binary
Library for handling binary data
This module contains functions for manipulating byte-oriented binaries. Although the majority of functions could be implemented using bit-syntax, the functions in this library are highly optimized and are expected to either execute faster or consume less memory (or both) than a counterpart written in pure Erlang.
The module is implemented according to the EEP (Erlang Enhancement Proposal) 31.
Note!
The library handles byte-oriented data. Bitstrings that are not
binaries (does not contain whole octets of bits) will result in a badarg
exception being thrown from any of the functions in this
module.
Types
cp()
Opaque data-type representing a compiled search-pattern. Guaranteed to be a tuple() to allow programs to distinguish it from non precompiled search patterns.
part() = {Start :: integer() >= 0, Length :: integer()}
A representaion of a part (or range) in a binary. Start is a zero-based offset into a binary() and Length is the length of that part. As input to functions in this module, a reverse part specification is allowed, constructed with a negative Length, so that the part of the binary begins at Start + Length and is -Length long. This is useful for referencing the last N bytes of a binary as {size(Binary), -N}. The functions in this module always return part()'s with positive Length.
Functions
at(Subject, Pos) -> byte()
Subject = binary()
Pos = integer() >= 0
Returns the byte at position
(zero-based) in the binary
as an integer. If
>= byte_size(
,
a badarg
exception is raised.
bin_to_list(Subject) -> [byte()]
Subject = binary()
The same as bin_to_list(
.
bin_to_list(Subject, PosLen) -> [byte()]
Subject = binary()
PosLen = part()
Converts
to a list of byte()
s, each representing
the value of one byte. The part()
denotes which part of the
binary()
to convert. Example:
1> binary:bin_to_list(<<"erlang">>,{1,3}).
"rla"
%% or [114,108,97] in list notation.
If
in any way references outside the binary, a badarg
exception is raised.
bin_to_list(Subject, Pos, Len) -> [byte()]
Subject = binary()
Pos = integer() >= 0
Len = integer()
The same as bin_to_list(
.
compile_pattern(Pattern) -> cp()
Pattern = binary() | [binary()]
Builds an internal structure representing a compilation of a
search-pattern, later to be used in the match/3,
matches/3,
split/3 or
replace/4
functions. The cp()
returned is guaranteed to be a
tuple()
to allow programs to distinguish it from non
pre-compiled search patterns
When a list of binaries is given, it denotes a set of
alternative binaries to search for. I.e if
[<<"functional">>,<<"programming">>]
is given as
, this
means "either <<"functional">>
or
<<"programming">>
". The pattern is a set of
alternatives; when only a single binary is given, the set has
only one element. The order of alternatives in a pattern is not significant.
The list of binaries used for search alternatives shall be flat and proper.
If
is not a binary or a flat proper list of binaries with length > 0,
a badarg
exception will be raised.
copy(Subject) -> binary()
Subject = binary()
The same as copy(
.
copy(Subject, N) -> binary()
Subject = binary()
N = integer() >= 0
Creates a binary with the content of
duplicated
times.
This function will always create a new binary, even if
. By using copy/1
on a binary referencing a larger binary, one
might free up the larger binary for garbage collection.
Note!
By deliberately copying a single binary to avoid referencing a larger binary, one might, instead of freeing up the larger binary for later garbage collection, create much more binary data than needed. Sharing binary data is usually good. Only in special cases, when small parts reference large binaries and the large binaries are no longer used in any process, deliberate copying might be a good idea.
If
< 0
, a badarg
exception is raised.
decode_unsigned(Subject) -> Unsigned
Subject = binary()
Unsigned = integer() >= 0
The same as decode_unsigned(
.
decode_unsigned(Subject, Endianness) -> Unsigned
Subject = binary()
Endianness = big | little
Unsigned = integer() >= 0
Converts the binary digit representation, in big or little
endian, of a positive integer in
to an Erlang integer()
.
Example:
1> binary:decode_unsigned(<<169,138,199>>,big).
11111111
encode_unsigned(Unsigned) -> binary()
Unsigned = integer() >= 0
The same as encode_unsigned(
.
encode_unsigned(Unsigned, Endianness) -> binary()
Unsigned = integer() >= 0
Endianness = big | little
Converts a positive integer to the smallest possible representation in a binary digit representation, either big or little endian.
Example:
1> binary:encode_unsigned(11111111,big).
