PHP最强大的随机字符串生成函数

/**
 * 随机字符
 * @param number $length 长度
 * @param string $type 类型
 * @param number $convert 转换大小写
 * @return string
 */
function random($length=6, $type='string', $convert=0){
 $config = array(
 'number'=>'12345670',
 'letter'=>'abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ',
 'string'=>'abcdefghjkmnpqrstuvwxyzABCDEFGHJKMNPQRSTUVWXYZ234567',
 'all'=>'abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ12345670'
 );
 
 if(!isset($config[$type])) $type = 'string';
 $string = $config[$type];
 
 $code = '';
 $strlen = strlen($string) -1;
 for($i = 0; $i < $length; $i++){
 $code .= $string{mt_rand(0, $strlen)};
 }
 if(!empty($convert)){
 $code = ($convert > 0)? strtoupper($code) : strtolower($code);
 }
 return $code;
}