php 랜덤 문자 만들기

 function GenerateString($length)  
{  
    $characters  = "0123456789";  
    $characters .= "abcdefghijklmnopqrstuvwxyz";  
    $characters .= "ABCDEFGHIJKLMNOPQRSTUVWXYZ";  
    $characters .= "_";  
      
    $string_generated = "";  
      
    $nmr_loops = $length;  
    while ($nmr_loops--)  
    {  
        $string_generated .= $characters[mt_rand(0, strlen($characters) - 1)];  
    }  
      
    return $string_generated;  
}  


echo GenerateString(15);