1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
1001
1002
1003
1004
1005
1006
1007
1008
1009
1010
1011
1012
1013
1014
1015
1016
1017
1018
1019
1020
1021
1022
1023
1024
1025
1026
1027
1028
1029
1030
1031
1032
1033
1034
1035
1036
1037
1038
1039
1040
1041
1042
1043
1044
1045
1046
1047
1048
1049
1050
1051
1052
1053
1054
1055
1056
1057
1058
1059
1060
1061
1062
1063
1064
1065
1066
1067
1068
1069
1070
1071
1072
1073
1074
1075
1076
1077
1078
1079
1080
1081
1082
1083
1084
1085
1086
1087
1088
1089
1090
1091
1092
1093
|
'\"
'\" Copyright (c) 1997 by Sun Microsystems, Inc.
'\" Copyright (c) 2008 by Donal K. Fellows
'\"
'\" See the file "license.terms" for information on usage and redistribution
'\" of this file, and for a DISCLAIMER OF ALL WARRANTIES.
'\"
.TH binary n 8.0 Tcl "Tcl Built-In Commands"
.so man.macros
.BS
'\" Note: do not modify the .SH NAME line immediately below!
.SH NAME
binary \- Insert and extract fields from binary strings
.SH SYNOPSIS
\fBbinary decode \fIformat\fR ?\fI\-option value ...\fR? \fIdata\fR
.br
\fBbinary encode \fIformat\fR ?\fI\-option value ...\fR? \fIdata\fR
.br
\fBbinary format \fIformatString \fR?\fIarg arg ...\fR?
.br
\fBbinary scan \fIstring formatString \fR?\fIvarName varName ...\fR?
.BE
.SH DESCRIPTION
.PP
This command provides facilities for manipulating binary data. The
subcommand \fBbinary format\fR creates a binary string from normal
Tcl values. For example, given the values 16 and 22, on a 32-bit
architecture, it might produce an 8-byte binary string consisting of
two 4-byte integers, one for each of the numbers. The subcommand
\fBbinary scan\fR, does the opposite: it extracts data
from a binary string and returns it as ordinary Tcl string values.
The \fBbinary encode\fR and \fBbinary decode\fR subcommands convert
binary data to or from string encodings such as base64 (used in MIME
messages for example).
.PP
Note that other operations on binary data, such as taking a subsequence of it,
getting its length, or reinterpreting it as a string in some encoding, are
done by other Tcl commands (respectively \fBstring range\fR,
\fBstring length\fR and \fBencoding convertfrom\fR in the example cases). A
binary string in Tcl is merely one where all the characters it contains are in
the range \eu0000\-\eu00FF.
.SH "BINARY ENCODE AND DECODE"
.PP
When encoding binary data as a readable string, the starting binary data is
passed to the \fBbinary encode\fR command, together with the name of the
encoding to use and any encoding-specific options desired. Data which has been
encoded can be converted back to binary form using \fBbinary decode\fR. The
following formats and options are supported.
.TP
\fBbase64\fR
.
The \fBbase64\fR binary encoding is commonly used in mail messages and XML
documents, and uses mostly upper and lower case letters and digits. It has the
distinction of being able to be rewrapped arbitrarily without losing
information.
.RS
.PP
During encoding, the following options are supported:
.TP
\fB\-maxlen \fIlength\fR
.
Indicates that the output should be split into lines of no more than
\fIlength\fR characters. By default, lines are not split.
.TP
\fB\-wrapchar \fIcharacter\fR
.
Indicates that, when lines are split because of the \fB\-maxlen\fR option,
\fIcharacter\fR should be used to separate lines. By default, this is a
newline character,
.QW \en .
.PP
During decoding, the following options are supported:
.TP
\fB\-strict\fR
.
Instructs the decoder to throw an error if it encounters any characters
that are not strictly part of the encoding itself. Otherwise it ignores them.
RFC 2045 calls for base64 decoders to be non-strict.
.RE
.TP
\fBhex\fR
.
The \fBhex\fR binary encoding converts each byte to a pair of hexadecimal
digits in big-endian form.
.RS
.PP
No options are supported during encoding. During decoding, the following
options are supported:
.TP
\fB\-strict\fR
.
Instructs the decoder to throw an error if it encounters whitespace characters.
Otherwise it ignores them.
.RE
.TP
\fBuuencode\fR
.
The \fBuuencode\fR binary encoding used to be common for transfer of data
between Unix systems and on USENET, but is less common these days, having been
largely superseded by the \fBbase64\fR binary encoding.
.RS
.PP
During encoding, the following options are supported (though changing them may
produce files that other implementations of decoders cannot process):
.TP
\fB\-maxlen \fIlength\fR
.
Indicates that the output should be split into lines of no more than
\fIlength\fR characters. By default, lines are split every 61 characters, and
this must be in the range 3 to 85 due to limitations in the encoding.
.TP
\fB\-wrapchar \fIcharacter\fR
.
Indicates that, when lines are split because of the \fB\-maxlen\fR option,
\fIcharacter\fR should be used to separate lines. By default, this is a
newline character,
.QW \en .
