At work, I also learned that Pack,unpack,ord is powerful for binary byte processing. Let me introduce them to you. In our work, there is not much estimation of their use. I am in a recent job, because the communication needs to use the binary stream, and then the interface is received in PHP. At that time, a lot of information was consulted. Because they are really less used, they are seldom used by friends in their work. At work, I also learned that Pack,unpack,ord is powerful for binary byte processing. Let me introduce them to you.
Description of the pack function:This function is used to compress the data into a string that is packed into place.
Syntax:Pack (format,args+)
parameter Description
Format required. Specifies the format to use when wrapping the data.
Args+ is optional. Specifies one or more parameters that are packaged.
Character description
A fills the string blank with a NULL character
A fills the string blanks with space characters (spaces)
H 16 string, low in front
H 16 string, high in front
C with number characters
C No number character
S has a short integer (16 bits, depending on the computer's bit order)
S no-number short integer (16 bits, depending on the computer's bit order)
n unsigned short integers (16-bit, high-order in the back)
V Short Integer (16 bits, low in the back order)
I number integers (depending on the computer's order and range)
I no-number integers (depending on the computer's order and range)
L number Long Integer (32 bits, depending on the computer's bit order)
L unsigned long integers (32 bits, depending on the computer's bit order)
N unsigned short integers (32-bit, high-order in the back)
V short Integer (32 bits, low in the back order)
F Single precision floating point number (depending on the range of the computer)
D-times accurate floating point number (depending on the computer's range)
X vacancy
X Rewind One
@ Fill in NULL characters to absolute position
Unpack function Description:This function is used to extract the data of a bit string
Syntax:Unpack (format,args+)
parameter Description
Format required. Specifies the format to use when wrapping the data.
Args+ is optional. Specifies one or more parameters that are packaged.
The parameters are the same as the pack.
Ord function Description:Returns the Acill code value of the corresponding character
Syntax:Ord ($character);
Example Description:
Copy CodeThe code is as follows:
A character
$str = (Pack ("A *", "China"));
echo $str, "=", strlen ($STR), "Byte \ n";
Getascill ($STR);
H character
$str = (Pack ("h*", "Fffe"));
echo $str, "=", strlen ($STR), "Byte \ n";
Getascill ($STR);
C character
$str = (Pack ("c*", "55", "56", "57"));
echo $str, "=", strlen ($STR), "Byte \ n";
Getascill ($STR);
I-character short-shaped 32-bit 4-byte 64-bit 8-byte
$str = (Pack ("I", "100"));
echo $str, "=", strlen ($STR), "Byte \ n";
Getascill ($STR);
s character short shaping 2 bytes
$str = (Pack ("s", "100"));
echo $str, "=", strlen ($STR), "Byte \ n";
Getascill ($STR);
L character-length shaping 4 bytes
$str = (Pack ("L", "100"));
echo $str, "=", strlen ($STR), "Byte \ n";
Getascill ($STR);
F-character single-precision floating-point 4 bytes
$str = (Pack ("F", "100"));
echo $str, "=", strlen ($STR), "Byte \ n";
Getascill ($STR);
D-character double-precision floating-point 8 bytes
$str = (Pack ("D", "100"));
echo $str, "=", strlen ($STR), "Byte \ n";
Getascill ($STR);
function Getascill ($STR)
{
$arr =str_split ($STR);
foreach ($arr as $v)
{
echo $v, "=", Ord ($v), "\ n";
}
echo "=============\r\n\r\n";
}
?>
With the above example, we can see that the same string, stored in a different format, consumes a different number of bytes. It can also be seen here that saving characters in different formats can save space for storage. and start the unreadable encryption effect. Suddenly think of a bit, Design database field type problems, if a field is just: 10-bit length integer type. We set it to reshape: 256*256*256*256 is 4 bytes, if set to 10 length string. That accounts for 10 bytes. The whole digestive space is twice times the size. Setting the correct character type is a great help in improving database performance. Oh, a little off-topic ...
A case analysis of PHP processing byte code communication
just said pack function: space-saving, encrypted format
Here are 2 examples to illustrate, interface development requirements:
parameter Description
User name 20 bytes, character type
Password 10 bytes, character type
Age 1 Bytes, no character char type
Date of birth 4 bytes, integer (19800101)
Mailbox 50 Bytes, string
Between fields: "\" split
A, pack packaging
Copy CodeThe code is as follows:
$code =array (
"Username" =>array ("A20", "Zhang San Adfb12"),
"Pass" =>array ("A10", "asdf* #1"),
"Age" =>array ("C", "23"),
"Birthday" =>array ("I", "19900101"),
"Email" =>array ("A50", "zhangsan@163.com"));
$stream =join ("n", Packbyarr ($code));
Echo $stream, strlen ($stream);
File_put_contents ("C:/1.txt", $stream); Save the stream for easy reading below.
function Packbyarr ($arr) {
$ATARR =array ();
foreach ($arr as $k = = $v) {
$ATARR []=pack ($v [0], $v [1]);
}
return $ATARR;
}
function Getascill ($STR) {
$arr =str_split ($STR);
foreach ($arr as $v) {
echo $v, "=", Ord ($v), "\ n";
}
}
?>
The entire length is 89 bytes, because it is split with "\". With the above output, some string output can be read, the others have become garbled. This is what I said can be kept secret effect reason.
B, unpack unpacking
The unpacking needs to be read in a packaged manner, the length of the read, what type to read, and the same as the packing rules.
Copy CodeThe code is as follows:
$code =array (
"Username" =>array ("A20"),
"Pass" =>array ("A10"),
"Age" =>array ("C"),
"Birthday" =>array ("I"),
"Email" =>array ("A50"));
$stream =file_get_contents ("C:/1.txt");
Var_dump (Packbyarr ($stream, $code));
function Packbyarr ($STR, $code) {
$ARR =explode ("n", $str);
$ATARR =array ();
$i = 0;
foreach ($code as $k = = $v) {
$ATARR [$k]=unpack ($v [0], $ARR [$i]);
$i + +;
}
return $ATARR;
}
?>
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