Detailed introduction to 6 solutions to renaming uploaded images based on PHP_PHP Tutorial

1. Applicable scenarios: You cannot use the self-increasing number returned from the database to rename uploaded images.

This is determined by the process of uploading images or files.
The general image upload process is to first upload the image to the server, rename it, and then insert it into the database.
That is to say, the self-increasing ID that is very easy to obtain in the database cannot be used to rename uploaded pictures to avoid duplication of file names.
Instead, the maximum ID plus 1 is obtained from the database. , increases the number of database connections, and is not suitable for situations with high concurrency and huge data volume;

2. Conventional plan:

1, guid: 32-character hexadecimal number.
Format: The GUID is in the format "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:

Copy code The code is as follows:

/*
com_create_guid() is php5 The functions supported by the version can be defined by yourself for unsupported versions;
*/
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). ,16, 4).$hyphen
.substr($charid,20,12)
.chr(125);// "}"
return $uuid;
}
}

2, MD5:
will output a 32-character hexadecimal number just like guid. The difference is that guid is randomly generated, and md5 needs to be generated based on the input data.
Example,

Copy code The code is as follows:

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

output,

Copy code The code is as follows ; protection, creating great confusion. Disadvantages: 32-bit characters are too long; non-duplicate seed data needs to be provided;

Usage: High concurrency, with seconds as the seed data, duplication will still occur.

Copy code

The code is as follows:

/** combined with the time() function Use the number of seconds from 1970 to the current time as the seed number. */$str=time();

echo md5($str);

?>


3, uniqid(): return 13 or 23 Bit 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.
Details,
Definition: The uniqid() function generates a unique ID based on the current time in microseconds.
Usage: uniqid(prefix,more_entropy)

Explanation: 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.



Copy code

The code is as follows:

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

The output result is:

Copy code The code is as follows:

string(13) "51734aa562254" string(14) "a51734aa562257"

Advantages: 13-digit string length is an acceptable file naming length; prefixes can be added, and the result contains data confusion, 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 a 17-digit number.
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 start time" can reduce this value, because we actually need Yes, it is just a value that can grow automatically.
After customizing the starting time, in addition to reducing the length, it can also play a role in confusion.

Copy code The code is as follows:

/*
* The parameter suffix_len specifies how many random digits are appended to the generated ID value , the default value is 3.
* Thanks to "Ivan Tan | Tan Junqing DrinChing (at) Gmail.com" for providing the algorithm.
* @param int suffix_len
* @return string
*/
function fast_uuid($suffix_len=3){
                                                                                                                                                                        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,

Copy code The code is as follows:

29832412631099013

2, time()+random number:
In the above example, random numbers have been used to solve multiple requests that occur in one second. Provide two functions as follows,

Copy code The code is as follows:

function 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;
}
?>

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

Description:

1, userid: The maximum value of "ZZZZ" converted into decimal is equal to "16777215", and the maximum value of "ZZZ" converted into decimal is equal to "262143";
2, seconds: set yourself the starting point of time.
$less=time()-strtotime('2012-4-21'); Convert to hexadecimal "1SpRe", 5 digits
$less=time()-strtotime('2013-3-21 '); Convert 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.

Five, decimal to hexadecimal conversion algorithm:

1, Algorithm 1:

Copy code The code is as follows:

View Code

const KeyCode = '0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ_$';

    /**
* Convert a 64-digit string to a decimal string
* @param $m string 64-digit string
* @param $len integer Returns the length of the string , if the length is not enough, fill it with 0, 0 means no padding
* @return string
* @author 马野
*/
    function hex64to10($m, $len = 0) {
        $m = (string)$m;
        $hex2 = '';
        $Code = KeyCode;
        for($i = 0, $l = strlen($Code); $i < $l; $i++) {
            $KeyCode[] = $Code[$i];
        }
        $KeyCode = array_flip($KeyCode);

        for($i = 0, $l = strlen($m); $i < $l; $i++) {
            $one = $m[$i];
            $hex2 .= str_pad(decbin($KeyCode[$one]), 6, '0', STR_PAD_LEFT);
        }
        $return = bindec($hex2);

        if($len) {
            $clen = strlen($return);
            if($clen >= $len) {
                return $return;
            }
            else {
                return str_pad($return, $len, '0', STR_PAD_LEFT);
            }
        }
        return $return;
    }

    /**
* Convert the decimal numeric string to a 64-digit numeric string
* @param $m string Decimal numeric string
* @param $len integer Returns the string length , if the length is not enough, fill it with 0, 0 means no padding
* @return string
* @author 马野
*/
    function hex10to64($m, $len = 0) {
        $KeyCode = KeyCode;
        $hex2 = decbin($m);
        $hex2 = str_rsplit($hex2, 6);
        $hex64 = array();
        foreach($hex2 as $one) {
            $t = bindec($one);
            $hex64[] = $KeyCode[$t];
        }
        $return = preg_replace('/^0*/', '', implode('', $hex64));
        if($len) {
            $clen = strlen($return);
            if($clen >= $len) {
                return $return;
            }
            else {
                return str_pad($return, $len, '0', STR_PAD_LEFT);
            }
        }
        return $return;
    }

