Summary of Six Methods for Uploading and Renaming PHP Images

/*
 com_create_guid() is a function supported by the php5 version. For unsupported versions, you can define it yourself
*/
function guid(){
 if (function_exists('com_create_guid')){
 return com_create_guid();
 }else{
 mt_srand((double)microtime()*10000);//optional for php 4.2.0 and up.
 echo(mt_rand());
 $charid = strtoupper(md5(uniqid( rand(), true)));
 $hyphen = chr(45);// "-"
 $uuid = chr(123)// "{"
 .substr($charid, 0, 8).$hyphen
 .substr($charid, 8, 4).$hyphen
 .substr($charid,12, 4).$hyphen
 .substr($charid,16, 4).$hyphen
 .substr($charid,20 ,12)
 .chr(125);// "}"
 return $uuid;
 }
}

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 generated based on the input data. example:

$str = "Hello";
echo md5($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, which will cause great confusion; Disadvantages: 32-bit characters are too long; unique seed data needs to be provided; Usage: High concurrency, using seconds as the seed data, duplication will still occur.

/*
* Used in conjunction with the time() function, using the number of seconds from 1970 to the current time as the seed number
*/
$str=time();
echo md5($ str);
?>

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, which can 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. Detailed description: Definition: The uniqid() function generates a unique ID based on the current time in microseconds; Usage: uniqid(prefix,more_entropy); Note: 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.

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

The output 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 obfuscation, which can avoid back-referencing the original data; Disadvantages: Similar to md5, high concurrency, using seconds as the seed data, duplication will still occur. 3. Upgraded version plan 1. fast_uuid: returns 17 digits A bit like an incompletely customized version of uniqid(), the concept of "seed number starting time" that appears in this function 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 what we actually need is only It can be a value that can grow automatically. After the start time is customized, in addition to reducing the length, it can also play a role in confusion.

/*
* The parameter suffix_len specifies how many random digits are appended to the generated ID value. The default value is 3
* @param int suffix_len
* @return string
*/
function fast_uuid($suffix_len=3) {
 //! The starting time for calculating the seed number
 $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 2. time()+random number The use of random numbers has already appeared in the above example, in order to solve multiple requests that occur in one second. Two functions are provided:

function random($length) {
 $hash = '';
 $chars = 'ABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789abcdefghijklmnopqrstuvwxyz';
 $max = strlen($chars ) - 1;
 PHP_VERSION  for($i = 0; $i  $hash .= $chars[mt_rand(0, $max )];
 }
 return $hash;
}
function random2($length, $numeric = 0) {
 PHP_VERSION  $seed = base_convert(md5(print_r($_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  $hash .= $seed[mt_rand(0, $max)];
 }
 return $hash;
}
?>

four ,The final proposal Idea: userid+second+random number. Among them, "userid+second" is converted from decimal to 64, reducing the number of digits. illustrate: 1. userid: The maximum value of "ZZZZ" in hexadecimal is converted to decimal equal to "16777215", and the maximum value of "ZZZ" converted to decimal is equal to "262143"; 2. Seconds: Set your own time starting point. $less=time()-strtotime(’2012-4-21′) is converted to hexadecimal “1SpRe”, 5 digits $less=time()-strtotime(’2013-3-21′) is converted to hexadecimal “_jHY”, 4 digits 3. 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. 1 2 Next Page Last Page