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+= Packed \Data
+
+== Quick Reference
+
+These tables summarize the directives for packing and unpacking.
+
+=== For Integers
+
+ Directive | Meaning
+ --------------|---------------------------------------------------------------
+ C | 8-bit unsigned (unsigned char)
+ S | 16-bit unsigned, native endian (uint16_t)
+ L | 32-bit unsigned, native endian (uint32_t)
+ Q | 64-bit unsigned, native endian (uint64_t)
+ J | pointer width unsigned, native endian (uintptr_t)
+
+ c | 8-bit signed (signed char)
+ s | 16-bit signed, native endian (int16_t)
+ l | 32-bit signed, native endian (int32_t)
+ q | 64-bit signed, native endian (int64_t)
+ j | pointer width signed, native endian (intptr_t)
+
+ S_ S! | unsigned short, native endian
+ I I_ I! | unsigned int, native endian
+ L_ L! | unsigned long, native endian
+ Q_ Q! | unsigned long long, native endian
+ | (raises ArgumentError if the platform has no long long type)
+ J! | uintptr_t, native endian (same with J)
+
+ s_ s! | signed short, native endian
+ i i_ i! | signed int, native endian
+ l_ l! | signed long, native endian
+ q_ q! | signed long long, native endian
+ | (raises ArgumentError if the platform has no long long type)
+ j! | intptr_t, native endian (same with j)
+
+ S> s> S!> s!> | each the same as the directive without >, but big endian
+ L> l> L!> l!> | S> is the same as n
+ I!> i!> | L> is the same as N
+ Q> q> Q!> q!> |
+ J> j> J!> j!> |
+
+ S< s< S!< s!< | each the same as the directive without <, but little endian
+ L< l< L!< l!< | S< is the same as v
+ I!< i!< | L< is the same as V
+ Q< q< Q!< q!< |
+ J< j< J!< j!< |
+
+ n | 16-bit unsigned, network (big-endian) byte order
+ N | 32-bit unsigned, network (big-endian) byte order
+ v | 16-bit unsigned, VAX (little-endian) byte order
+ V | 32-bit unsigned, VAX (little-endian) byte order
+
+ U | UTF-8 character
+ w | BER-compressed integer
+ R | LEB128 encoded unsigned integer
+ r | LEB128 encoded signed integer
+
+=== For Floats
+
+ Directive | Meaning
+ ----------|--------------------------------------------------
+ D d | double-precision, native format
+ F f | single-precision, native format
+ E | double-precision, little-endian byte order
+ e | single-precision, little-endian byte order
+ G | double-precision, network (big-endian) byte order
+ g | single-precision, network (big-endian) byte order
+
+=== For Strings
+
+ Directive | Meaning
+ ----------|-----------------------------------------------------------------
+ A | arbitrary binary string (remove trailing nulls and ASCII spaces)
+ a | arbitrary binary string
+ Z | null-terminated string
+ B | bit string (MSB first)
+ b | bit string (LSB first)
+ H | hex string (high nibble first)
+ h | hex string (low nibble first)
+ u | UU-encoded string
+ M | quoted-printable, MIME encoding (see RFC2045)
+ m | base64 encoded string (RFC 2045) (default)
+ | (base64 encoded string (RFC 4648) if followed by 0)
+ P | pointer to a structure (fixed-length string)
+ p | pointer to a null-terminated string
+
+=== Additional Directives for Packing
+
+ Directive | Meaning
+ ----------|----------------------------------------------------------------
+ @ | moves to absolute position
+ X | back up a byte
+ x | null byte
+
+=== Additional Directives for Unpacking
+
+ Directive | Meaning
+ ----------|----------------------------------------------------------------
+ @ | skip to the offset given by the length argument
+ X | skip backward one byte
+ x | skip forward one byte
+ ^ | return the current offset
+
+== Packing and Unpacking
+
+Certain Ruby core methods deal with packing and unpacking data:
+
+- Method Array#pack:
+ Formats each element in array +self+ into a binary string;
+ returns that string.
+- Method String#unpack:
+ Extracts data from string +self+,
+ forming objects that become the elements of a new array;
+ returns that array.
