PHP 二进制 pack() unpack()

PHP 5.6.3 此版本加入"q", "Q", "J",低于此版本均不能使用
#5.6.3  The "q", "Q", "J" and "P" codes were added to enable working with 64-bit numbers.
#5.5.0  The "Z" code was added with equivalent functionality to "a" for Perl compatibility.

参数列表
Code    Description
a   NUL-padded string
A   SPACE-padded string
h   Hex string, low nibble first
H   Hex string, high nibble first
c   signed char
C   unsigned char
s   signed short (always 16 bit, machine byte order)
S   unsigned short (always 16 bit, machine byte order)
n   unsigned short (always 16 bit, big endian byte order)
v   unsigned short (always 16 bit, little endian byte order)
i   signed integer (machine dependent size and byte order)
I   unsigned integer (machine dependent size and byte order)
l   signed long (always 32 bit, machine byte order)
L   unsigned long (always 32 bit, machine byte order)
N   unsigned long (always 32 bit, big endian byte order)
V   unsigned long (always 32 bit, little endian byte order)
q   signed long long (always 64 bit, machine byte order)
Q   unsigned long long (always 64 bit, machine byte order)
J   unsigned long long (always 64 bit, big endian byte order)
P   unsigned long long (always 64 bit, little endian byte order)
f   float (machine dependent size and representation)
d   double (machine dependent size and representation)
x   NUL byte
X   Back up one byte
Z   NUL-padded string (new in PHP 5.5)
@   NUL-fill to absolute position

关于Pack:
string pack ( string $format [, mixed $args [, mixed $... ]] )

下面的第一部分把数字值包装成字节：
$out = pack("CCCC", 65, 66, 67, 68);      # $out 等于"ABCD"
$out = pack("C4", 65, 66, 67, 68);        # 一样的东西

下面的对 Unicode 的循环字母做同样的事情：
$foo = pack("U4", 0x24b6, 0x24b7, 0x24b8, 0x24b9);

下面的做类似的事情，增加了一些空：
$out = pack("CCxxCC", 65, 66, 67, 68);   # $out 等于 "AB\0\0CD"

打包你的短整数并不意味着你就可移植了：
$out = pack("s2", 1, 2);
# 在小头在前的机器上是 "\1\0\2\0"
# 在大头在前的机器上是 "\0\1\0\2"

在二进制和十六进制包装上，count 指的是位或者半字节的数量，而不是生成的字节数量：
$out = pack("B32", "...");
$out = pack("H8", "5065726c");         # 都生成“Perl”

a 域里的长度只应用于一个字串：
$out = pack("a4", "abcd", "x", "y", "z");      # "abcd"

要绕开这个限制，使用多倍声明：
$out = pack("aaaa",    "abcd", "x", "y", "z");   # "axyz"
$out = pack("a" x 4,   "abcd", "x", "y", "z
aa8d
");   # "axyz"

a 格式做空填充：
$out = pack("a14", "abcdefg");    # " abcdefg\0\0\0\0\0\0"

关于unpack:
array unpack ( string $format, string $data )

$data = "010000020007";
unpack("Sint1/Cchar1/Sint2/Cchar2",$data);

# array('int1'=>1, 'char1'=>'0','int2'=>2,'char2'=>7);

举例  协议格式如下：

包头(2bytes)+加密(1byte)+命令码(2bytes)+帧内容
1.包头的内容是记录帧内容的长度;
2.加密:0表示不加密，1表示加密；
3.命令码为服务端命令识别符号；

使用pack/unpack 举例程序代码为 ：
$lastact   = pack('SCSa32a32',0x0040, 0x00, 0x0006, $username, $passwd )；

unpack('Sint1/Cchar1/Sint2/Cchar2/',$lastmessage)；