generate random password/random string

[GumSlone]

easy way to generate random password

$length = 12; //password length
$password = substr(preg_replace('/\W/', '', md5(rand())), 0, $length); 

[Anshul]

/* If using PHP < 4.3.2, create our own session_regenerate_id() function */

if (!function_exists('session_regenerate_id')) {
    function make_seed() {
        list($usec, $sec) = explode(' ', microtime());
        return (float)$sec + ((float)$usec * 100000);
    }

    function php_combined_lcg() {
        mt_srand(make_seed());
        $tv = gettimeofday();
        $lcg['s1'] = $tv['sec'] ^ (~$tv['usec']);
        $lcg['s2'] = mt_rand();
        $q = (int) ($lcg['s1'] / 53668);
        $lcg['s1'] = (int) (40014 * ($lcg['s1'] - 53668 * $q) - 12211 * $q);
        if ($lcg['s1'] < 0) {
            $lcg['s1'] += 2147483563;
        }
        $q = (int) ($lcg['s2'] / 52774);
        $lcg['s2'] = (int) (40692 * ($lcg['s2'] - 52774 * $q) - 3791 * $q);
        if ($lcg['s2'] < 0) {
            $lcg['s2'] += 2147483399;
        }
        $z = (int) ($lcg['s1'] - $lcg['s2']);
        if ($z < 1) {
            $z += 2147483562;
        }
        return $z * 4.656613e-10;
    }

    function session_regenerate_id() {
        $tv = gettimeofday();
        $buf = sprintf("%.15s%ld%ld%0.8f", $_SERVER['REMOTE_ADDR'], $tv['sec'], $tv['usec'], php_combined_lcg() * 10);
        session_id(md5($buf));
        if (ini_get('session.use_cookies')) {
            setcookie(session_name(), session_id(), NULL, '/');
        }
        return TRUE;
    }
} 

Added after 7 minutes:

here are some others for generting random string

function generate_password($len = 10) {
    $result = '';
    $alpha  = 'abcdefghijklmnopqrstuvwxyz' .
          '0123456789' .
          'ABCDEFGHIJKLMNOPQRSTUVWXYZ';

    $size = strlen($alpha) - 1;
    $used = array();

    while ($len--) {
        $random  = mt_rand(0, $size);
        $char    = $alpha[$random];

        // No duplicate characters.
        if (in_array($char, $used, true)) {
            $len++;
            continue;
        }
        $used[]  = $char;
        $result .= $char;
    }
    return $result;
} 

function genGUID() {
    return md5(uniqid(mt_rand(), true));
}