+- Method String#unpack1:
+ Does the same, but unpacks and returns only the first extracted object.
+
+Each of these methods accepts a string +template+,
+consisting of zero or more _directive_ characters,
+each followed by zero or more _modifier_ characters.
+
+Examples (directive <tt>'C'</tt> specifies 'unsigned character'):
+
+ [65].pack('C') # => "A" # One element, one directive.
+ [65, 66].pack('CC') # => "AB" # Two elements, two directives.
+ [65, 66].pack('C') # => "A" # Extra element is ignored.
+ [65].pack('') # => "" # No directives.
+ [65].pack('CC') # Extra directive raises ArgumentError.
+
+ 'A'.unpack('C') # => [65] # One character, one directive.
+ 'AB'.unpack('CC') # => [65, 66] # Two characters, two directives.
+ 'AB'.unpack('C') # => [65] # Extra character is ignored.
+ 'A'.unpack('CC') # => [65, nil] # Extra directive generates nil.
+ 'AB'.unpack('') # => [] # No directives.
+
+The string +template+ may contain any mixture of valid directives
+(directive <tt>'c'</tt> specifies 'signed character'):
+
+ [65, -1].pack('cC') # => "A\xFF"
+ "A\xFF".unpack('cC') # => [65, 255]
+
+The string +template+ may contain whitespace (which is ignored)
+and comments, each of which begins with character <tt>'#'</tt>
+and continues up to and including the next following newline:
+
+ [0,1].pack(" C #foo \n C ") # => "\x00\x01"
+ "\0\1".unpack(" C #foo \n C ") # => [0, 1]
+
+Any directive may be followed by either of these modifiers:
+
+- <tt>'*'</tt> - The directive is to be applied as many times as needed:
+
+ [65, 66].pack('C*') # => "AB"
+ 'AB'.unpack('C*') # => [65, 66]
+
+- \Integer +count+ - The directive is to be applied +count+ times:
+
+ [65, 66].pack('C2') # => "AB"
+ [65, 66].pack('C3') # Raises ArgumentError.
+ 'AB'.unpack('C2') # => [65, 66]
+ 'AB'.unpack('C3') # => [65, 66, nil]
+
+ Note: Directives in <tt>%w[A a Z m]</tt> use +count+ differently;
+ see {\String Directives}[rdoc-ref:@String+Directives].
+
+If elements don't fit the provided directive, only least significant bits are encoded:
+
+ [257].pack("C").unpack("C") # => [1]
+
+== Packing Method
+
+Method Array#pack accepts optional keyword argument
++buffer+ that specifies the target string (instead of a new string):
+
+ [65, 66].pack('C*', buffer: 'foo') # => "fooAB"
+
+The method can accept a block:
+
+ # Packed string is passed to the block.
+ [65, 66].pack('C*') {|s| p s } # => "AB"
+
+== Unpacking Methods
+
+Methods String#unpack and String#unpack1 each accept
+an optional keyword argument +offset+ that specifies an offset
+into the string:
+
+ 'ABC'.unpack('C*', offset: 1) # => [66, 67]
+ 'ABC'.unpack1('C*', offset: 1) # => 66
+
+Both methods can accept a block:
+
+ # Each unpacked object is passed to the block.
+ ret = []
+ "ABCD".unpack("C*") {|c| ret << c }
+ ret # => [65, 66, 67, 68]
+
+ # The single unpacked object is passed to the block.
+ 'AB'.unpack1('C*') {|ele| p ele } # => 65
+
+== \Integer Directives
+
+Each integer directive specifies the packing or unpacking
+for one element in the input or output array.