.PP
During decoding, the following options are supported:
.TP
\fB\-strict\fR
.
Instructs the decoder to throw an error if it encounters unexpected
whitespace characters. Otherwise it ignores them.
.PP
Note that neither the encoder nor the decoder handle the header and footer of
the uuencode format.
.RE
.SH "BINARY FORMAT"
.PP
The \fBbinary format\fR command generates a binary string whose layout
is specified by the \fIformatString\fR and whose contents come from
the additional arguments. The resulting binary value is returned.
.PP
The \fIformatString\fR consists of a sequence of zero or more field
specifiers separated by zero or more spaces. Each field specifier is
a single type character followed by an optional flag character followed
by an optional numeric \fIcount\fR.
Most field specifiers consume one argument to obtain the value to be
formatted. The type character specifies how the value is to be
formatted. The \fIcount\fR typically indicates how many items of the
specified type are taken from the value. If present, the \fIcount\fR
is a non-negative decimal integer or
.QW \fB*\fR ,
which normally indicates
that all of the items in the value are to be used. If the number of
arguments does not match the number of fields in the format string
that consume arguments, then an error is generated. The flag character
is ignored for \fBbinary format\fR.
.PP
Here is a small example to clarify the relation between the field
specifiers and the arguments:
.PP
.CS
\fBbinary format\fR d3d {1.0 2.0 3.0 4.0} 0.1
.CE
.PP
The first argument is a list of four numbers, but because of the count
of 3 for the associated field specifier, only the first three will be
used. The second argument is associated with the second field
specifier. The resulting binary string contains the four numbers 1.0,
2.0, 3.0 and 0.1.
.PP
Each type-count pair moves an imaginary cursor through the binary
data, storing bytes at the current position and advancing the cursor
to just after the last byte stored. The cursor is initially at
position 0 at the beginning of the data. The type may be any one of
the following characters:
.IP \fBa\fR 5
Stores a byte string of length \fIcount\fR in the output string.
Every character is taken as modulo 256 (i.e. the low byte of every
character is used, and the high byte discarded) so when storing
character strings not wholly expressible using the characters \eu0000-\eu00ff,
the \fBencoding convertto\fR command should be used first to change
the string into an external representation
if this truncation is not desired (i.e. if the characters are
not part of the ISO 8859\-1 character set.)
If \fIarg\fR has fewer than \fIcount\fR bytes, then additional zero
bytes are used to pad out the field. If \fIarg\fR is longer than the
specified length, the extra characters will be ignored. If
\fIcount\fR is
.QW \fB*\fR ,
then all of the bytes in \fIarg\fR will be
formatted. If \fIcount\fR is omitted, then one character will be
formatted. For example, the command:
.RS
.PP
.CS
\fBbinary format\fR a7a*a alpha bravo charlie
.CE
.PP
will return a binary string equivalent to:
.PP
.CS
\fBalpha\e000\e000bravoc\fR
.CE
.PP
the command:
.PP
.CS
\fBbinary format\fR a* [encoding convertto utf-8 \eu20ac]
.CE
.PP
will return a binary string equivalent to:
.PP
.CS
\fB\e342\e202\e254\fR
.CE
.PP
(which is the
UTF-8 byte sequence for a Euro-currency character), and the command:
.PP
.CS
\fBbinary format\fR a* [encoding convertto iso8859-15 \eu20ac]
.CE
.PP
will return a binary string equivalent to:
.PP
.CS
\fB\e244\fR
.CE
.PP
(which is the ISO
8859\-15 byte sequence for a Euro-currency character). Contrast these
last two with:
.PP
.CS
\fBbinary format\fR a* \eu20ac
.CE
.PP
which returns a binary string equivalent to:
.PP
.CS
\fB\e254\fR
.CE
.PP
(i.e. \fB\exac\fR) by
truncating the high-bits of the character, and which is probably not
what is desired.
.RE
.IP \fBA\fR 5
This form is the same as \fBa\fR except that spaces are used for
padding instead of nulls. For example,
.RS
.PP
.CS
\fBbinary format\fR A6A*A alpha bravo charlie
.CE
.PP
will return
.PP
.CS
\fBalpha bravoc\fR
.CE
.RE
.IP \fBb\fR 5
Stores a string of \fIcount\fR binary digits in low-to-high order
within each byte in the output binary string. \fIArg\fR must contain a
sequence of \fB1\fR and \fB0\fR characters. The resulting bytes are
emitted in first to last order with the bits being formatted in
low-to-high order within each byte. If \fIarg\fR has fewer than
\fIcount\fR digits, then zeros will be used for the remaining bits.
