Ruby Array.pack用法及代码示例

pack( aTemplateString ) → aBinaryString

pack( aTemplateString, buffer: aBufferString ) → aBufferString

根据 aTemplateString 中的指令将 arr 的内容打包成二进制序列(见下表) 指令 “A,” “a,” 和 “Z” 后面可以跟一个计数，它给出了结果的宽度场地。剩余的指令也可以进行计数，指示要转换的数组元素的数量。如果计数是星号(“*”)，则将转换所有剩余的数组元素。任何指令“sSiIlL”可以后跟下划线(“_”)或感叹号(“!”)，以使用指定类型的底层平台的本机大小；否则，它们使用与平台无关的大小。模板字符串中的空格被忽略。另见 String#unpack 。

a = [ "a", "b", "c" ]
n = [ 65, 66, 67 ]
a.pack("A3A3A3")   #=> "a  b  c  "
a.pack("a3a3a3")   #=> "a\000\000b\000\000c\000\000"
n.pack("ccc")      #=> "ABC"

如果指定了aBufferString，并且其容量足够，则pack将其用作缓冲区并返回。当偏移量由 aTemplateString 的开头指定时，结果填充在偏移量之后。如果 aBufferString 的原始内容存在并且比偏移量长，则 offsetOfBuffer 的其余部分被结果覆盖。如果它更短，则用“\0”填充空白。

# packed data is appended by default
[255].pack("C", buffer:"foo".b) #=> "foo\xFF"

# "@0" (offset 0) specifies that packed data is filled from beginning.
# Also, original data after packed data is removed. ("oo" is removed.)
[255].pack("@0C", buffer:"foo".b) #=> "\xFF"

# If the offset is bigger than the original length, \x00 is filled.
[255].pack("@5C", buffer:"foo".b) #=> "foo\x00\x00\xFF"

请注意，“buffer:” 选项不保证不会在 pack 中分配内存。如果aBufferString的容量不够，pack分配内存。

pack 的指令。

Integer       | Array   |
Directive     | Element | Meaning
----------------------------------------------------------------------------
C             | Integer | 8-bit unsigned (unsigned char)
S             | Integer | 16-bit unsigned, native endian (uint16_t)
L             | Integer | 32-bit unsigned, native endian (uint32_t)
Q             | Integer | 64-bit unsigned, native endian (uint64_t)
J             | Integer | pointer width unsigned, native endian (uintptr_t)
              |         | (J is available since Ruby 2.3.)
              |         |
c             | Integer | 8-bit signed (signed char)
s             | Integer | 16-bit signed, native endian (int16_t)
l             | Integer | 32-bit signed, native endian (int32_t)
q             | Integer | 64-bit signed, native endian (int64_t)
j             | Integer | pointer width signed, native endian (intptr_t)
              |         | (j is available since Ruby 2.3.)
              |         |
S_ S!         | Integer | unsigned short, native endian
I I_ I!       | Integer | unsigned int, native endian
L_ L!         | Integer | unsigned long, native endian
Q_ Q!         | Integer | unsigned long long, native endian (ArgumentError
              |         | if the platform has no long long type.)
              |         | (Q_ and Q! is available since Ruby 2.1.)
J!            | Integer | uintptr_t, native endian (same with J)
              |         | (J! is available since Ruby 2.3.)
              |         |
s_ s!         | Integer | signed short, native endian
i i_ i!       | Integer | signed int, native endian
l_ l!         | Integer | signed long, native endian
q_ q!         | Integer | signed long long, native endian (ArgumentError
              |         | if the platform has no long long type.)
              |         | (q_ and q! is available since Ruby 2.1.)
j!            | Integer | intptr_t, native endian (same with j)
              |         | (j! is available since Ruby 2.3.)
              |         |
S> s> S!> s!> | Integer | same as the directives without ">" except
L> l> L!> l!> |         | big endian
I!> i!>       |         | (available since Ruby 1.9.3)
Q> q> Q!> q!> |         | "S>" is the same as "n"
J> j> J!> j!> |         | "L>" is the same as "N"
              |         |
S< s< S!< s!< | Integer | same as the directives without "<" except
L< l< L!< l!< |         | little endian
I!< i!<       |         | (available since Ruby 1.9.3)
Q< q< Q!< q!< |         | "S<" is the same as "v"
J< j< J!< j!< |         | "L<" is the same as "V"
              |         |
n             | Integer | 16-bit unsigned, network (big-endian) byte order
N             | Integer | 32-bit unsigned, network (big-endian) byte order
v             | Integer | 16-bit unsigned, VAX (little-endian) byte order
V             | Integer | 32-bit unsigned, VAX (little-endian) byte order
              |         |
U             | Integer | UTF-8 character
w             | Integer | BER-compressed integer

Float        | Array   |
Directive    | Element | Meaning
---------------------------------------------------------------------------
D d          | Float   | double-precision, native format
F f          | Float   | single-precision, native format
E            | Float   | double-precision, little-endian byte order
e            | Float   | single-precision, little-endian byte order
G            | Float   | double-precision, network (big-endian) byte order
g            | Float   | single-precision, network (big-endian) byte order

String       | Array   |
Directive    | Element | Meaning
---------------------------------------------------------------------------
A            | String  | arbitrary binary string (space padded, count is width)
a            | String  | arbitrary binary string (null padded, count is width)
Z            | String  | same as ``a'', except that null is added with *
B            | String  | bit string (MSB first)
b            | String  | bit string (LSB first)
H            | String  | hex string (high nibble first)
h            | String  | hex string (low nibble first)
u            | String  | UU-encoded string
M            | String  | quoted printable, MIME encoding (see also RFC2045)
             |         | (text mode but input must use LF and output LF)
m            | String  | base64 encoded string (see RFC 2045)
             |         | (if count is 0, no line feed are added, see RFC 4648)
             |         | (count specifies input bytes between each LF,
             |         | rounded down to nearest multiple of 3)
P            | String  | pointer to a structure (fixed-length string)
p            | String  | pointer to a null-terminated string

Misc.        | Array   |
Directive    | Element | Meaning
---------------------------------------------------------------------------
@            | ---     | moves to absolute position
X            | ---     | back up a byte
x            | ---     | null byte