+
+=== 8-Bit \Integer Directives
+
+- <tt>'c'</tt> - 8-bit signed integer
+ (like C <tt>signed char</tt>):
+
+ [0, 1, 255].pack('c*') # => "\x00\x01\xFF"
+ s = [0, 1, -1].pack('c*') # => "\x00\x01\xFF"
+ s.unpack('c*') # => [0, 1, -1]
+
+- <tt>'C'</tt> - 8-bit unsigned integer
+ (like C <tt>unsigned char</tt>):
+
+ [0, 1, 255].pack('C*') # => "\x00\x01\xFF"
+ s = [0, 1, -1].pack('C*') # => "\x00\x01\xFF"
+ s.unpack('C*') # => [0, 1, 255]
+
+=== 16-Bit \Integer Directives
+
+- <tt>'s'</tt> - 16-bit signed integer, native-endian
+ (like C <tt>int16_t</tt>):
+
+ [513, -514].pack('s*') # => "\x01\x02\xFE\xFD"
+ s = [513, 65022].pack('s*') # => "\x01\x02\xFE\xFD"
+ s.unpack('s*') # => [513, -514]
+
+- <tt>'S'</tt> - 16-bit unsigned integer, native-endian
+ (like C <tt>uint16_t</tt>):
+
+ [513, -514].pack('S*') # => "\x01\x02\xFE\xFD"
+ s = [513, 65022].pack('S*') # => "\x01\x02\xFE\xFD"
+ s.unpack('S*') # => [513, 65022]
+
+- <tt>'n'</tt> - 16-bit network integer, big-endian:
+
+ s = [0, 1, -1, 32767, -32768, 65535].pack('n*')
+ # => "\x00\x00\x00\x01\xFF\xFF\x7F\xFF\x80\x00\xFF\xFF"
+ s.unpack('n*')
+ # => [0, 1, 65535, 32767, 32768, 65535]
+
+- <tt>'v'</tt> - 16-bit VAX integer, little-endian:
+
+ s = [0, 1, -1, 32767, -32768, 65535].pack('v*')
+ # => "\x00\x00\x01\x00\xFF\xFF\xFF\x7F\x00\x80\xFF\xFF"
+ s.unpack('v*')
+ # => [0, 1, 65535, 32767, 32768, 65535]
+
+=== 32-Bit \Integer Directives
+
+- <tt>'l'</tt> - 32-bit signed integer, native-endian
+ (like C <tt>int32_t</tt>):
+
+ s = [67305985, -50462977].pack('l*')
+ # => "\x01\x02\x03\x04\xFF\xFE\xFD\xFC"
+ s.unpack('l*')
+ # => [67305985, -50462977]
+
+- <tt>'L'</tt> - 32-bit unsigned integer, native-endian
+ (like C <tt>uint32_t</tt>):
+
+ s = [67305985, 4244504319].pack('L*')
+ # => "\x01\x02\x03\x04\xFF\xFE\xFD\xFC"
+ s.unpack('L*')
+ # => [67305985, 4244504319]
+
+- <tt>'N'</tt> - 32-bit network integer, big-endian:
+
+ s = [0,1,-1].pack('N*')
+ # => "\x00\x00\x00\x00\x00\x00\x00\x01\xFF\xFF\xFF\xFF"
+ s.unpack('N*')
+ # => [0, 1, 4294967295]
+
+- <tt>'V'</tt> - 32-bit VAX integer, little-endian:
+
+ s = [0,1,-1].pack('V*')
+ # => "\x00\x00\x00\x00\x01\x00\x00\x00\xFF\xFF\xFF\xFF"
+ s.unpack('v*')
+ # => [0, 0, 1, 0, 65535, 65535]
+
+=== 64-Bit \Integer Directives
+
+- <tt>'q'</tt> - 64-bit signed integer, native-endian
+ (like C <tt>int64_t</tt>):
+
+ s = [578437695752307201, -506097522914230529].pack('q*')
+ # => "\x01\x02\x03\x04\x05\x06\a\b\xFF\xFE\xFD\xFC\xFB\xFA\xF9\xF8"
+ s.unpack('q*')
+ # => [578437695752307201, -506097522914230529]
+
+- <tt>'Q'</tt> - 64-bit unsigned integer, native-endian
+ (like C <tt>uint64_t</tt>):
+
+ s = [578437695752307201, 17940646550795321087].pack('Q*')
+ # => "\x01\x02\x03\x04\x05\x06\a\b\xFF\xFE\xFD\xFC\xFB\xFA\xF9\xF8"
+ s.unpack('Q*')
+ # => [578437695752307201, 17940646550795321087]