If \fIarg\fR has more than the specified number of digits, the extra
digits will be ignored. If \fIcount\fR is
.QW \fB*\fR ,
then all of the
digits in \fIarg\fR will be formatted. If \fIcount\fR is omitted,
then one digit will be formatted. If the number of bits formatted
does not end at a byte boundary, the remaining bits of the last byte
will be zeros. For example,
.RS
.PP
.CS
\fBbinary format\fR b5b* 11100 111000011010
.CE
.PP
will return a binary string equivalent to:
.PP
.CS
\fB\ex07\ex87\ex05\fR
.CE
.RE
.IP \fBB\fR 5
This form is the same as \fBb\fR except that the bits are stored in
high-to-low order within each byte. For example,
.RS
.PP
.CS
\fBbinary format\fR B5B* 11100 111000011010
.CE
.PP
will return a binary string equivalent to:
.PP
.CS
\fB\exe0\exe1\exa0\fR
.CE
.RE
.IP \fBH\fR 5
Stores a string of \fIcount\fR hexadecimal digits in high-to-low
within each byte in the output binary string. \fIArg\fR must contain a
sequence of characters in the set
.QW 0123456789abcdefABCDEF .
The resulting bytes are emitted in first to last order with the hex digits
being formatted in high-to-low order within each byte. If \fIarg\fR
has fewer than \fIcount\fR digits, then zeros will be used for the
remaining digits. If \fIarg\fR has more than the specified number of
digits, the extra digits will be ignored. If \fIcount\fR is
.QW \fB*\fR ,
then all of the digits in \fIarg\fR will be formatted. If
\fIcount\fR is omitted, then one digit will be formatted. If the
number of digits formatted does not end at a byte boundary, the
remaining bits of the last byte will be zeros. For example,
.RS
.PP
.CS
\fBbinary format\fR H3H*H2 ab DEF 987
.CE
.PP
will return a binary string equivalent to:
.PP
.CS
\fB\exab\ex00\exde\exf0\ex98\fR
.CE
.RE
.IP \fBh\fR 5
This form is the same as \fBH\fR except that the digits are stored in
low-to-high order within each byte. This is seldom required. For example,
.RS
.PP
.CS
\fBbinary format\fR h3h*h2 AB def 987
.CE
.PP
will return a binary string equivalent to:
.PP
.CS
\fB\exba\ex00\exed\ex0f\ex89\fR
.CE
.RE
.IP \fBc\fR 5
Stores one or more 8-bit integer values in the output string. If no
\fIcount\fR is specified, then \fIarg\fR must consist of an integer
value. If \fIcount\fR is specified, \fIarg\fR must consist of a list
containing at least that many integers. The low-order 8 bits of each integer
are stored as a one-byte value at the cursor position. If \fIcount\fR is
.QW \fB*\fR ,
then all of the integers in the list are formatted. If the
number of elements in the list is greater
than \fIcount\fR, then the extra elements are ignored. For example,
.RS
.PP
.CS
\fBbinary format\fR c3cc* {3 -3 128 1} 260 {2 5}
.CE
.PP
will return a binary string equivalent to:
.PP
.CS
\fB\ex03\exfd\ex80\ex04\ex02\ex05\fR
.CE
.PP
whereas:
.PP
.CS
\fBbinary format\fR c {2 5}
.CE
.PP
will generate an error.
.RE
.IP \fBs\fR 5
This form is the same as \fBc\fR except that it stores one or more
16-bit integers in little-endian byte order in the output string. The
low-order 16-bits of each integer are stored as a two-byte value at
the cursor position with the least significant byte stored first. For
example,
.RS
.PP
.CS
\fBbinary format\fR s3 {3 -3 258 1}
.CE
.PP
will return a binary string equivalent to:
.PP
.CS
\fB\ex03\ex00\exfd\exff\ex02\ex01\fR
.CE
.RE
.IP \fBS\fR 5
This form is the same as \fBs\fR except that it stores one or more
16-bit integers in big-endian byte order in the output string. For
example,
.RS
.PP
.CS
\fBbinary format\fR S3 {3 -3 258 1}
.CE
.PP
will return a binary string equivalent to:
.PP
.CS
\fB\ex00\ex03\exff\exfd\ex01\ex02\fR
.CE
.RE
.IP \fBt\fR 5
This form (mnemonically \fItiny\fR) is the same as \fBs\fR and \fBS\fR
except that it stores the 16-bit integers in the output string in the
native byte order of the machine where the Tcl script is running.
To determine what the native byte order of the machine is, refer to
the \fBbyteOrder\fR element of the \fBtcl_platform\fR array.
.IP \fBi\fR 5
This form is the same as \fBc\fR except that it stores one or more
32-bit integers in little-endian byte order in the output string. The
low-order 32-bits of each integer are stored as a four-byte value at
the cursor position with the least significant byte stored first. For
example,
.RS
.PP
.CS
\fBbinary format\fR i3 {3 -3 65536 1}
.CE
.PP
will return a binary string equivalent to:
.PP
.CS
\fB\ex03\ex00\ex00\ex00\exfd\exff\exff\exff\ex00\ex00\ex01\ex00\fR
.CE
.RE
.IP \fBI\fR 5
This form is the same as \fBi\fR except that it stores one or more one
or more 32-bit integers in big-endian byte order in the output string.
