1binary(n)                    Tcl Built-In Commands                   binary(n)
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NAME

8       binary - Insert and extract fields from binary strings
9

SYNOPSIS

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 ...?
15______________________________________________________________________________
16

DESCRIPTION

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
28       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

BINARY ENCODE AND DECODE

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
42       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
48              During encoding, the following options are supported:            │
49
50              -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
55              -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
60              During decoding, the following options are supported:            │
61
62              -strict                                                          
63                     Instructs  the decoder to throw an error if it encounters │
64                     whitespace characters. Otherwise it ignores them.         │
65
66       hex                                                                     
67              The hex binary encoding converts each byte to a pair of hexadec‐ │
68              imal digits in big-endian form.                                  │
69
70              No  options  are supported during encoding. During decoding, the │
71              following options are supported:                                 │
72
73              -strict                                                          
74                     Instructs the decoder to throw an error if it  encounters │
75                     whitespace characters. Otherwise it ignores them.         │
76
77       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
83              During encoding, the following  options  are  supported  (though │
84              changing  them  may  produce files that other implementations of │
85              decoders cannot process):                                        │
86
87              -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
93              -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
98              During decoding, the following options are supported:            │
99
100              -strict                                                          
101                     Instructs  the decoder to throw an error if it encounters │
102                     unexpected whitespace characters.  Otherwise  it  ignores │
103                     them.                                                     │
104
105              Note  that neither the encoder nor the decoder handle the header │
106              and footer of the uuencode format.                               │
107

BINARY FORMAT

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
113       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
126       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
130       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
136       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
142       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
169       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
174       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
188       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
193       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
208       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
214       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
228       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
236       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
242       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
248       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
257       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
264       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
270       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
278       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
284       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
290       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
307       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
313       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
316       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
324       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
330       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
333       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
339       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
348       @    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

BINARY SCAN

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
368       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
387       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
392       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
406       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
418       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
423       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
437       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
443       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
454       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
460       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
471       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
476            Note  that  most  code that wishes to parse the hexadecimal digits
477            from multiple bytes in order should use the H format.
478
479       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
489       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
500       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
506       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
512       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
524       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
531       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
537       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
548       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
556       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
562       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
576       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
581       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
586       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
593       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
598       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
603       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
611       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
620       @    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

PORTABILITY ISSUES

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

EXAMPLES

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
639              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
645       This  procedure  reads  a string from a channel that was written by the
646       previously presented writeString procedure:
647
648              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
656       This converts the contents of a file (named in the  variable  filename)
657       to base64 and prints them:
658
659              set f [open $filename rb]
660              set data [read $f]
661              close $f
662              puts [binary encode base64 -maxlen 64 $data]
663

SEE ALSO

665       encoding(n), format(n), scan(n), string(n), tcl_platform(n)
666

KEYWORDS

668       binary, format, scan
669
670
671
672Tcl                                   8.0                            binary(n)
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