The pack of PHP's function

PHP does not attribute other categories of functions called Miscellaneous functions, also attributes PHP's core components

Pack ($format, arg+)//load data into a binary string

$format: Required to specify the format to use when wrapping data.
arg+: Optional, specify one or more parameters to be packaged

Possible values for $format parameters

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 the bit, machine byte order)

s-unsigned short (always the bit, machine byte order)

n-unsigned short (always the bit, big endian byte order)

v-unsigned short (always-on 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 the bit, machine byte order)

L-unsigned long (always the bit, machine byte order)

N-unsigned long (always the bit, big endian byte order)

V-unsigned long (always the 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

@-Nul-fill to absolute position

As an example:

Echo Pack ("S", +);    // If there is no data behind the format s or a specific number or *, then there can be only one argument later, if there is a specific number later, then the following argument is so many

P

Echo Pack　　("C3", 80,72,80); Indicates that there can be only 3 parameters at a later //PHP

$str NULL ;      for ($i= 0; $i<20; $i++)        {$strpack("S",mt_rand(80,128));    }     Echo $str ; // M{qxim^wslts_w[kvrsu

Echo Pack　　("c*", 80,72,80); // indicates that only 3 parameters can be followed//php

The pack of PHP's function