For example,
.RS
.PP
.CS
\fBbinary format\fR I3 {3 -3 65536 1}
.CE
.PP
will return a binary string equivalent to:
.PP
.CS
\fB\ex00\ex00\ex00\ex03\exff\exff\exff\exfd\ex00\ex01\ex00\ex00\fR
.CE
.RE
.IP \fBn\fR 5
This form (mnemonically \fInumber\fR or \fInormal\fR) is the same as
\fBi\fR and \fBI\fR except that it stores the 32-bit integers in the
output string in the native byte order of the machine where the Tcl
script is running.
To determine what the native byte order of the machine is, refer to
the \fBbyteOrder\fR element of the \fBtcl_platform\fR array.
.IP \fBw\fR 5
This form is the same as \fBc\fR except that it stores one or more
64-bit integers in little-endian byte order in the output string. The
low-order 64-bits of each integer are stored as an eight-byte value at
the cursor position with the least significant byte stored first. For
example,
.RS
.PP
.CS
\fBbinary format\fR w 7810179016327718216
.CE
.PP
will return the binary string \fBHelloTcl\fR.
.RE
.IP \fBW\fR 5
This form is the same as \fBw\fR except that it stores one or more one
or more 64-bit integers in big-endian byte order in the output string.
For example,
.RS
.PP
.CS
\fBbinary format\fR Wc 4785469626960341345 110
.CE
.PP
will return the binary string \fBBigEndian\fR
.RE
.IP \fBm\fR 5
This form (mnemonically the mirror of \fBw\fR) is the same as \fBw\fR
and \fBW\fR except that it stores the 64-bit integers in the output
string in the native byte order of the machine where the Tcl script is
running.
To determine what the native byte order of the machine is, refer to
the \fBbyteOrder\fR element of the \fBtcl_platform\fR array.
.IP \fBf\fR 5
This form is the same as \fBc\fR except that it stores one or more one
or more single-precision floating point numbers in the machine's native
representation in the output string. This representation is not
portable across architectures, so it should not be used to communicate
floating point numbers across the network. The size of a floating
point number may vary across architectures, so the number of bytes
that are generated may vary. If the value overflows the
machine's native representation, then the value of FLT_MAX
as defined by the system will be used instead. Because Tcl uses
double-precision floating point numbers internally, there may be some
loss of precision in the conversion to single-precision. For example,
on a Windows system running on an Intel Pentium processor,
.RS
.PP
.CS
\fBbinary format\fR f2 {1.6 3.4}
.CE
.PP
will return a binary string equivalent to:
.PP
.CS
\fB\excd\excc\excc\ex3f\ex9a\ex99\ex59\ex40\fR
.CE
.RE
.IP \fBr\fR 5
This form (mnemonically \fIreal\fR) is the same as \fBf\fR except that
it stores the single-precision floating point numbers in little-endian
order. This conversion only produces meaningful output when used on
machines which use the IEEE floating point representation (very
common, but not universal.)
.IP \fBR\fR 5
This form is the same as \fBr\fR except that it stores the
single-precision floating point numbers in big-endian order.
.IP \fBd\fR 5
This form is the same as \fBf\fR except that it stores one or more one
or more double-precision floating point numbers in the machine's native
representation in the output string. For example, on a
Windows system running on an Intel Pentium processor,
.RS
.PP
.CS
\fBbinary format\fR d1 {1.6}
.CE
.PP
will return a binary string equivalent to:
.PP
.CS
\fB\ex9a\ex99\ex99\ex99\ex99\ex99\exf9\ex3f\fR
.CE
.RE
.IP \fBq\fR 5
This form (mnemonically the mirror of \fBd\fR) is the same as \fBd\fR
except that it stores the double-precision floating point numbers in
little-endian order. This conversion only produces meaningful output
when used on machines which use the IEEE floating point representation
(very common, but not universal.)
.IP \fBQ\fR 5
This form is the same as \fBq\fR except that it stores the
double-precision floating point numbers in big-endian order.
.IP \fBx\fR 5
Stores \fIcount\fR null bytes in the output string. If \fIcount\fR is
not specified, stores one null byte. If \fIcount\fR is
.QW \fB*\fR ,
generates an error. This type does not consume an argument. For
example,
.RS
.PP
.CS
\fBbinary format\fR a3xa3x2a3 abc def ghi
.CE
.PP
will return a binary string equivalent to:
.PP
.CS
\fBabc\e000def\e000\e000ghi\fR
.CE
.RE
.IP \fBX\fR 5
Moves the cursor back \fIcount\fR bytes in the output string. If
\fIcount\fR is
.QW \fB*\fR
or is larger than the current cursor position,
then the cursor is positioned at location 0 so that the next byte
stored will be the first byte in the result string. If \fIcount\fR is
omitted then the cursor is moved back one byte. This type does not
consume an argument. For example,
.RS
.PP
.CS
\fBbinary format\fR a3X*a3X2a3 abc def ghi
.CE
.PP
will return \fBdghi\fR.
