PHP generate a unique string

Question

I have an ID column in a table which stores the row ID number (auto increment), For example 1, 2, 3. I want to generated a random and unique string which could contain only numbers, alphabets and dash (-) and underscore (_). The length of string should be 4-6, and it should be unique. Can someone help me how to generate? thanks.

possible duplicate of How to create a random string using PHP? — Roddy
– Roddy, Commented Jun 28, 2011 at 9:16
What have you tried to resolve the problem? Where are you stuck? — Nico Haase
– Nico Haase, Commented Sep 13, 2022 at 8:56

X10nD · Accepted Answer · 2011-06-28 05:38:44Z

2

Use this - base_convert(mt_rand(0x1D39D3E06400000, 0x41C21CB8E0FFFFFF), 10, 36), but check new value against db.

answered Jun 28, 2011 at 5:38

X10nD

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Marcus Olsson · Accepted Answer · 2012-08-06 12:34:22Z

0

function random_gen($length)
{
  $random= "";
  srand((double)microtime()*1000000);
  $char_list = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
  $char_list .= "abcdefghijklmnopqrstuvwxyz";
  $char_list .= "1234567890-_";
  // Add the special characters to $char_list if needed

  for($i = 0; $i < $length; $i++)
  {
    $random .= substr($char_list,(rand()%(strlen($char_list))), 1);
  }
  return $random;
}

$random_string = random_gen(6); //This will return a random 6 character string

Above function will generate the unique string

edited Aug 6, 2012 at 12:34

Marcus Olsson

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answered Jun 28, 2011 at 5:29

gmhk

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3 Comments

Zach Rattner Over a year ago

See my comment to the previous answer. You don't want to call strlen there, and you still have to guarantee uniqueness. This function only leverages probabilistic unlikeliness.

Alfred Over a year ago

My question is if this always generates an unique number of you try this long enough. Okay not more than the total number of permutations..

Zach Rattner Over a year ago

It is still possible (albeit unlikely) that this function will return the same value twice. You should check the database with a SELECT statement to make sure the string is unique.

Balanivash · Accepted Answer · 2011-06-28 05:30:22Z

-1

Try this

function genRandomString($length) {
   $characters = ’0123456789abcdefghijklmnopqrstuvwxyz-_’;
   $string = ”;    
   for ($p = 0; $p < $length; $p++) {
      $string .= $characters[mt_rand(0, strlen($characters))];
    }
   return $string;
}

Call the function with the length you want

answered Jun 28, 2011 at 5:30

Balanivash

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2 Comments

Zach Rattner Over a year ago

You're not going to want to call strlen every time you iterate over the for loop, since it's not going to change inside the loop. I'd recommend setting a variable to the output of strlen, and then use that inside the loop. Also, if you call this function inside of a do { ... } while (keyExists($String)); block, you can guarantee uniqueness. The keyExists function would have to do a SELECT statement to see if any rows exist with the given string.

Balanivash Over a year ago

ya.. strlen is going to be the same and a variable can be used for it. To guarantee uniqueness, storing and checking the db is absolutely necessary. Thanks :)

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