+
+=== Platform-Dependent \Integer Directives
+
+- <tt>'i'</tt> - Platform-dependent width signed integer,
+ native-endian (like C <tt>int</tt>):
+
+ s = [67305985, -50462977].pack('i*')
+ # => "\x01\x02\x03\x04\xFF\xFE\xFD\xFC"
+ s.unpack('i*')
+ # => [67305985, -50462977]
+
+- <tt>'I'</tt> - Platform-dependent width unsigned integer,
+ native-endian (like C <tt>unsigned int</tt>):
+
+ s = [67305985, -50462977].pack('I*')
+ # => "\x01\x02\x03\x04\xFF\xFE\xFD\xFC"
+ s.unpack('I*')
+ # => [67305985, 4244504319]
+
+- <tt>'j'</tt> - Pointer-width signed integer, native-endian
+ (like C <tt>intptr_t</tt>):
+
+ s = [67305985, -50462977].pack('j*')
+ # => "\x01\x02\x03\x04\x00\x00\x00\x00\xFF\xFE\xFD\xFC\xFF\xFF\xFF\xFF"
+ s.unpack('j*')
+ # => [67305985, -50462977]
+
+- <tt>'J'</tt> - Pointer-width unsigned integer, native-endian
+ (like C <tt>uintptr_t</tt>):
+
+ s = [67305985, 4244504319].pack('J*')
+ # => "\x01\x02\x03\x04\x00\x00\x00\x00\xFF\xFE\xFD\xFC\x00\x00\x00\x00"
+ s.unpack('J*')
+ # => [67305985, 4244504319]
+
+=== Other \Integer Directives
+
+- <tt>'U'</tt> - UTF-8 character:
+
+ s = [4194304].pack('U*')
+ # => "\xF8\x90\x80\x80\x80"
+ s.unpack('U*')
+ # => [4194304]
+
+- <tt>'r'</tt> - Signed LEB128-encoded integer
+ (see {Signed LEB128}[https://en.wikipedia.org/wiki/LEB128#Signed_LEB128])
+
+ s = [1, 127, -128, 16383, -16384].pack("r*")
+ # => "\x01\xFF\x00\x80\x7F\xFF\xFF\x00\x80\x80\x7F"
+ s.unpack('r*')
+ # => [1, 127, -128, 16383, -16384]
+
+- <tt>'R'</tt> - Unsigned LEB128-encoded integer
+ (see {Unsigned LEB128}[https://en.wikipedia.org/wiki/LEB128#Unsigned_LEB128])
+
+ s = [1, 127, 128, 16383, 16384].pack("R*")
+ # => "\x01\x7F\x80\x01\xFF\x7F\x80\x80\x01"
+ s.unpack('R*')
+ # => [1, 127, 128, 16383, 16384]
+
+- <tt>'w'</tt> - BER-encoded integer
+ (see {BER encoding}[https://en.wikipedia.org/wiki/X.690#BER_encoding]):
+
+ s = [1073741823].pack('w*')
+ # => "\x83\xFF\xFF\xFF\x7F"
+ s.unpack('w*')
+ # => [1073741823]
+
+=== Modifiers for \Integer Directives
+
+For the following directives, <tt>'!'</tt> or <tt>'_'</tt> modifiers may be
+suffixed as underlying platform’s native size.
+
+- <tt>'i'</tt>, <tt>'I'</tt> - C <tt>int</tt>, always native size.
+- <tt>'s'</tt>, <tt>'S'</tt> - C <tt>short</tt>.
+- <tt>'l'</tt>, <tt>'L'</tt> - C <tt>long</tt>.
+- <tt>'q'</tt>, <tt>'Q'</tt> - C <tt>long long</tt>, if available.
+- <tt>'j'</tt>, <tt>'J'</tt> - C <tt>intptr_t</tt>, always native size.
+
+Native size modifiers are silently ignored for always native size directives.
+
+The endian modifiers also may be suffixed in the directives above:
+
+- <tt>'>'</tt> - Big-endian.
+- <tt>'<'</tt> - Little-endian.
+
+== \Float Directives
+
+Each float directive specifies the packing or unpacking
+for one element in the input or output array.