.RE
.IP \fB@\fR 5
Moves the cursor to the absolute location in the output string
specified by \fIcount\fR. Position 0 refers to the first byte in the
output string. If \fIcount\fR refers to a position beyond the last
byte stored so far, then null bytes will be placed in the uninitialized
locations and the cursor will be placed at the specified location. If
\fIcount\fR is
.QW \fB*\fR ,
then the cursor is moved to the current end of
the output string. If \fIcount\fR is omitted, then an error will be
generated. This type does not consume an argument. For example,
.RS
.PP
.CS
\fBbinary format\fR a5@2a1@*a3@10a1 abcde f ghi j
.CE
.PP
will return
.PP
.CS
\fBabfdeghi\e000\e000j\fR
.CE
.RE
.SH "BINARY SCAN"
.PP
The \fBbinary scan\fR command parses fields from a binary string,
returning the number of conversions performed. \fIString\fR gives the
input bytes to be parsed (one byte per character, and characters not
representable as a byte have their high bits chopped)
and \fIformatString\fR indicates how to parse it.
Each \fIvarName\fR gives the name of a variable; when a field is
scanned from \fIstring\fR the result is assigned to the corresponding
variable.
.PP
As with \fBbinary format\fR, the \fIformatString\fR consists of a
sequence of zero or more field specifiers separated by zero or more
spaces. Each field specifier is a single type character followed by
an optional flag character followed by an optional numeric \fIcount\fR.
Most field specifiers consume one
argument to obtain the variable into which the scanned values should
be placed. The type character specifies how the binary data is to be
interpreted. The \fIcount\fR typically indicates how many items of
the specified type are taken from the data. If present, the
\fIcount\fR is a non-negative decimal integer or
.QW \fB*\fR ,
which normally indicates that all of the remaining items in the data are to
be used. If there are not enough bytes left after the current cursor
position to satisfy the current field specifier, then the
corresponding variable is left untouched and \fBbinary scan\fR returns
immediately with the number of variables that were set. If there are
not enough arguments for all of the fields in the format string that
consume arguments, then an error is generated. The flag character
.QW u
may be given to cause some types to be read as unsigned values. The flag
is accepted for all field types but is ignored for non-integer fields.
.PP
A similar example as with \fBbinary format\fR should explain the
relation between field specifiers and arguments in case of the binary
scan subcommand:
.PP
.CS
\fBbinary scan\fR $bytes s3s first second
.CE
.PP
This command (provided the binary string in the variable \fIbytes\fR
is long enough) assigns a list of three integers to the variable
\fIfirst\fR and assigns a single value to the variable \fIsecond\fR.
If \fIbytes\fR contains fewer than 8 bytes (i.e. four 2-byte
integers), no assignment to \fIsecond\fR will be made, and if
\fIbytes\fR contains fewer than 6 bytes (i.e. three 2-byte integers),
no assignment to \fIfirst\fR will be made. Hence:
.PP
.CS
puts [\fBbinary scan\fR abcdefg s3s first second]
puts $first
puts $second
.CE
.PP
will print (assuming neither variable is set previously):
.PP
.CS
1
25185 25699 26213
can't read "second": no such variable
.CE
.PP
It is \fIimportant\fR to note that the \fBc\fR, \fBs\fR, and \fBS\fR
(and \fBi\fR and \fBI\fR on 64bit systems) will be scanned into
long data size values. In doing this, values that have their high
bit set (0x80 for chars, 0x8000 for shorts, 0x80000000 for ints),
will be sign extended. Thus the following will occur:
.PP
.CS
set signShort [\fBbinary format\fR s1 0x8000]
\fBbinary scan\fR $signShort s1 val; \fI# val == 0xFFFF8000\fR
.CE
.PP
If you require unsigned values you can include the
.QW u
flag character following
the field type. For example, to read an unsigned short value:
.PP
.CS
set signShort [\fBbinary format\fR s1 0x8000]
\fBbinary scan\fR $signShort su1 val; \fI# val == 0x00008000\fR
.CE
.PP
Each type-count pair moves an imaginary cursor through the binary data,
reading bytes from the current position. The cursor is initially
at position 0 at the beginning of the data. The type may be any one of
the following characters:
.IP \fBa\fR 5
The data is a byte string of length \fIcount\fR. If \fIcount\fR is
.QW \fB*\fR ,
then all of the remaining bytes in \fIstring\fR will be
scanned into the variable. If \fIcount\fR is omitted, then one
byte will be scanned.
All bytes scanned will be interpreted as being characters in the
range \eu0000-\eu00ff so the \fBencoding convertfrom\fR command will be
needed if the string is not a binary string or a string encoded in ISO
8859\-1.
For example,
.RS
.PP
.CS
\fBbinary scan\fR abcde\e000fghi a6a10 var1 var2
.CE
.PP
will return \fB1\fR with the string equivalent to \fBabcde\e000\fR
stored in \fIvar1\fR and \fIvar2\fR left unmodified, and
.PP
.CS
\fBbinary scan\fR \e342\e202\e254 a* var1
set var2 [encoding convertfrom utf-8 $var1]
.CE
.PP
will store a Euro-currency character in \fIvar2\fR.
