genrating random codes

[kante]

i wanted to generate a 8-letters code.

i tryed using
$value = rand(0, 10000000);

and
function NewUserCode($count = 8)
{
mt_srand((double)microtime()*1000000);
$key = "";
for ($i=0; $i<$count; $i++)
{
$c = mt_rand(0,2);
if ($c==0)
$key .= chr(mt_rand(65,90));
elseif ($c==1)
$key .= chr(mt_rand(97,122));
else
$key .= mt_rand(0,9);
}
return strtoupper(substr(uniqid($key), 0, $count));
}

but on run time i catch that these php random functions doesn't generate a so casual code... in fact testing with this code:

$max =100000000000;
$randoms = array();
for ($i=0;$i<$max;$i++){
$value = NewUserCode();
if(in_array($value,$randoms))
die("Found after $i times the value $value");
else
$randoms[$i] = $value;
}
printf("finished");

it too often generate the same code...

what do u suggest me?

Thak you

[laserlight]

Do not seed the pseudorandom number generator more than once in a script.
In fact, since PHP 4.2.0, you dont need to explicitly seed the pseudorandom number generator.

There's not much point in using uniqid() here, unless you want to use:

function newUserCode($count = 8)
{
	return substr(uniqid(mt_rand(), true), 0, $count);
}

Using your original idea:

function newUserCode($count = 8)
{
	$key = "";
	for ($i = 0; $i < $count; $i++)
	{
		switch (mt_rand(0, 2))
		{
		case 0:
			$key .= chr(mt_rand(65, 90));
			break;
		case 1:
			$key .= chr(mt_rand(97, 122));
			break;
		case 2:
			$key .= mt_rand(0, 9);
		}
	}
	return $key;
}

[drawmack]

To make the codes unique you'll have to check if the generated code has already been generated.

You can accomplish this a couple of ways depending on your implementation.

If you're generating a bunch in a single script then do something like this:

<?php
//testing code remove for production
$num_codes = 10000;
$num_tries = 20;

echo 'generating codes';
flush();

$start_time = getmicrotime();
$codes = gen_codes($num_codes,$num_tries);
$end_time = getmicrotime();

$run_time = $end_time - $start_time;

echo 'Generated ' . $num_codes . ' in ' . $run_time . ' seconds<br>'; 
foreach(array_keys($codes) as $code) {
    echo $code . ': ' . $codes[$code] . "<br>\n";
} //end foreach
//end testing code

//this function generates a series of codes with no repeats.
//it will exit and return the list when num_codes codes have
//been generated or max_tries duplicates are generated for a
//single code 
/*array*/ function gen_codes($num_codes=0,$max_tries = 100) {
    $codes = array();
    $i = 0;
    while(count($codes) < $num_codes && $i < $max_tries) {
        //generate a random code
        $code = gen_code(8);
        //add it to codes if it's not already there
        //if it is already there then increment the 
        //repeat counter
        if(!in_array($code,$codes)) {
            $codes[] = $code /*testing code*/ . ' - ' . $i /*end testing code*/;
            $i = 0;
        } else {
            $i++;
        } //end if

    //testing code remove for production
    if(count($codes)%100 == 0) {
        echo '.';
        flush();
    }
    //end testing code
} //end while

//testing code remove for production
echo '<br>';
//end testing code

return $codes;
} //end gen_codes

//this function will generate a single alpha
//numeric code that is len characters long
/*string*/ function gen_code($len = 6) {
    $code = '';
    for($i=0;$i<$len;$i++) {
        switch (mt_rand(0,2)) {
            case 0:
               $code .= chr(mt_rand(65,90));
               break;
            case 1:
               $code .= chr(mt_rand(97,122));
               break;
            case 2:
                $code .= mt_rand(0,9);
        } //end switch
    } //end for 
    return $code; 
} //end gen_code

//testing code remove for production
function getmicrotime() 
{ 
   list($usec, $sec) = explode(" ", microtime()); 
   return ((float)$usec + (float)$sec); 
} 
//end testing code
?>

On my server this code generated 10000 codes in 29.313146829605 seconds

Now if you're only generating one code per run then you'll have to save the already generated list to a file and check if your new code is in that file with something like this.

<?php
//testing code remove for production
$file_name = '../../data_files/unique_codes.txt';

echo 'generating code<br>';
flush();

$code = gen_unique_code($file_name);

if($code != 0) {echo $code . '<br>';}
else {echo 'Could not generate unique code<br>';}
//end testing code

//this function generates a code that does not already exist in the file
//file pointed to by file_name. If max_tries repeated codes occur then 
//the function returns zero.
/*string*/ function gen_unique_code($file_name = 'unique_codes.txt',$max_tries = 10000) {
    //read the already generated codes into an array;
    if(file_exists($file_name)) {$codes = file($file_name);}
    else {
        $handle = fopen($file_name,'w');
        fclose($handle);
        chmod($file_name,0777);
        $codes = array();
    } //end if

//remove the line returns from the codes file
for($i=0;$i<count($codes);$i++) {
    $codes[$i] = rtrim($codes[$i]);
} //end for

$i = 0;
$code = '';
while($i < $max_tries && $code == '') {
    //generate a random code
    $code = gen_code(8);
    //add it to codes if it's not already there
    //if it is already there then increment the 
    //repeat counter
    if(in_array($code,$codes)) {
        $i++;
        $code == '';
    } //end if
} //end while

if($i == $max_tries) {return 0;}

//write the new code to the file
$handle = fopen($file_name,'a') or die('could not open ' . $file_name . ' for writting');
fwrite($handle,$code . "\n");
fclose($handle);

return $code;
} //end gen_codes

//this function will generate a single alpha
//numeric code that is len characters long
/*string*/ function gen_code($len = 6) {
    $code = '';
    for($i=0;$i<$len;$i++) {
        switch (mt_rand(0,2)) {
            case 0:
               $code .= chr(mt_rand(65,90));
               break;
            case 1:
               $code .= chr(mt_rand(97,122));
               break;
            case 2:
                $code .= mt_rand(0,9);
        } //end switch
    } //end for 
    return $code; 
} //end gen_code
?>