1binary(3) Erlang Module Definition binary(3)
2
6 binary - Library for handling binary data.
7
9 This module contains functions for manipulating byte-oriented binaries.
10 Although the majority of functions could be provided using bit-syntax,
11 the functions in this library are highly optimized and are expected to
12 either execute faster or consume less memory, or both, than a counter‐
13 part written in pure Erlang.
14 The module is provided according to Erlang Enhancement Proposal (EEP)
16 31.
17 Note:
19 The library handles byte-oriented data. For bitstrings that are not bi‐
20 naries (does not contain whole octets of bits) a badarg exception is
21 thrown from any of the functions in this module.
22
25 cp()
26 Opaque data type representing a compiled search pattern. Guaran‐
28 teed to be a tuple() to allow programs to distinguish it from
29 non-precompiled search patterns.
30 part() = {Start :: integer() >= 0, Length :: integer()}
32 A representation of a part (or range) in a binary. Start is a
34 zero-based offset into a binary() and Length is the length of
35 that part. As input to functions in this module, a reverse part
36 specification is allowed, constructed with a negative Length, so
37 that the part of the binary begins at Start + Length and is
38 -Length long. This is useful for referencing the last N bytes of
39 a binary as {size(Binary), -N}. The functions in this module al‐
40 ways return part()s with positive Length.
41
43 at(Subject, Pos) -> byte()
44 Types:
46 Subject = binary()
48 Pos = integer() >= 0
49 Returns the byte at position Pos (zero-based) in binary Subject
51 as an integer. If Pos >= byte_size(Subject), a badarg exception
52 is raised.
53 bin_to_list(Subject) -> [byte()]
55 Types:
57 Subject = binary()
59 Same as bin_to_list(Subject, {0,byte_size(Subject)}).
61 bin_to_list(Subject, PosLen) -> [byte()]
63 Types:
65 Subject = binary()
67 PosLen = part()
68 Converts Subject to a list of byte()s, each representing the
70 value of one byte. part() denotes which part of the binary() to
71 convert.
72 Example:
74 1> binary:bin_to_list(<<"erlang">>, {1,3}).
76 "rla"
77 %% or [114,108,97] in list notation.
78 If PosLen in any way references outside the binary, a badarg ex‐
80 ception is raised.
81 bin_to_list(Subject, Pos, Len) -> [byte()]
83 Types:
85 Subject = binary()
87 Pos = integer() >= 0
88 Len = integer()
89 Same as bin_to_list(Subject, {Pos, Len}).
91 compile_pattern(Pattern) -> cp()
93 Types:
95 Pattern = binary() | [binary()]
97 Builds an internal structure representing a compilation of a
99 search pattern, later to be used in functions match/3,
100 matches/3, split/3, or replace/4. The cp() returned is guaran‐
101 teed to be a tuple() to allow programs to distinguish it from
102 non-precompiled search patterns.
103 When a list of binaries is specified, it denotes a set of alter‐
105 native binaries to search for. For example, if [<<"func‐
106 tional">>,<<"programming">>] is specified as Pattern, this means
107 either <<"functional">> or <<"programming">>". The pattern is a
108 set of alternatives; when only a single binary is specified, the
109 set has only one element. The order of alternatives in a pattern
110 is not significant.
111 The list of binaries used for search alternatives must be flat
113 and proper.
114 If Pattern is not a binary or a flat proper list of binaries
116 with length > 0, a badarg exception is raised.
117 copy(Subject) -> binary()
119 Types:
121 Subject = binary()
123 Same as copy(Subject, 1).
125 copy(Subject, N) -> binary()
127 Types:
129 Subject = binary()
131 N = integer() >= 0
132 Creates a binary with the content of Subject duplicated N times.
134 This function always creates a new binary, even if N = 1. By us‐
136 ing copy/1 on a binary referencing a larger binary, one can free
137 up the larger binary for garbage collection.
138 Note:
140 By deliberately copying a single binary to avoid referencing a
141 larger binary, one can, instead of freeing up the larger binary
142 for later garbage collection, create much more binary data than
143 needed. Sharing binary data is usually good. Only in special
144 cases, when small parts reference large binaries and the large
145 binaries are no longer used in any process, deliberate copying
146 can be a good idea.
147 If N < 0, a badarg exception is raised.
150 decode_unsigned(Subject) -> Unsigned
152 Types:
154 Subject = binary()
156 Unsigned = integer() >= 0
157 Same as decode_unsigned(Subject, big).
159 decode_unsigned(Subject, Endianness) -> Unsigned
161 Types:
163 Subject = binary()
165 Endianness = big | little
166 Unsigned = integer() >= 0
167 Converts the binary digit representation, in big endian or lit‐
169 tle endian, of a positive integer in Subject to an Erlang inte‐
170 ger().