+
+=== Single-Precision \Float Directives
+
+- <tt>'F'</tt> or <tt>'f'</tt> - Native format:
+
+ s = [3.0].pack('F') # => "\x00\x00@@"
+ s.unpack('F') # => [3.0]
+
+- <tt>'e'</tt> - Little-endian:
+
+ s = [3.0].pack('e') # => "\x00\x00@@"
+ s.unpack('e') # => [3.0]
+
+- <tt>'g'</tt> - Big-endian:
+
+ s = [3.0].pack('g') # => "@@\x00\x00"
+ s.unpack('g') # => [3.0]
+
+=== Double-Precision \Float Directives
+
+- <tt>'D'</tt> or <tt>'d'</tt> - Native format:
+
+ s = [3.0].pack('D') # => "\x00\x00\x00\x00\x00\x00\b@"
+ s.unpack('D') # => [3.0]
+
+- <tt>'E'</tt> - Little-endian:
+
+ s = [3.0].pack('E') # => "\x00\x00\x00\x00\x00\x00\b@"
+ s.unpack('E') # => [3.0]
+
+- <tt>'G'</tt> - Big-endian:
+
+ s = [3.0].pack('G') # => "@\b\x00\x00\x00\x00\x00\x00"
+ s.unpack('G') # => [3.0]
+
+A float directive may be infinity or not-a-number:
+
+ inf = 1.0/0.0 # => Infinity
+ [inf].pack('f') # => "\x00\x00\x80\x7F"
+ "\x00\x00\x80\x7F".unpack('f') # => [Infinity]
+
+ nan = inf/inf # => NaN
+ [nan].pack('f') # => "\x00\x00\xC0\x7F"
+ "\x00\x00\xC0\x7F".unpack('f') # => [NaN]
+
+== \String Directives
+
+Each string directive specifies the packing or unpacking
+for one byte in the input or output string.
+
+=== Binary \String Directives
+
+- <tt>'A'</tt> - Arbitrary binary string (space padded; count is width);
+ +nil+ is treated as the empty string:
+
+ ['foo'].pack('A') # => "f"
+ ['foo'].pack('A*') # => "foo"
+ ['foo'].pack('A2') # => "fo"
+ ['foo'].pack('A4') # => "foo "
+ [nil].pack('A') # => " "
+ [nil].pack('A*') # => ""
+ [nil].pack('A2') # => " "
+ [nil].pack('A4') # => " "
+
+ "foo\0".unpack('A') # => ["f"]
+ "foo\0".unpack('A4') # => ["foo"]
+ "foo\0bar".unpack('A10') # => ["foo\x00bar"] # Reads past "\0".
+ "foo ".unpack('A') # => ["f"]
+ "foo ".unpack('A4') # => ["foo"]
+ "foo".unpack('A4') # => ["foo"]
+
+ japanese = 'こんにちは'
+ japanese.size # => 5
+ japanese.bytesize # => 15
+ [japanese].pack('A') # => "\xE3"
+ [japanese].pack('A*') # => "\xE3\x81\x93\xE3\x82\x93\xE3\x81\xAB\xE3\x81\xA1\xE3\x81\xAF"
+ japanese.unpack('A') # => ["\xE3"]
+ japanese.unpack('A2') # => ["\xE3\x81"]
+ japanese.unpack('A4') # => ["\xE3\x81\x93\xE3"]
+ japanese.unpack('A*') # => ["\xE3\x81\x93\xE3\x82\x93\xE3\x81\xAB\xE3\x81\xA1\xE3\x81\xAF"]
+
+- <tt>'a'</tt> - Arbitrary binary string (null padded; count is width):
+
+ ["foo"].pack('a') # => "f"
+ ["foo"].pack('a*') # => "foo"
+ ["foo"].pack('a2') # => "fo"
+ ["foo\0"].pack('a4') # => "foo\x00"
+ [nil].pack('a') # => "\x00"
+ [nil].pack('a*') # => ""
+ [nil].pack('a2') # => "\x00\x00"
+ [nil].pack('a4') # => "\x00\x00\x00\x00"
+
+ "foo\0".unpack('a') # => ["f"]
+ "foo\0".unpack('a4') # => ["foo\x00"]
+ "foo ".unpack('a4') # => ["foo "]
+ "foo".unpack('a4') # => ["foo"]
+ "foo\0bar".unpack('a4') # => ["foo\x00"] # Reads past "\0".
