How to convert string to byte array in php

In PHP, strings are processed in the form of characters, and each character occupies a different number of bytes. When we need to convert a string into a byte array, it is usually for use in network communication, data transmission, data storage and other scenarios, because these scenarios require data to be processed in the form of byte arrays.

Conversion between strings and byte arrays in PHP requires the help of some functions. Below we will introduce these functions and their usage in detail.

1. strlen function

The first is the strlen function, which is used to obtain the length of a string, that is, the number of characters in the string, for example:

$str = "hello";
$len = strlen($str);
echo $len; // 输出 5

In the above example, $str is a string, which consists of 5 characters. Its length is obtained through the strlen function and the result is assigned to the $len variable, and finally the value of $len is output.

2. mb_strlen function

In PHP, by default, each character occupies one byte, but for complex character sets such as Chinese, one character may Multiple bytes are needed to represent, then you need to use the mb_strlen function to get the actual number of characters in the string, for example:

$str = "你好，世界！";
$len = mb_strlen($str, "utf-8");
echo $len; // 输出 7

In the above example, $str is a character containing Chinese characters If you use the strlen function to get the length of a string, you can only get 11. If you use the mb_strlen function, you need to specify the character set as utf-8 to correctly get the actual number of characters in the string.

3. str_split function

Next is the str_split function, which is used to split a string into an array of single characters, for example:

$str = "hello";
$arr = str_split($str);
print_r($arr); // 输出 Array ( [0] => h [1] => e [2] => l [3] => l [4] => o )

In In the above example, $str is a string, which is split into an array containing a single character through the str_split function, and the result is assigned to the $arr variable, and finally the print_r function is used to output the contents of $arr.

4. unpack function

The unpack function is a function that converts a binary string into an array. Its syntax is as follows:

array unpack ( string $format , string $data )

The $format parameter is For specifying the format of the data, the $data parameter is the binary string to be converted. The $format parameter is a string consisting of one or more format codes. Each format code is used to describe a data type and its corresponding number of bytes. Commonly used format codes and their corresponding data types are as follows:

• c - signed character
• C - unsigned character
• s - signed short integer
• S ​​- Unsigned short integer
• n - Unsigned short integer, network byte order
• i - Signed integer
• I - Unsigned integer
• l - signed long integer
• L - unsigned long integer
• N - unsigned long integer, network byte order

For example, if we need to convert a binary string containing integer data into an array, we can use the following code:

$data = "\x00\x12\x34\x56"; // 十六进制字符串
$arr = unpack("N", $data);
print_r($arr); // 输出 Array ( [1] => 305419896 )

In the above example, $data is a binary string containing a single integer data , convert it into an array containing one element through the unpack function, assign the result to the $arr variable, and finally use the print_r function to print the contents of $arr.

5. pack function

Contrary to the unpack function, the pack function is used to pack the array into a binary string. Its syntax is as follows:

string pack ( string $format , mixed $args1 [, mixed $args2 [, mixed $... ]] )

where The format code of $format is the same as that of the unpack function, which is used to specify the format of the packed data. Parameters such as $args1 and $args2 are the data to be packed, which can be one or more.

For example, if we need to pack an array into a binary string, we can use the following code:

$arr = array(305419896);
$data = pack("N", ...$arr);
echo bin2hex($data); // 输出 00123456

In the above example, $arr is an array containing an integer data , pack it into a binary string through the pack function, and assign the result to the $data variable. Finally, use the bin2hex function to convert $data into a hexadecimal string and output it.

To sum up, there are many ways to convert a string into a byte array in PHP, and you can choose the appropriate method according to the specific application scenario. No matter which method is used, you need to pay attention to issues such as character encoding and data format to get correct results.

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