171 Example:
173 1> binary:decode_unsigned(<<169,138,199>>,big).
175 11111111
176 encode_unsigned(Unsigned) -> binary()
178 Types:
180 Unsigned = integer() >= 0
182 Same as encode_unsigned(Unsigned, big).
184 encode_unsigned(Unsigned, Endianness) -> binary()
186 Types:
188 Unsigned = integer() >= 0
190 Endianness = big | little
191 Converts a positive integer to the smallest possible representa‐
193 tion in a binary digit representation, either big endian or lit‐
194 tle endian.
195 Example:
197 1> binary:encode_unsigned(11111111, big).
199 <<169,138,199>>
200 encode_hex(Bin) -> Bin2
202 Types:
204 Bin = binary()
206 Bin2 = <<_:_*16>>
207 Encodes a binary into a hex encoded binary.
209 Example:
211 1> binary:encode_hex(<<"f">>).
213 <<"66">>
214 decode_hex(Bin) -> Bin2
216 Types:
218 Bin = <<_:_*16>>
220 Bin2 = binary()
221 Decodes a hex encoded binary into a binary.
223 Example
225 1> binary:decode_hex(<<"66">>).
227 <<"f">>
228 first(Subject) -> byte()
230 Types:
232 Subject = binary()
234 Returns the first byte of binary Subject as an integer. If the
236 size of Subject is zero, a badarg exception is raised.
237 last(Subject) -> byte()
239 Types:
241 Subject = binary()
243 Returns the last byte of binary Subject as an integer. If the
245 size of Subject is zero, a badarg exception is raised.
246 list_to_bin(ByteList) -> binary()
248 Types:
250 ByteList = iolist()
252 Works exactly as erlang:list_to_binary/1, added for complete‐
254 ness.
255 longest_common_prefix(Binaries) -> integer() >= 0
257 Types:
259 Binaries = [binary()]
261 Returns the length of the longest common prefix of the binaries
263 in list Binaries.
264 Example:
266 1> binary:longest_common_prefix([<<"erlang">>, <<"ergonomy">>]).
268 2
269 2> binary:longest_common_prefix([<<"erlang">>, <<"perl">>]).
270 0
271 If Binaries is not a flat list of binaries, a badarg exception
273 is raised.
274 longest_common_suffix(Binaries) -> integer() >= 0
276 Types:
278 Binaries = [binary()]
280 Returns the length of the longest common suffix of the binaries
282 in list Binaries.
283 Example:
285 1> binary:longest_common_suffix([<<"erlang">>, <<"fang">>]).
287 3
288 2> binary:longest_common_suffix([<<"erlang">>, <<"perl">>]).
289 0
290 If Binaries is not a flat list of binaries, a badarg exception
292 is raised.
293 match(Subject, Pattern) -> Found | nomatch
295 Types:
297 Subject = binary()
299 Pattern = binary() | [binary()] | cp()
300 Found = part()
301 Same as match(Subject, Pattern, []).
303 match(Subject, Pattern, Options) -> Found | nomatch
305 Types:
307 Subject = binary()
309 Pattern = binary() | [binary()] | cp()
310 Found = part()
311 Options = [Option]
312 Option = {scope, part()}
313 part() = {Start :: integer() >= 0, Length :: integer()}
314 Searches for the first occurrence of Pattern in Subject and re‐
316 turns the position and length.
317 The function returns {Pos, Length} for the binary in Pattern,
319 starting at the lowest position in Subject.
320 Example:
322 1> binary:match(<<"abcde">>, [<<"bcde">>, <<"cd">>],[]).
324 {1,4}
325 Even though <<"cd">> ends before <<"bcde">>, <<"bcde">> begins
327 first and is therefore the first match. If two overlapping
328 matches begin at the same position, the longest is returned.
329 Summary of the options:
331 {scope, {Start, Length}}:
333 Only the specified part is searched. Return values still
334 have offsets from the beginning of Subject. A negative
335 Length is allowed as described in section Data Types in this
336 manual.
337 If none of the strings in Pattern is found, the atom nomatch is
339 returned.
340 For a description of Pattern, see function compile_pattern/1.
342 If {scope, {Start,Length}} is specified in the options such that
344 Start > size of Subject, Start + Length < 0 or Start + Length >
345 size of Subject, a badarg exception is raised.
