Question

I am looking to create an auto incrementing unique string using PHP, containing [a-Z 0-9] starting at 2 chars long and growing when needed.

This is for a url shrinker so each string (or alias) will be saved in the database attached to a url.

Any insight would be greatly appreciated!

Answer 1

Here’s an implementation of an incr function which takes a string containing characters [0-9a-zA-Z] and increments it, pushing a 0 onto the front if required using the ‘carry-the-one’ method.

<?php

function incr($num) {
  $chars = '0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ';
  $parts = str_split((string)$num);

  $carry = 1;
  for ($i = count($parts) - 1; $i >= 0 && $carry; --$i) {
    $value = strpos($chars, $parts[$i]) + 1;
    if ($value >= strlen($chars)) {
      $value = 0;
      $carry = 1;
    } else {
      $carry = 0;
    }
    $parts[$i] = $chars[$value];
  }

  if ($carry)
    array_unshift($parts, $chars[0]);

  return implode($parts);
}

$num = '0';
for ($i = 0; $i < 1000; ++$i) {
  echo $num = incr($num), "\n";
}