Question

For generating random string i written code like this But if the function is called with a negative value, or zero, or 1 million it will create lot of problems. So please suggest me better code.

/*
* The following function is for generating a random string value.
* @param unknown_type $length
* @return string $randString
*/
function generateRandomString( $length ) {
    $randString = "";
    srand();
    $characters = "abcdefghijklmnopqrstuvwxyz1234567890";
    /*
    *   build string of random characters
    */ 
    while( strlen( $randString ) < $length ) {
        $randString .= substr( $characters, rand() % (strlen( $characters )),1 );
    }
return $randString;
}

Answer 1

To stop the negative number or zero passed as an argument as being a problem, you could use max(1, $length). Alternatively, check for < 1 and throw an exception or return FALSE.

So please suggest me better code.

Here are some suggestions for your code…

function generateRandomString( $length ) {
    $chars = array_merge(range('a', 'z'), range(0, 9));
    shuffle($chars);
    return implode(array_slice($chars, 0, $length));
}

CodePad.

Note that this won’t ever have the same character twice in the resulting string.

If you do desire that, you could use something like…

function generateRandomString( $length ) {
    $chars = array_merge(range('a', 'z'), range(0, 9));

    return array_reduce(array_rand($chars, $length), function($str, $key) use ($chars) { 
        return $str.= $chars[$key];
    }, ''); 

}

CodePad.

…or slightly different…

function generateRandomString( $length ) {
    $chars = array_merge(range('a', 'z'), range(0, 9));

    return implode(array_map(function($key) use ($chars) { 
        return $chars[$key];
    }, array_rand($chars, $length)));   

}

CodePad.