+
+- <tt>'Z'</tt> - Same as <tt>'a'</tt>,
+ except that null is added or ignored with <tt>'*'</tt>:
+
+ ["foo"].pack('Z*') # => "foo\x00"
+ [nil].pack('Z*') # => "\x00"
+
+ "foo\0".unpack('Z*') # => ["foo"]
+ "foo".unpack('Z*') # => ["foo"]
+ "foo\0bar".unpack('Z*') # => ["foo"] # Does not read past "\0".
+
+=== Bit \String Directives
+
+- <tt>'B'</tt> - Bit string (high byte first):
+
+ ['11111111' + '00000000'].pack('B*') # => "\xFF\x00"
+ ['10000000' + '01000000'].pack('B*') # => "\x80@"
+
+ ['1'].pack('B0') # => ""
+ ['1'].pack('B1') # => "\x80"
+ ['1'].pack('B2') # => "\x80\x00"
+ ['1'].pack('B3') # => "\x80\x00"
+ ['1'].pack('B4') # => "\x80\x00\x00"
+ ['1'].pack('B5') # => "\x80\x00\x00"
+ ['1'].pack('B6') # => "\x80\x00\x00\x00"
+
+ "\xff\x00".unpack("B*") # => ["1111111100000000"]
+ "\x01\x02".unpack("B*") # => ["0000000100000010"]
+
+ "".unpack("B0") # => [""]
+ "\x80".unpack("B1") # => ["1"]
+ "\x80".unpack("B2") # => ["10"]
+ "\x80".unpack("B3") # => ["100"]
+
+- <tt>'b'</tt> - Bit string (low byte first):
+
+ ['11111111' + '00000000'].pack('b*') # => "\xFF\x00"
+ ['10000000' + '01000000'].pack('b*') # => "\x01\x02"
+
+ ['1'].pack('b0') # => ""
+ ['1'].pack('b1') # => "\x01"
+ ['1'].pack('b2') # => "\x01\x00"
+ ['1'].pack('b3') # => "\x01\x00"
+ ['1'].pack('b4') # => "\x01\x00\x00"
+ ['1'].pack('b5') # => "\x01\x00\x00"
+ ['1'].pack('b6') # => "\x01\x00\x00\x00"
+
+ "\xff\x00".unpack("b*") # => ["1111111100000000"]
+ "\x01\x02".unpack("b*") # => ["1000000001000000"]
+
+ "".unpack("b0") # => [""]
+ "\x01".unpack("b1") # => ["1"]
+ "\x01".unpack("b2") # => ["10"]
+ "\x01".unpack("b3") # => ["100"]
+
+=== Hex \String Directives
+
+- <tt>'H'</tt> - Hex string (high nibble first):
+
+ ['10ef'].pack('H*') # => "\x10\xEF"
+ ['10ef'].pack('H0') # => ""
+ ['10ef'].pack('H3') # => "\x10\xE0"
+ ['10ef'].pack('H5') # => "\x10\xEF\x00"
+
+ ['fff'].pack('H3') # => "\xFF\xF0"
+ ['fff'].pack('H4') # => "\xFF\xF0"
+ ['fff'].pack('H5') # => "\xFF\xF0\x00"
+ ['fff'].pack('H6') # => "\xFF\xF0\x00"
+ ['fff'].pack('H7') # => "\xFF\xF0\x00\x00"
+ ['fff'].pack('H8') # => "\xFF\xF0\x00\x00"
+
+ "\x10\xef".unpack('H*') # => ["10ef"]
+ "\x10\xef".unpack('H0') # => [""]
+ "\x10\xef".unpack('H1') # => ["1"]
+ "\x10\xef".unpack('H2') # => ["10"]
+ "\x10\xef".unpack('H3') # => ["10e"]
+ "\x10\xef".unpack('H4') # => ["10ef"]
+ "\x10\xef".unpack('H5') # => ["10ef"]
+
+- <tt>'h'</tt> - Hex string (low nibble first):
+
+ ['10ef'].pack('h*') # => "\x01\xFE"
+ ['10ef'].pack('h0') # => ""
+ ['10ef'].pack('h3') # => "\x01\x0E"
+ ['10ef'].pack('h5') # => "\x01\xFE\x00"