<<169,138,199>>
first(Subject) -> byte()
Subject = binary()
Returns the first byte of the binary
as an integer. If the
size of
is zero, a badarg
exception is raised.
last(Subject) -> byte()
Subject = binary()
Returns the last byte of the binary
as an integer. If the
size of
is zero, a badarg
exception is raised.
list_to_bin(ByteList) -> binary()
ByteList = iodata()
Works exactly as erlang:list_to_binary/1
, added for completeness.
longest_common_prefix(Binaries) -> integer() >= 0
Binaries = [binary()]
Returns the length of the longest common prefix of the
binaries in the list
. Example:
1> binary:longest_common_prefix([<<"erlang">>,<<"ergonomy">>]).
2
2> binary:longest_common_prefix([<<"erlang">>,<<"perl">>]).
0
If
is not a flat list of binaries, a badarg
exception is raised.
longest_common_suffix(Binaries) -> integer() >= 0
Binaries = [binary()]
Returns the length of the longest common suffix of the
binaries in the list
. Example:
1> binary:longest_common_suffix([<<"erlang">>,<<"fang">>]).
3
2> binary:longest_common_suffix([<<"erlang">>,<<"perl">>]).
0
If Binaries
is not a flat list of binaries, a badarg
exception is raised.
match(Subject, Pattern) -> Found | nomatch
The same as match(
.
match(Subject, Pattern, Options) -> Found | nomatch
Subject = binary()
Pattern = binary() | [binary()] | cp()
Found = part()
Options = [Option]
Option = {scope, part()}
part() = {Start :: integer() >= 0, Length :: integer()}
Searches for the first occurrence of
in
and
returns the position and length.
The function will return {Pos, Length}
for the binary
in
starting at the lowest position in
, Example:
1> binary:match(<<"abcde">>, [<<"bcde">>,<<"cd">>],[]).
{1,4}
Even though <<"cd">>
ends before
<<"bcde">>
, <<"bcde">>
begins first and is therefore the first match. If two
overlapping matches begin at the same position, the longest is
returned.
Summary of the options:
Only the given part is searched. Return values still have
offsets from the beginning of
. A negative Length
is
allowed as described in the DATA TYPES
section of this manual.
If none of the strings in
is found, the atom nomatch
is returned.
For a description of
, see
compile_pattern/1.
If {scope, {Start,Length}}
is given in the options
such that Start
is larger than the size of
Subject
, Start + Length
is less than zero or
Start + Length
is larger than the size of
Subject
, a badarg
exception is raised.
matches(Subject, Pattern) -> Found
The same as matches(
.
matches(Subject, Pattern, Options) -> Found
Subject = binary()
Pattern = binary() | [binary()] | cp()
Found = [part()]
Options = [Option]
Option = {scope, part()}
part() = {Start :: integer() >= 0, Length :: integer()}
Works like match/2
, but the
is searched until
exhausted and a list of all non-overlapping parts matching
is returned (in order).
The first and longest match is preferred to a shorter, which is illustrated by the following example:
1> binary:matches(<<"abcde">>,
[<<"bcde">>,<<"bc">>>,<<"de">>],[]).
[{1,4}]
The result shows that <<"bcde">> is selected instead of the shorter match <<"bc">> (which would have given raise to one more match,<<"de">>). This corresponds to the behavior of posix regular expressions (and programs like awk), but is not consistent with alternative matches in re (and Perl), where instead lexical ordering in the search pattern selects which string matches.
If none of the strings in pattern is found, an empty list is returned.
For a description of
, see compile_pattern/1 and for a
description of available options, see match/3.
If {scope, {
is given in the options such that
is larger than the size of
,
is
less than zero or
is larger than the size of
, a badarg
exception is raised.
part(Subject, PosLen) -> binary()
Subject = binary()
PosLen = part()
Extracts the part of the binary
described by
.
Negative length can be used to extract bytes at the end of a binary:
1> Bin = <<1,2,3,4,5,6,7,8,9,10>>.
2> binary:part(Bin,{byte_size(Bin), -5}).
<<6,7,8,9,10>>
Note!
part/2and part/3 are also available in the
erlang
module under the names binary_part/2
and
binary_part/3
. Those BIFs are allowed in guard tests.
If
in any way references outside the binary, a badarg
exception
is raised.
part(Subject, Pos, Len) -> binary()
Subject = binary()
Pos = integer() >= 0
Len = integer()
The same as part(
.
referenced_byte_size(Binary) -> integer() >= 0
Binary = binary()
If a binary references a larger binary (often described as
being a sub-binary), it can be useful to get the size of the
actual referenced binary. This function can be used in a program
to trigger the use of copy/1
. By copying a binary, one might
dereference the original, possibly large, binary which a smaller
binary is a reference to.
Example:
store(Binary, GBSet) ->
NewBin =
case binary:referenced_byte_size(Binary) of
Large when Large > 2 * byte_size(Binary) ->
binary:copy(Binary);
_ ->
Binary
end,
gb_sets:insert(NewBin,GBSet).