    /**
* Convert hexadecimal number string to hexadecimal number string
* @param $m string Hexadecimal number string
* @param $len integer Returns the string length , if the length is not enough, fill it with 0, 0 means no padding
* @return string
* @author 马野
*/
    function hex16to64($m, $len = 0) {
        $KeyCode = KeyCode;
        $hex2 = array();
        for($i = 0, $j = strlen($m); $i < $j; ++$i) {
            $hex2[] = str_pad(base_convert($m[$i], 16, 2), 4, '0', STR_PAD_LEFT);
        }
        $hex2 = implode('', $hex2);
        $hex2 = str_rsplit($hex2, 6);
        foreach($hex2 as $one) {
            $hex64[] = $KeyCode[bindec($one)];
        }
        $return = preg_replace('/^0*/', '', implode('', $hex64));
        if($len) {
            $clen = strlen($return);
            if($clen >= $len) {
                return $return;
            }
            else {
                return str_pad($return, $len, '0', STR_PAD_LEFT);
            }
        }
        return $return;
    }

    /**
* The function is similar to the PHP native function str_split, except that the cutting starts from the end
* @param $str string The string to be cut
* @param $len integer The length of each string
* @return array
* @author 马野
*/
    function str_rsplit($str, $len = 1) {
        if($str == null || $str == false || $str == '') return false;
        $strlen = strlen($str);
        if($strlen <= $len) return array($str);
        $headlen = $strlen % $len;
        if($headlen == 0) {
            return str_split($str, $len);
        }
        $return = array(substr($str, 0, $headlen));
        return array_merge($return, str_split(substr($str, $headlen), $len));
    }

$a=idate("U");
echo "rn
e:" . hex10to64($a);
echo "rn
e:" . hex64to10(hex10to64($a));

2，算法2：

复制代码 代码如下:

View Code

function dec2s4($dec) { 
    $base = '0123456789_$abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ'; 
    $result = ''; 

    do { 
        $result = $base[$dec % 64] . $result; 
        $dec = intval($dec / 64); 
    } while ($dec != 0); 

    return $result; 
} 

function  s42dec($sixty_four) { 
    $base_map = array ( '0' => 0,    '1' => 1,    '2' => 2,    '3' => 3,    '4' => 4,    '5' => 5,    '6' => 6,    '7' => 7,    '8' => 8,    '9' => 9,    '_' => 10,    '$' => 11,    'a' => 12,    'b' => 13,    'c' => 14,    'd' => 15,    'e' => 16,    'f' => 17,    'g' => 18,    'h' => 19,    'i' => 20,    'j' => 21,    'k' => 22,    'l' => 23,    'm' => 24,    'n' => 25,    'o' => 26,    'p' => 27,    'q' => 28,    'r' => 29,    's' => 30,    't' => 31,    'u' => 32,    'v' => 33,    'w' => 34,    'x' => 35,    'y' => 36,    'z' => 37,    'A' => 38,    'B' => 39,    'C' => 40,    'D' => 41,    'E' => 42,    'F' => 43,    'G' => 44,    'H' => 45,    'I' => 46,    'J' => 47,    'K' => 48,    'L' => 49,    'M' => 50,    'N' => 51,    'O' => 52,    'P' => 53,    'Q' => 54,    'R' => 55,    'S' => 56,    'T' => 57,    'U' => 58,    'V' => 59,    'W' => 60,    'X' => 61,    'Y' => 62,    'Z' => 63,  ); 
    $result = 0; 
    $len = strlen($sixty_four); 

    for ($n = 0; $n < $len; $n++) { 
        $result *= 64; 
        $result += $base_map[$sixty_four{$n}]; 
    } 

    return $result; 
} 

$a=idate("U");
var_dump(dec2s4($a)); 
var_dump(s42dec(dec2s4($a)));

3，算法效率测试：

复制代码 代码如下:

View Code

$strarr = array();
$time1 = microtime(true);
for($i = 0; $i < 10000; ++$i) {
     $str = idate("U")+$i;
     $strarr[] = "{$i}->$strrn
";
 }
 $time2 = microtime(true);
 $time3 = $time2 - $time1;

 $time1 = microtime(true);
 for($i = 0; $i < 10000; ++$i) {
     $str = dec2s4(idate("U")+$i);
    $strarr[] = "{$i}->$strrn
";
}
$time2 = microtime(true);
echo "rn
运行10000次用时（秒）：" . ($time2 - $time1 - $time3);

4, test results
Algorithm 1: 0.1687250137329
Algorithm 2: 0.044965028762817
5, conclusion: Although Algorithm 1 is less efficient, it can convert the hexadecimal generated by md5 into hexadecimal. , can be used to shorten strings in environments where md5 must be used.

6. 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 hexadecimal with only 7 characters;
The specific use can be used flexibly according to your own situation. I hope it will be helpful to everyone.

Reference:

1, GUID Baidu Encyclopedia: http://baike.baidu.com/view/185358.htm
2, com_create_guid() official guide: http://www.php.net/manual/zh/function .com-create-guid.php
3, MD5() function description: http://www.w3school.com.cn/php/func_string_md5.asp
4, time() function description: http:/ /www.w3school.com.cn/php/func_date_time.asp
5, uniqid() function description: http://www.w3school.com.cn/php/func_misc_uniqid.asp

http://www.bkjia.com/PHPjc/326899.htmlwww.bkjia.comtruehttp: //www.bkjia.com/PHPjc/326899.htmlTechArticle1. Applicable scenario: You cannot use the self-increasing number returned from the database to rename the uploaded image. This is determined by the process of uploading images or files. General image upload processing process...