+
+ ['fff'].pack('h3') # => "\xFF\x0F"
+ ['fff'].pack('h4') # => "\xFF\x0F"
+ ['fff'].pack('h5') # => "\xFF\x0F\x00"
+ ['fff'].pack('h6') # => "\xFF\x0F\x00"
+ ['fff'].pack('h7') # => "\xFF\x0F\x00\x00"
+ ['fff'].pack('h8') # => "\xFF\x0F\x00\x00"
+
+ "\x01\xfe".unpack('h*') # => ["10ef"]
+ "\x01\xfe".unpack('h0') # => [""]
+ "\x01\xfe".unpack('h1') # => ["1"]
+ "\x01\xfe".unpack('h2') # => ["10"]
+ "\x01\xfe".unpack('h3') # => ["10e"]
+ "\x01\xfe".unpack('h4') # => ["10ef"]
+ "\x01\xfe".unpack('h5') # => ["10ef"]
+
+=== Pointer \String Directives
+
+- <tt>'P'</tt> - Pointer to a structure (fixed-length string):
+
+ s = ['abc'].pack('P') # => "\xE0O\x7F\xE5\xA1\x01\x00\x00"
+ s.unpack('P*') # => ["abc"]
+ ".".unpack("P") # => []
+ ("\0" * 8).unpack("P") # => [nil]
+ [nil].pack("P") # => "\x00\x00\x00\x00\x00\x00\x00\x00"
+
+- <tt>'p'</tt> - Pointer to a null-terminated string:
+
+ s = ['abc'].pack('p') # => "(\xE4u\xE5\xA1\x01\x00\x00"
+ s.unpack('p*') # => ["abc"]
+ ".".unpack("p") # => []
+ ("\0" * 8).unpack("p") # => [nil]
+ [nil].pack("p") # => "\x00\x00\x00\x00\x00\x00\x00\x00"
+
+=== Other \String Directives
+
+- <tt>'M'</tt> - Quoted printable, MIME encoding;
+ text mode, but input must use LF and output LF;
+ (see {RFC 2045}[https://www.ietf.org/rfc/rfc2045.txt]):
+
+ ["a b c\td \ne"].pack('M') # => "a b c\td =\n\ne=\n"
+ ["\0"].pack('M') # => "=00=\n"
+
+ ["a"*1023].pack('M') == ("a"*73+"=\n")*14+"a=\n" # => true
+ ("a"*73+"=\na=\n").unpack('M') == ["a"*74] # => true
+ (("a"*73+"=\n")*14+"a=\n").unpack('M') == ["a"*1023] # => true
+
+ "a b c\td =\n\ne=\n".unpack('M') # => ["a b c\td \ne"]
+ "=00=\n".unpack('M') # => ["\x00"]
+
+ "pre=31=32=33after".unpack('M') # => ["pre123after"]
+ "pre=\nafter".unpack('M') # => ["preafter"]
+ "pre=\r\nafter".unpack('M') # => ["preafter"]
+ "pre=".unpack('M') # => ["pre="]
+ "pre=\r".unpack('M') # => ["pre=\r"]
+ "pre=hoge".unpack('M') # => ["pre=hoge"]
+ "pre==31after".unpack('M') # => ["pre==31after"]
+ "pre===31after".unpack('M') # => ["pre===31after"]
+
+- <tt>'m'</tt> - Base64 encoded string;
+ count specifies input bytes between each newline,
+ rounded down to nearest multiple of 3;
+ if count is zero, no newlines are added;
+ (see {RFC 4648}[https://www.ietf.org/rfc/rfc4648.txt]):
+
+ [""].pack('m') # => ""
+ ["\0"].pack('m') # => "AA==\n"
+ ["\0\0"].pack('m') # => "AAA=\n"
+ ["\0\0\0"].pack('m') # => "AAAA\n"
+ ["\377"].pack('m') # => "/w==\n"
+ ["\377\377"].pack('m') # => "//8=\n"
+ ["\377\377\377"].pack('m') # => "////\n"
+
+ "".unpack('m') # => [""]