.RE
.IP \fBA\fR 5
This form is the same as \fBa\fR, except trailing blanks and nulls are stripped from
the scanned value before it is stored in the variable. For example,
.RS
.PP
.CS
\fBbinary scan\fR "abc efghi \e000" A* var1
.CE
.PP
will return \fB1\fR with \fBabc efghi\fR stored in \fIvar1\fR.
.RE
.IP \fBb\fR 5
The data is turned into a string of \fIcount\fR binary digits in
low-to-high order represented as a sequence of
.QW 1
and
.QW 0
characters. The data bytes are scanned in first to last order with
the bits being taken in low-to-high order within each byte. Any extra
bits in the last byte are ignored. If \fIcount\fR is
.QW \fB*\fR ,
then all of the remaining bits in \fIstring\fR will be scanned. If
\fIcount\fR is omitted, then one bit will be scanned. For example,
.RS
.PP
.CS
\fBbinary scan\fR \ex07\ex87\ex05 b5b* var1 var2
.CE
.PP
will return \fB2\fR with \fB11100\fR stored in \fIvar1\fR and
\fB1110000110100000\fR stored in \fIvar2\fR.
.RE
.IP \fBB\fR 5
This form is the same as \fBb\fR, except the bits are taken in
high-to-low order within each byte. For example,
.RS
.PP
.CS
\fBbinary scan\fR \ex70\ex87\ex05 B5B* var1 var2
.CE
.PP
will return \fB2\fR with \fB01110\fR stored in \fIvar1\fR and
\fB1000011100000101\fR stored in \fIvar2\fR.
.RE
.IP \fBH\fR 5
The data is turned into a string of \fIcount\fR hexadecimal digits in
high-to-low order represented as a sequence of characters in the set
.QW 0123456789abcdef .
The data bytes are scanned in first to last
order with the hex digits being taken in high-to-low order within each
byte. Any extra bits in the last byte are ignored. If \fIcount\fR is
.QW \fB*\fR ,
then all of the remaining hex digits in \fIstring\fR will be
scanned. If \fIcount\fR is omitted, then one hex digit will be
scanned. For example,
.RS
.PP
.CS
\fBbinary scan\fR \ex07\exC6\ex05\ex1f\ex34 H3H* var1 var2
.CE
.PP
will return \fB2\fR with \fB07c\fR stored in \fIvar1\fR and
\fB051f34\fR stored in \fIvar2\fR.
.RE
.IP \fBh\fR 5
This form is the same as \fBH\fR, except the digits are taken in
reverse (low-to-high) order within each byte. For example,
.RS
.PP
.CS
\fBbinary scan\fR \ex07\ex86\ex05\ex12\ex34 h3h* var1 var2
.CE
.PP
will return \fB2\fR with \fB706\fR stored in \fIvar1\fR and
\fB502143\fR stored in \fIvar2\fR.
.PP
Note that most code that wishes to parse the hexadecimal digits from
multiple bytes in order should use the \fBH\fR format.
.RE
.IP \fBc\fR 5
The data is turned into \fIcount\fR 8-bit signed integers and stored
in the corresponding variable as a list, or as unsigned if \fBu\fR is placed
immediately after the \fBc\fR. If \fIcount\fR is
.QW \fB*\fR ,
then all of the remaining bytes in \fIstring\fR will be scanned. If
\fIcount\fR is omitted, then one 8-bit integer will be scanned. For
example,
.RS
.PP
.CS
\fBbinary scan\fR \ex07\ex86\ex05 c2c* var1 var2
.CE
.PP
will return \fB2\fR with \fB7 -122\fR stored in \fIvar1\fR and \fB5\fR
stored in \fIvar2\fR. Note that the integers returned are signed unless
\fBcu\fR in place of \fBc\fR.
.RE
.IP \fBs\fR 5
The data is interpreted as \fIcount\fR 16-bit signed integers
represented in little-endian byte order, or as unsigned if \fBu\fR is placed
immediately after the \fBs\fR. The integers are stored in
the corresponding variable as a list. If \fIcount\fR is
.QW \fB*\fR ,
then all of the remaining bytes in \fIstring\fR will be scanned. If
\fIcount\fR is omitted, then one 16-bit integer will be scanned. For
example,
.RS
.PP
.CS
\fBbinary scan\fR \ex05\ex00\ex07\ex00\exf0\exff s2s* var1 var2
.CE
.PP
will return \fB2\fR with \fB5 7\fR stored in \fIvar1\fR and \fB\-16\fR
stored in \fIvar2\fR. Note that the integers returned are signed unless
\fBsu\fR is used in place of \fBs\fR.
.RE
.IP \fBS\fR 5
This form is the same as \fBs\fR except that the data is interpreted
as \fIcount\fR 16-bit integers represented in big-endian byte
order. For example,
.RS
.PP
.CS
\fBbinary scan\fR \ex00\ex05\ex00\ex07\exff\exf0 S2S* var1 var2
.CE
.PP
will return \fB2\fR with \fB5 7\fR stored in \fIvar1\fR and \fB\-16\fR
stored in \fIvar2\fR.
