PHP生成不重复标识符的方法
这篇文章主要介绍了PHP生成不重复标识符的方法,涉及时间函数time的md5转换,uniqid()函数及GUID的应用,非常具有实用价值,需要的朋友可以参考下
本文实例讲述了PHP生成不重复标识符的方法。分享给大家供大家参考。具体实现方法如下:
生成唯一不重复的标识我们主要是根据当前的一个时间time然后再转换在md5值,这样几乎是可以保证标签的唯一性,下面整理了一些关于PHP生成不重复标识符程序代码,感兴趣的朋友可以来看一下
PHP倒是自带了生成唯一id的函数:uniqid() ,它是基于当前时间微秒数的,用法如下:
复制代码 代码如下:
echo uniqid(); //13位的字符串
echo uniqid("php_"); //当然你可以加上前缀
echo uniqid("php_", TRUE); //如果第二个参数more_entropy为true则生成23位字符串
但是它生成的标识有可能不是唯一的,所以很多人会:
复制代码 代码如下:
//这是第一种简单的方法,当然用sha1()函数也可以。
echo md5(uniqid());
//第二种,利用时间戳的方法
echo md5(time() . mt_rand(1,1000000));
?>
例子:
复制代码 代码如下:
//生成唯一标识符
//sha1()函数, "安全散列算法(SHA1)"
function create_unique() {
$data = $_SERVER['HTTP_USER_AGENT'] . $_SERVER['REMOTE_ADDR']
.time() . rand();
return sha1($data);
//return md5(time().$data);
//return $data;
}
?>
例子如下:
复制代码 代码如下:
$newhash = create_unique();
echo $newhash;
?>
我看到很多人使用 md5() 函数,即使它并不完全意味着这个目的:
复制代码 代码如下:
// generate unique string
echo md5(time() . mt_rand(1,1000000));
There is actually a PHP function named uniqid() that is meant to be used for this.
// generate unique string
echo uniqid();
/* prints
4bd67c947233e
*/
// generate another unique string
echo uniqid();
/* prints
4bd67c9472340
*/
你可能会注意到,尽管字符串是唯一的,前几个字符却是类似的,这是因为生成的字符串与服务器时间相关。
但实际上也存在友好的一方面,由于每个新生成的 ID 会按字母顺序排列,这样排序就变得很简单。
为了减少重复的概率,你可以传递一个前缀,,或第二个参数来增加:
复制代码 代码如下:
// with prefix
echo uniqid('foo_');
/* prints
foo_4bd67d6cd8b8f
*/
// with more entropy
echo uniqid('',true);
/* prints
4bd67d6cd8b926.12135106
*/
// both
echo uniqid('bar_',true);
/* prints
bar_4bd67da367b650.43684647
*/
这个函数将产生比 md5() 更短的字符串,节省一些空间。
php生成全球唯一标识符(GUID)的方法
GUID在空间上和时间上具有唯一性,保证同一时间不同地方产生的数字不同。
世界上的任何两台计算机都不会生成重复的 GUID 值。
需要GUID的时候,可以完全由算法自动生成,不需要一个权威机构来管理。
GUID的长度固定,并且相对而言较短小,非常适合于排序、标识和存储。
复制代码 代码如下:
//php生成GUID
function getGuid() {
$charid = strtoupper(md5(uniqid(mt_rand(), true)));
$hyphen = chr(45);// "-"
$uuid = substr($charid, 0, 8).$hyphen
.substr($charid, 8, 4).$hyphen
.substr($charid,12, 4).$hyphen
.substr($charid,16, 4).$hyphen
.substr($charid,20,12);
return $uuid;
}
?>
希望本文所述对大家的php程序设计有所帮助。

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