如何正确运用PHP随机数类

PHP随机数类代码示例：

1. < ?php
2. class getRandstrClass{
3. function getCode ($length = 32, $mode = 0) {
4. switch ($mode) {
5. case '1':
6. $str = '1234567890';
7. break;
8. case '2':
9. $str = 'abcdefghijklmnopqrstuvwxyz';
10. break;
11. case '3':
12. $str = 'ABCDEFGHIJKLMNOPQRSTUVWXYZ';
13. break;
14. case '4':
15. $str = 'ABCDEFGHIJKLMNOPQRSTUVWXYZa
    bcdefghijklmnopqrstuvwxyz';break;
16. case '5':
17. $str = 'ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890';
18. break;
19. case '6':
20. $str = 'abcdefghijklmnopqrstuvwxyz1234567890';
21. break;
22. default:
23. $str = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcde
    fghijklmnopqrstuvwxyz1234567890';
24. break;
25. }
26. $randString = '';
27. $len = strlen($str)-1;
28. for($i = 0;$i < $length;$i ++){
29. $num = mt_rand(0, $len);
30. $randString .= $str[$num];
31. }
32. return $randString ;
33. }
34. }
35. /* 使用方法
36. $code = new getRandstrClass();
37. $length = 4;
38. $mode = 0;
39. $str = $code->getCode($length, $mode);
40. echo $str;
41. $code = NULL;
42. */
43. ?>

以上这段代码就是PHP随机数类的具体使用方法。