.RE
.IP \fBt\fR 5
The data is interpreted as \fIcount\fR 16-bit signed integers
represented in the native byte order of the machine running the Tcl
script, or as unsigned if \fBu\fR is placed
immediately after the \fBt\fR. It is otherwise identical to \fBs\fR and \fBS\fR.
To determine what the native byte order of the machine is, refer to
the \fBbyteOrder\fR element of the \fBtcl_platform\fR array.
.IP \fBi\fR 5
The data is interpreted as \fIcount\fR 32-bit signed integers
represented in little-endian byte order, or as unsigned if \fBu\fR is placed
immediately after the \fBi\fR. The integers are stored in
the corresponding variable as a list. If \fIcount\fR is
.QW \fB*\fR ,
then all of the remaining bytes in \fIstring\fR will be scanned. If
\fIcount\fR is omitted, then one 32-bit integer will be scanned. For
example,
.RS
.PP
.CS
set str \ex05\ex00\ex00\ex00\ex07\ex00\ex00\ex00\exf0\exff\exff\exff
\fBbinary scan\fR $str i2i* var1 var2
.CE
.PP
will return \fB2\fR with \fB5 7\fR stored in \fIvar1\fR and \fB\-16\fR
stored in \fIvar2\fR. Note that the integers returned are signed unless
\fBiu\fR is used in place of \fBi\fR.
.RE
.IP \fBI\fR 5
This form is the same as \fBI\fR except that the data is interpreted
as \fIcount\fR 32-bit signed integers represented in big-endian byte
order, or as unsigned if \fBu\fR is placed
immediately after the \fBI\fR. For example,
.RS
.PP
.CS
set str \ex00\ex00\ex00\ex05\ex00\ex00\ex00\ex07\exff\exff\exff\exf0
\fBbinary scan\fR $str I2I* var1 var2
.CE
.PP
will return \fB2\fR with \fB5 7\fR stored in \fIvar1\fR and \fB\-16\fR
stored in \fIvar2\fR.
.RE
.IP \fBn\fR 5
The data is interpreted as \fIcount\fR 32-bit signed integers
represented in the native byte order of the machine running the Tcl
script, or as unsigned if \fBu\fR is placed
immediately after the \fBn\fR. It is otherwise identical to \fBi\fR and \fBI\fR.
To determine what the native byte order of the machine is, refer to
the \fBbyteOrder\fR element of the \fBtcl_platform\fR array.
.IP \fBw\fR 5
The data is interpreted as \fIcount\fR 64-bit signed integers
represented in little-endian byte order, or as unsigned if \fBu\fR is placed
immediately after the \fBw\fR. The integers are stored in
the corresponding variable as a list. If \fIcount\fR is
.QW \fB*\fR ,
then all of the remaining bytes in \fIstring\fR will be scanned. If
\fIcount\fR is omitted, then one 64-bit integer will be scanned. For
example,
.RS
.PP
.CS
set str \ex05\ex00\ex00\ex00\ex07\ex00\ex00\ex00\exf0\exff\exff\exff
\fBbinary scan\fR $str wi* var1 var2
.CE
.PP
will return \fB2\fR with \fB30064771077\fR stored in \fIvar1\fR and
\fB\-16\fR stored in \fIvar2\fR.
.RE
.IP \fBW\fR 5
This form is the same as \fBw\fR except that the data is interpreted
as \fIcount\fR 64-bit signed integers represented in big-endian byte
order, or as unsigned if \fBu\fR is placed
immediately after the \fBW\fR. For example,
.RS
.PP
.CS
set str \ex00\ex00\ex00\ex05\ex00\ex00\ex00\ex07\exff\exff\exff\exf0
\fBbinary scan\fR $str WI* var1 var2
.CE
.PP
will return \fB2\fR with \fB21474836487\fR stored in \fIvar1\fR and \fB\-16\fR
stored in \fIvar2\fR.
.RE
.IP \fBm\fR 5
The data is interpreted as \fIcount\fR 64-bit signed integers
represented in the native byte order of the machine running the Tcl
script, or as unsigned if \fBu\fR is placed
immediately after the \fBm\fR. It is otherwise identical to \fBw\fR and \fBW\fR.
To determine what the native byte order of the machine is, refer to
the \fBbyteOrder\fR element of the \fBtcl_platform\fR array.
.IP \fBf\fR 5
The data is interpreted as \fIcount\fR single-precision floating point
numbers in the machine's native representation. The floating point
numbers are stored in the corresponding variable as a list. If
\fIcount\fR is
.QW \fB*\fR ,
then all of the remaining bytes in
\fIstring\fR will be scanned. If \fIcount\fR is omitted, then one
single-precision floating point number will be scanned. The size of a
floating point number may vary across architectures, so the number of
bytes that are scanned may vary. If the data does not represent a
valid floating point number, the resulting value is undefined and
compiler dependent. For example, on a Windows system running on an
Intel Pentium processor,
.RS
.PP
.CS
\fBbinary scan\fR \ex3f\excc\excc\excd f var1
.CE
.PP
will return \fB1\fR with \fB1.6000000238418579\fR stored in
\fIvar1\fR.