346 matches(Subject, Pattern) -> Found
348 Types:
350 Subject = binary()
352 Pattern = binary() | [binary()] | cp()
353 Found = [part()]
354 Same as matches(Subject, Pattern, []).
356 matches(Subject, Pattern, Options) -> Found
358 Types:
360 Subject = binary()
362 Pattern = binary() | [binary()] | cp()
363 Found = [part()]
364 Options = [Option]
365 Option = {scope, part()}
366 part() = {Start :: integer() >= 0, Length :: integer()}
367 As match/2, but Subject is searched until exhausted and a list
369 of all non-overlapping parts matching Pattern is returned (in
370 order).
371 The first and longest match is preferred to a shorter, which is
373 illustrated by the following example:
374 1> binary:matches(<<"abcde">>,
376 [<<"bcde">>,<<"bc">>,<<"de">>],[]).
377 [{1,4}]
378 The result shows that <<"bcde">> is selected instead of the
380 shorter match <<"bc">> (which would have given raise to one more
381 match, <<"de">>). This corresponds to the behavior of POSIX reg‐
382 ular expressions (and programs like awk), but is not consistent
383 with alternative matches in re (and Perl), where instead lexical
384 ordering in the search pattern selects which string matches.
385 If none of the strings in a pattern is found, an empty list is
387 returned.
388 For a description of Pattern, see compile_pattern/1. For a de‐
390 scription of available options, see match/3.
391 If {scope, {Start,Length}} is specified in the options such that
393 Start > size of Subject, Start + Length < 0 or Start + Length is
394 > size of Subject, a badarg exception is raised.
395 part(Subject, PosLen) -> binary()
397 Types:
399 Subject = binary()
401 PosLen = part()
402 Extracts the part of binary Subject described by PosLen.
404 A negative length can be used to extract bytes at the end of a
406 binary:
407 1> Bin = <<1,2,3,4,5,6,7,8,9,10>>.
409 2> binary:part(Bin, {byte_size(Bin), -5}).
410 <<6,7,8,9,10>>
411 Note:
413 part/2 and part/3 are also available in the erlang module under
414 the names binary_part/2 and binary_part/3. Those BIFs are al‐
415 lowed in guard tests.
416 If PosLen in any way references outside the binary, a badarg ex‐
419 ception is raised.
420 part(Subject, Pos, Len) -> binary()
422 Types:
424 Subject = binary()
426 Pos = integer() >= 0
427 Len = integer()
428 Same as part(Subject, {Pos, Len}).
430 referenced_byte_size(Binary) -> integer() >= 0
432 Types:
434 Binary = binary()
436 If a binary references a larger binary (often described as being
438 a subbinary), it can be useful to get the size of the referenced
439 binary. This function can be used in a program to trigger the
440 use of copy/1. By copying a binary, one can dereference the
441 original, possibly large, binary that a smaller binary is a ref‐
442 erence to.
443 Example:
445 store(Binary, GBSet) ->
447 NewBin =
448 case binary:referenced_byte_size(Binary) of
449 Large when Large > 2 * byte_size(Binary) ->
450 binary:copy(Binary);
451 _ ->
452 Binary
453 end,
454 gb_sets:insert(NewBin,GBSet).
455 In this example, we chose to copy the binary content before in‐
457 serting it in gb_sets:set() if it references a binary more than
458 twice the data size we want to keep. Of course, different rules
459 apply when copying to different programs.
460 Binary sharing occurs whenever binaries are taken apart. This is
462 the fundamental reason why binaries are fast, decomposition can
463 always be done with O(1) complexity. In rare circumstances this
464 data sharing is however undesirable, why this function together
465 with copy/1 can be useful when optimizing for memory use.
466 Example of binary sharing:
468 1> A = binary:copy(<<1>>, 100).
470 <<1,1,1,1,1 ...
471 2> byte_size(A).
472 100
473 3> binary:referenced_byte_size(A).
474 100
475 4> <<B:10/binary, C:90/binary>> = A.
476 <<1,1,1,1,1 ...
477 5> {byte_size(B), binary:referenced_byte_size(B)}.
478 {10,10}
479 6> {byte_size(C), binary:referenced_byte_size(C)}.
480 {90,100}
481 In the above example, the small binary B was copied while the
483 larger binary C references binary A.
484 Note:
486 Binary data is shared among processes. If another process still
487 references the larger binary, copying the part this process uses
488 only consumes more memory and does not free up the larger binary
489 for garbage collection. Use this kind of intrusive functions
490 with extreme care and only if a real problem is detected.
