How to generate unique identifiers in PHP

Identifier (IDentifier) ​​refers to a symbol used to identify an entity. It has different meanings in different application environments. This article mainly shares with you how to generate unique identifiers in PHP. I hope it can help you.

1. Applicable scenarios

Avoid duplication of file names

2. Conventional solution

2.1 guid

32 character hexadecimal system number.
Format: The format of the GUID is "xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx", where each x is a 32-digit hexadecimal number in the range of 0-9 or a-f. For example: 6F9619FF-8B86-D011-B42D-00C04FC964FF is a valid GUID value.

Advantages: Almost no repetition;
Disadvantages: It is still too long for renaming uploaded pictures.

Usage:

2.2 MD5

Like guid, it will output a 32-character hexadecimal number. The difference is that guid is randomly generated, and md5 needs to be based on the input data. generate.

< ?php$str = "Hello";echo md5($str);?>

Output:

8b1a9953c4611296a827abf8c47804d7

Advantages: The output value can be controlled based on the input seed data. If the seed data is regular and non-repeating, the data can be protected through md5, resulting in a lot of problems. Great confusion.

Disadvantages: 32-bit characters are too long; non-duplicate seed data needs to be provided; high concurrency, with seconds as the seed data, duplication will still occur.

Usage:

< ?php/*
*结合time()函数使用，以1970年到当前时间的秒数作为种子数。
*/$str=time();echo md5($str);?>

2.3 uniqid()

Returns a 13 or 23-digit string.
For our purposes, uniqid() is like an improved version of md5(), especially since we can use differential identifiers as string prefixes to reduce the chance of repeated naming.

For extreme situations such as non-high concurrency, it is recommended to use this function, which can already meet general needs.
Definition: The uniqid() function generates a unique ID based on the current time in microseconds.
Usage: uniqid(prefix,more_entropy)
Description: prefix can add a prefix to the output string. The example is as follows. When the more_entropy parameter is true, a 23-bit string will be output.

< ?phpvar_dump(uniqid());var_dump(uniqid("a"));
?>

The output result is:

string(13) “51734aa562254″ string(14) “a51734aa562257″

Advantages: 13-bit string length is an acceptable file naming length; prefixes can be added, and the result contains data confusion, which can avoid reverse inference of the original data.

Disadvantages: Similar to md5, high concurrency, using seconds as the seed data, duplication will still occur.

3. Upgraded version solution

3.1 fast_uuid: Returns 17 digits

It’s a bit like an incomplete customized version of uniqid(). The “seed number starts” that appears in this function The concept of "time" is very enlightening.
The default time used in time() and uniqid() is calculated from 1970, and the length is ten digits (1366512439). Using the "seed number starting time" can reduce this value, because we actually need Yes, it is just a value that can grow automatically.
After the starting time is customized, in addition to reducing the length, it can also play a role in confusion.

/*
* 参数 suffix_len指定 生成的 ID 值附加多少位随机数，默认值为 3。
* 感谢“Ivan Tan|谭俊青 DrinChing (at) Gmail.com”提供的算法。
* @param int suffix_len
* @return string*/function fast_uuid($suffix_len=3){ //! 计算种子数的开始时间 $being_timestamp = strtotime(’2013-3-21′); $time = explode(‘ ‘, microtime()); $id = ($time[1] – $being_timestamp) . sprintf(‘%06u’, substr($time[0], 2, 6)); if ($suffix_len > 0)
 { $id .= substr(sprintf(‘%010u’, mt_rand()), 0, $suffix_len);
 } return $id;
}

Output:

29832412631099013

3.2 time()+random number

The use of random numbers has already appeared in the above example, in order to solve the problem of multiple occurrences in one second ask. Two functions are provided as follows,

< ?phpfunction random($length) {
 $hash = ''; $chars = 'ABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789abcdefghijklmnopqrstuvwxyz'; $max = strlen($chars) - 1;
 PHP_VERSION < '4.2.0' && mt_srand((double)microtime() * 1000000); for($i = 0; $i < $length; $i++) { $hash .= $chars[mt_rand(0, $max)];
 } return $hash;
}function random2($length, $numeric = 0) {
 PHP_VERSION < '4.2.0' ? mt_srand((double)microtime() * 1000000) : mt_srand(); $seed = base_convert(md5(print_r($_SERVER, 1).microtime()), 16, $numeric ? 10 : 35); $seed = $numeric ? (str_replace('0', '', $seed).'012340567890') : ($seed.'zZ'.strtoupper($seed)); $hash = ''; $max = strlen($seed) - 1; for($i = 0; $i < $length; $i++) { $hash .= $seed[mt_rand(0, $max)];
 } return $hash;
}?>

4. Final solution

Idea: userid+second+random number. Among them, "userid+second" is converted from decimal to 64, reducing the number of digits;

Description:

1. userid: maximum value in 64 "ZZZZ" converted to decimal equals "16777215", and the maximum value of "ZZZ" converted to decimal equals "262143";

2. Seconds: Set your own time starting point.

$less=time()-strtotime(’2012-4-21′); 转换为64进制”1SpRe“，5位$less=time()-strtotime(’2013-3-21′); 转换为64进制”_jHY“；4位

1. Random number: Use random(3) to generate a 3-digit random number;

Final result:
4-digit userid+4-digit second+3-digit random number=11-digit string. Although the results look similar to uniqid(), the robustness is improved.

5. Summary

This article involves several methods that may be used to rename uploaded images. The key point is to use decimal to hexadecimal to reduce the string.

For example, the 17-digit number generated by fast_uuid is converted into a 64-digit number with only 7 characters;
The specific use can be used flexibly according to your own situation. I hope it will be helpful to everyone.

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