scan \x9a\x99\x99\x99\x99\x99\xf9\x3f d var1
599 will return 1 with 1.6000000000000001 stored in var1.
600 q This form is the same as d except that the data is interpreted as
602 count double-precision floating point number in little-endian or‐
603 der. This conversion is not portable to the minority of systems
604 not using IEEE floating point representations.
605 Q This form is the same as d except that the data is interpreted as
607 count double-precision floating point number in big-endian order.
608 This conversion is not portable to the minority of systems not us‐
609 ing IEEE floating point representations.
610 x Moves the cursor forward count bytes in string. If count is * or
612 is larger than the number of bytes after the current cursor posi‐
613 tion, then the cursor is positioned after the last byte in string.
614 If count is omitted, then the cursor is moved forward one byte.
615 Note that this type does not consume an argument. For example,
616 binary scan \x01\x02\x03\x04 x2H* var1
617 will return 1 with 0304 stored in var1.
618 X Moves the cursor back count bytes in string. If count is * or is
620 larger than the current cursor position, then the cursor is posi‐
621 tioned at location 0 so that the next byte scanned will be the
622 first byte in string. If count is omitted then the cursor is
623 moved back one byte. Note that this type does not consume an ar‐
624 gument. For example,
625 binary scan \x01\x02\x03\x04 c2XH* var1 var2
626 will return 2 with 1 2 stored in var1 and 020304 stored in var2.
627 @ Moves the cursor to the absolute location in the data string spec‐
629 ified by count. Note that position 0 refers to the first byte in
630 string. If count refers to a position beyond the end of string,
631 then the cursor is positioned after the last byte. If count is
632 omitted, then an error will be generated. For example,
633 binary scan \x01\x02\x03\x04 c2@1H* var1 var2
634 will return 2 with 1 2 stored in var1 and 020304 stored in var2.
635
637 The r, R, q and Q conversions will only work reliably for transferring
638 data between computers which are all using IEEE floating point repre‐
639 sentations. This is very common, but not universal. To transfer
640 floating-point numbers portably between all architectures, use their
641 textual representation (as produced by format) instead.
642
644 This is a procedure to write a Tcl string to a binary-encoded channel
645 as UTF-8 data preceded by a length word:
646 proc writeString {channel string} {
648 set data [encoding convertto utf-8 $string]
649 puts -nonewline [binary format Ia* \
650 [string length $data] $data]
651 }
652 This procedure reads a string from a channel that was written by the
654 previously presented writeString procedure:
655 proc readString {channel} {
657 if {![binary scan [read $channel 4] I length]} {
658 error "missing length"
659 }
660 set data [read $channel $length]
661 return [encoding convertfrom utf-8 $data]
662 }
663 This converts the contents of a file (named in the variable filename)
665 to base64 and prints them:
666 set f [open $filename rb]
668 set data [read $f]
669 close $f
670 puts [binary encode base64 -maxlen 64 $data]
671
673 encoding(n), format(n), scan(n), string(n), tcl_platform(n)
674
676 binary, format, scan
677Tcl 8.0 binary(n)