In this example, we chose to copy the binary content before
inserting it in the gb_sets:set()
if it references a binary more than
twice the size of the data we're going to keep. Of course
different rules for when copying will apply to different
programs.
Binary sharing will occur whenever binaries are taken apart,
this is the fundamental reason why binaries are fast,
decomposition can always be done with O(1) complexity. In rare
circumstances this data sharing is however undesirable, why this
function together with copy/1
might be useful when optimizing
for memory use.
Example of binary sharing:
1> A = binary:copy(<<1>>,100).
<<1,1,1,1,1 ...
2> byte_size(A).
100
3> binary:referenced_byte_size(A)
100
4> <<_:10/binary,B:10/binary,_/binary>> = A.
<<1,1,1,1,1 ...
5> byte_size(B).
10
6> binary:referenced_byte_size(B)
100
Note!
Binary data is shared among processes. If another process still references the larger binary, copying the part this process uses only consumes more memory and will not free up the larger binary for garbage collection. Use this kind of intrusive functions with extreme care, and only if a real problem is detected.
replace(Subject, Pattern, Replacement) -> Result
Subject = binary()
Pattern = binary() | [binary()] | cp()
Replacement = Result = binary()
The same as replace(
.
replace(Subject, Pattern, Replacement, Options) -> Result
Subject = binary()
Pattern = binary() | [binary()] | cp()
Replacement = binary()
Options = [Option]
Option = global | {scope, part()} | {insert_replaced, InsPos}
InsPos = OnePos | [OnePos]
OnePos = integer() >= 0
Result = binary()
Constructs a new binary by replacing the parts in
matching
with the content of
.
If the matching sub-part of
giving raise to the
replacement is to be inserted in the result, the option
{insert_replaced,
will insert the matching part into
at the given position (or positions) before actually
inserting
into the
. Example:
1> binary:replace(<<"abcde">>,<<"b">>,<<"[]">>,[{insert_replaced,1}]).
<<"a[b]cde">>
2> binary:replace(<<"abcde">>,[<<"b">>,<<"d">>],<<"[]">>,
[global,{insert_replaced,1}]).
<<"a[b]c[d]e">>
3> binary:replace(<<"abcde">>,[<<"b">>,<<"d">>],<<"[]">>,
[global,{insert_replaced,[1,1]}]).
<<"a[bb]c[dd]e">>
4> binary:replace(<<"abcde">>,[<<"b">>,<<"d">>],<<"[-]">>,
[global,{insert_replaced,[1,2]}]).
<<"a[b-b]c[d-d]e">>
If any position given in
is greater than the size of the replacement binary, a badarg
exception is raised.
The options global
and {scope, part()}
work as for split/3. The return type is always a binary()
.
For a description of
, see compile_pattern/1.
split(Subject, Pattern) -> Parts
Subject = binary()
Pattern = binary() | [binary()] | cp()
Parts = [binary()]
The same as split(
.
split(Subject, Pattern, Options) -> Parts
Subject = binary()
Pattern = binary() | [binary()] | cp()
Options = [Option]
Option = {scope, part()} | trim | global | trim_all
Parts = [binary()]
Splits
into a list of binaries based on
. If
the option global is not given, only the first occurrence of
in
will give rise to a split.
The parts of
actually found in
are not included in the result.
Example:
1> binary:split(<<1,255,4,0,0,0,2,3>>, [<<0,0,0>>,<<2>>],[]).
[<<1,255,4>>, <<2,3>>]
2> binary:split(<<0,1,0,0,4,255,255,9>>, [<<0,0>>, <<255,255>>],[global]).
[<<0,1>>,<<4>>,<<9>>]
Summary of options:
Works as in match/3 and matches/3. Note that this only defines the scope of the search for matching strings, it does not cut the binary before splitting. The bytes before and after the scope will be kept in the result. See example below.
Removes trailing empty parts of the result (as does trim in re:split/3
)
Removes all empty parts of the result.
Repeats the split until the
is
exhausted. Conceptually the global option makes split work on
the positions returned by matches/3,
while it normally
works on the position returned by
match/3.
Example of the difference between a scope and taking the binary apart before splitting:
1> binary:split(<<"banana">>,[<<"a">>],[{scope,{2,3}}]).
[<<"ban">>,<<"na">>]
2> binary:split(binary:part(<<"banana">>,{2,3}),[<<"a">>],[]).
[<<"n">>,<<"n">>]
The return type is always a list of binaries that are all
referencing
. This means that the data in
is not
actually copied to new binaries and that
cannot be
garbage collected until the results of the split are no longer
referenced.
For a description of
, see compile_pattern/1.