.RE
.IP \fBr\fR 5
This form is the same as \fBf\fR except that the data is interpreted
as \fIcount\fR single-precision floating point number in little-endian
order. This conversion is not portable to the minority of systems not
using IEEE floating point representations.
.IP \fBR\fR 5
This form is the same as \fBf\fR except that the data is interpreted
as \fIcount\fR single-precision floating point number in big-endian
order. This conversion is not portable to the minority of systems not
using IEEE floating point representations.
.IP \fBd\fR 5
This form is the same as \fBf\fR except that the data is interpreted
as \fIcount\fR double-precision floating point numbers in the
machine's native representation. For example, on a Windows system
running on an Intel Pentium processor,
.RS
.PP
.CS
\fBbinary scan\fR \ex9a\ex99\ex99\ex99\ex99\ex99\exf9\ex3f d var1
.CE
.PP
will return \fB1\fR with \fB1.6000000000000001\fR
stored in \fIvar1\fR.
.RE
.IP \fBq\fR 5
This form is the same as \fBd\fR except that the data is interpreted
as \fIcount\fR double-precision floating point number in little-endian
order. This conversion is not portable to the minority of systems not
using IEEE floating point representations.
.IP \fBQ\fR 5
This form is the same as \fBd\fR except that the data is interpreted
as \fIcount\fR double-precision floating point number in big-endian
order. This conversion is not portable to the minority of systems not
using IEEE floating point representations.
.IP \fBx\fR 5
Moves the cursor forward \fIcount\fR bytes in \fIstring\fR. If
\fIcount\fR is
.QW \fB*\fR
or is larger than the number of bytes after the
current cursor position, then the cursor is positioned after
the last byte in \fIstring\fR. If \fIcount\fR is omitted, then the
cursor is moved forward one byte. Note that this type does not
consume an argument. For example,
.RS
.PP
.CS
\fBbinary scan\fR \ex01\ex02\ex03\ex04 x2H* var1
.CE
.PP
will return \fB1\fR with \fB0304\fR stored in \fIvar1\fR.
.RE
.IP \fBX\fR 5
Moves the cursor back \fIcount\fR bytes in \fIstring\fR. If
\fIcount\fR is
.QW \fB*\fR
or is larger than the current cursor position,
then the cursor is positioned at location 0 so that the next byte
scanned will be the first byte in \fIstring\fR. If \fIcount\fR
is omitted then the cursor is moved back one byte. Note that this
type does not consume an argument. For example,
.RS
.PP
.CS
\fBbinary scan\fR \ex01\ex02\ex03\ex04 c2XH* var1 var2
.CE
.PP
will return \fB2\fR with \fB1 2\fR stored in \fIvar1\fR and \fB020304\fR
stored in \fIvar2\fR.
.RE
.IP \fB@\fR 5
Moves the cursor to the absolute location in the data string specified
by \fIcount\fR. Note that position 0 refers to the first byte in
\fIstring\fR. If \fIcount\fR refers to a position beyond the end of
\fIstring\fR, then the cursor is positioned after the last byte. If
\fIcount\fR is omitted, then an error will be generated. For example,
.RS
.PP
.CS
\fBbinary scan\fR \ex01\ex02\ex03\ex04 c2@1H* var1 var2
.CE
.PP
will return \fB2\fR with \fB1 2\fR stored in \fIvar1\fR and \fB020304\fR
stored in \fIvar2\fR.
.RE
.SH "PORTABILITY ISSUES"
.PP
The \fBr\fR, \fBR\fR, \fBq\fR and \fBQ\fR conversions will only work
reliably for transferring data between computers which are all using
IEEE floating point representations. This is very common, but not
universal. To transfer floating-point numbers portably between all
architectures, use their textual representation (as produced by
\fBformat\fR) instead.
.SH EXAMPLES
.PP
This is a procedure to write a Tcl string to a binary-encoded channel as
UTF-8 data preceded by a length word:
.PP
.CS
proc \fIwriteString\fR {channel string} {
set data [encoding convertto utf-8 $string]
puts -nonewline [\fBbinary format\fR Ia* \e
[string length $data] $data]
}
.CE
.PP
This procedure reads a string from a channel that was written by the
previously presented \fIwriteString\fR procedure:
.PP
.CS
proc \fIreadString\fR {channel} {
if {![\fBbinary scan\fR [read $channel 4] I length]} {
error "missing length"
}
set data [read $channel $length]
return [encoding convertfrom utf-8 $data]
}
.CE
.PP
This converts the contents of a file (named in the variable \fIfilename\fR) to
base64 and prints them:
.PP
.CS
set f [open $filename rb]
set data [read $f]
close $f
puts [\fBbinary encode\fR base64 \-maxlen 64 $data]
.CE
.SH "SEE ALSO"
encoding(n), format(n), scan(n), string(n), tcl_platform(n)
.SH KEYWORDS
binary, format, scan
'\" Local Variables:
'\" mode: nroff
'\" fill-column: 78
'\" End:
|