Detailed explanation and examples of php pack() function

pack and unpack are really not easy to see in ordinary programs, but if you have used PHP to generate excel a long time ago, you will know it. The header of his excel is just packed. I recently used this thing again when trying to interact with C, so I had to take a look again. In fact, it was C who required me to have a Baotou. . . In fact, pure strings are also good. Why do you have to get a bun? Really confused...
There are introductions to pack and unpack in the manual, but they are all in English. . .

Any language with socket operation capabilities has a function specifically used for package assembly, and php is no exception! Do some binary operations with php. Recently, I used PHP to write a socket client to connect to a game server developed in C++ language. Server-side developers use a binary form to define the format of the protocol. The protocol format is as follows: Baot header (2bytes) + encryption (1byte) + command code (2bytes) + frame content 1. The content of the packet header is the length of the recorded frame content; 2. Encryption: 0 means no encryption, 1 means Encryption; 3. The command code is the server command identification symbol;
At first I didn’t know that PHP had pack to assemble binary packages, so I took a detour and asked server developers to help develop several memories using C language. The operation function returns the binary package according to the protocol rules, and then I compile these methods into a set of extension functions for PHP to use.


Back to the topic, this article introduces how to use the pack and unpack methods. The official PHP manual has too few examples to make it easy to understand, especially the use of formatting parameters.
Chinese explanation of the parameters of the excerpt:
pack/unpack template character character meaninga A byte string filled with empty spacesA A byte string filled with spaces
b A bit string, with bits in each byte The order is in ascending order B A bit string, the order of bits in each byte is in descending order c A signed char (8-bit integer) value
C An unsigned char (8-bit integer) value; about Unicode, see Ud A double-precision floating-point number in native format f A single-precision floating-point number in native format
h A hexadecimal string, low-order four bits first
H A hexadecimal string, high-order four digits first
i a signed integer value, native format
I an unsigned integer value, native format
l a signed long, always 32 bits
L an unsigned long, always 32 bits
n a 16-bit Short integer, "network" byte order (big endian)
N A 32-bit short integer, "network" byte order (big endian)
p A pointer to a null-terminated string
P A pointer to a fixed-length Pointer to string
q A signed quad (64-bit integer) value
Q An unsigned quad (64-bit integer) value
s A signed short integer value, always 16 bits
S An unsigned short integer Value, always 16 bits,
The byte order is related to the machine chip

u An unencoded string
U A Unicode character number
v A 16-bit short integer in "VAX" byte order (little end first)
V A 32-bit short integer in "VAX" byte order (little endian)
w A BER-compressed integer
x A null byte (one byte forward is ignored)
X Back up a byte
Z A Null-terminated (and null-padded) byte strings @ Pad absolute positions with null bytes string pack ( string $format [, mixed $args [, mixed $...]] )
Some rules:
1. Each letter can be followed by a number, which means count. If count is a *, it means everything else.
2. If you provide fewer parameters than $format requires, pack assumes that all missing values ​​are null. If you provide more parameters than $format requires, the extra parameters are ignored.
It will be easier to understand using examples below:



PHP code

1. About Pack:
3. The first part below packs the numeric value into bytes:
4. $out = pack("CCCC", 65, 66, ; , 66, 67, 68); # Same thing The following does the same thing for Unicode’s cyclic letters:
5. $foo = pack("U4", 0 x24b6, 0x24b7, 0x24b8 , 0x24b9);
7. The following does something similar, adding some empty space:
8. $out = pack("CCxxCC", 65, 66, 67 , 68);
9. $data = "010000020007";
10. unpack("Sint1/Cchar1/Sint2/Cchar2",$data );
12. ## array('int1'=>1, 'char1'=>'0','int2' => 2.'char2'=>7); $ lastact
13. = pack('SCSa32a32'
14. ,0x0040, 0x00, 0x0006, $username
15. , $passwd
16. ); unpack('Sint1/ Cchar1/Sint2/Cchar2/',$lastmessage); aspxMy above content comes from: http://blog.sina.com.cn/s/blog_3eba8f1c0100nq9r.html, I have now successfully used it. HeiheiThere are other reference materials:
http://bbs.phpchina.com/thread-104492-1-1.html
17. http://hi.baidu.com/chinetman/item/f78a71d847e7d638e2108fda The above introduces the detailed explanation and examples of the php pack() function, including the relevant content. I hope it will be helpful to friends who are interested in PHP tutorials.