+ "AA==\n".unpack('m') # => ["\x00"]
+ "AAA=\n".unpack('m') # => ["\x00\x00"]
+ "AAAA\n".unpack('m') # => ["\x00\x00\x00"]
+ "/w==\n".unpack('m') # => ["\xFF"]
+ "//8=\n".unpack('m') # => ["\xFF\xFF"]
+ "////\n".unpack('m') # => ["\xFF\xFF\xFF"]
+ "A\n".unpack('m') # => [""]
+ "AA\n".unpack('m') # => ["\x00"]
+ "AA=\n".unpack('m') # => ["\x00"]
+ "AAA\n".unpack('m') # => ["\x00\x00"]
+
+ [""].pack('m0') # => ""
+ ["\0"].pack('m0') # => "AA=="
+ ["\0\0"].pack('m0') # => "AAA="
+ ["\0\0\0"].pack('m0') # => "AAAA"
+ ["\377"].pack('m0') # => "/w=="
+ ["\377\377"].pack('m0') # => "//8="
+ ["\377\377\377"].pack('m0') # => "////"
+
+ "".unpack('m0') # => [""]
+ "AA==".unpack('m0') # => ["\x00"]
+ "AAA=".unpack('m0') # => ["\x00\x00"]
+ "AAAA".unpack('m0') # => ["\x00\x00\x00"]
+ "/w==".unpack('m0') # => ["\xFF"]
+ "//8=".unpack('m0') # => ["\xFF\xFF"]
+ "////".unpack('m0') # => ["\xFF\xFF\xFF"]
+
+- <tt>'u'</tt> - UU-encoded string:
+
+ [""].pack("u") # => ""
+ ["a"].pack("u") # => "!80``\n"
+ ["aaa"].pack("u") # => "#86%A\n"
+
+ "".unpack("u") # => [""]
+ "#86)C\n".unpack("u") # => ["abc"]
+
+== Offset Directives
+
+- <tt>'@'</tt> - Begin packing at the given byte offset;
+ for packing, null fill or shrink if necessary:
+
+ [1, 2].pack("C@0C") # => "\x02"
+ [1, 2].pack("C@1C") # => "\x01\x02"
+ [1, 2].pack("C@5C") # => "\x01\x00\x00\x00\x00\x02"
+ [*1..5].pack("CCCC@2C") # => "\x01\x02\x05"
+
+ For unpacking, cannot to move to outside the string:
+
+ "\x01\x00\x00\x02".unpack("C@3C") # => [1, 2]
+ "\x00".unpack("@1C") # => [nil]
+ "\x00".unpack("@2C") # Raises ArgumentError.
+
+- <tt>'X'</tt> - For packing, shrink for the given byte offset:
+
+ [0, 1, 2].pack("CCXC") # => "\x00\x02"
+ [0, 1, 2].pack("CCX2C") # => "\x02"
+
+ For unpacking; rewind unpacking position for the given byte offset:
+
+ "\x00\x02".unpack("CCXC") # => [0, 2, 2]
+
+ Cannot to move to outside the string:
+
+ [0, 1, 2].pack("CCX3C") # Raises ArgumentError.
+ "\x00\x02".unpack("CX3C") # Raises ArgumentError.
+
+- <tt>'x'</tt> - Begin packing at after the given byte offset;
+ for packing, null fill if necessary:
+
+ [].pack("x0") # => ""
+ [].pack("x") # => "\x00"
+ [].pack("x8") # => "\x00\x00\x00\x00\x00\x00\x00\x00"
+
+ For unpacking, cannot to move to outside the string:
+
+ "\x00\x00\x02".unpack("CxC") # => [0, 2]
+ "\x00\x00\x02".unpack("x3C") # => [nil]
+ "\x00\x00\x02".unpack("x4C") # Raises ArgumentError
+
+- <tt>'^'</tt> - Only for unpacking; the current position:
+
+ "foo\0\0\0".unpack("Z*^") # => ["foo", 4]
generated by cgit v1.2.3 (git 2.25.1) at 2026-05-29 19:35:28 +0000