491 replace(Subject, Pattern, Replacement) -> Result
494 Types:
496 Subject = binary()
498 Pattern = binary() | [binary()] | cp()
499 Replacement = Result = binary()
500 Same as replace(Subject, Pattern, Replacement,[]).
502 replace(Subject, Pattern, Replacement, Options) -> Result
504 Types:
506 Subject = binary()
508 Pattern = binary() | [binary()] | cp()
509 Replacement = binary()
510 Options = [Option]
511 Option = global | {scope, part()} | {insert_replaced, InsPos}
512 InsPos = OnePos | [OnePos]
513 OnePos = integer() >= 0
514 An integer() =< byte_size(Replacement)
515 Result = binary()
516 Constructs a new binary by replacing the parts in Subject match‐
518 ing Pattern with the content of Replacement.
519 If the matching subpart of Subject giving raise to the replace‐
521 ment is to be inserted in the result, option {insert_replaced,
522 InsPos} inserts the matching part into Replacement at the speci‐
523 fied position (or positions) before inserting Replacement into
524 Subject.
525 Example:
527 1> binary:replace(<<"abcde">>,<<"b">>,<<"[]">>, [{insert_replaced,1}]).
529 <<"a[b]cde">>
530 2> binary:replace(<<"abcde">>,[<<"b">>,<<"d">>],<<"[]">>,[global,{insert_replaced,1}]).
531 <<"a[b]c[d]e">>
532 3> binary:replace(<<"abcde">>,[<<"b">>,<<"d">>],<<"[]">>,[global,{insert_replaced,[1,1]}]).
533 <<"a[bb]c[dd]e">>
534 4> binary:replace(<<"abcde">>,[<<"b">>,<<"d">>],<<"[-]">>,[global,{insert_replaced,[1,2]}]).
535 <<"a[b-b]c[d-d]e">>
536 If any position specified in InsPos > size of the replacement
538 binary, a badarg exception is raised.
539 Options global and {scope, part()} work as for split/3. The re‐
541 turn type is always a binary().
542 For a description of Pattern, see compile_pattern/1.
544 split(Subject, Pattern) -> Parts
546 Types:
548 Subject = binary()
550 Pattern = binary() | [binary()] | cp()
551 Parts = [binary()]
552 Same as split(Subject, Pattern, []).
554 split(Subject, Pattern, Options) -> Parts
556 Types:
558 Subject = binary()
560 Pattern = binary() | [binary()] | cp()
561 Options = [Option]
562 Option = {scope, part()} | trim | global | trim_all
563 Parts = [binary()]
564 Splits Subject into a list of binaries based on Pattern. If op‐
566 tion global is not specified, only the first occurrence of Pat‐
567 tern in Subject gives rise to a split.
568 The parts of Pattern found in Subject are not included in the
570 result.
571 Example:
573 1> binary:split(<<1,255,4,0,0,0,2,3>>, [<<0,0,0>>,<<2>>],[]).
575 [<<1,255,4>>, <<2,3>>]
576 2> binary:split(<<0,1,0,0,4,255,255,9>>, [<<0,0>>, <<255,255>>],[global]).
577 [<<0,1>>,<<4>>,<<9>>]
578 Summary of options:
580 {scope, part()}:
582 Works as in match/3 and matches/3. Notice that this only de‐
583 fines the scope of the search for matching strings, it does
584 not cut the binary before splitting. The bytes before and
585 after the scope are kept in the result. See the example be‐
586 low.
587 trim:
589 Removes trailing empty parts of the result (as does trim in
590 re:split/3.
591 trim_all:
593 Removes all empty parts of the result.
594 global:
596 Repeats the split until Subject is exhausted. Conceptually
597 option global makes split work on the positions returned by
598 matches/3, while it normally works on the position returned
599 by match/3.
600 Example of the difference between a scope and taking the binary
602 apart before splitting:
603 1> binary:split(<<"banana">>, [<<"a">>],[{scope,{2,3}}]).
605 [<<"ban">>,<<"na">>]
606 2> binary:split(binary:part(<<"banana">>,{2,3}), [<<"a">>],[]).
607 [<<"n">>,<<"n">>]
608 The return type is always a list of binaries that are all refer‐
610 encing Subject. This means that the data in Subject is not
611 copied to new binaries, and that Subject cannot be garbage col‐
612 lected until the results of the split are no longer referenced.
613 For a description of Pattern, see compile_pattern/1.
615Ericsson AB stdlib 4.3.1.3 binary(3)