基于php 随机数的深入理解
php mt_srand 播下一个更好的随机数发生器种子
mt_srand
(PHP 3 >= 3.0.6, PHP 4, PHP 5)
mt_srand -- 播下一个更好的随机数发生器种子
说明
复制代码 代码如下:
void mt_srand ( int seed )
用 seed 来给随机数发生器播种。从 PHP 4.2.0 版开始，seed 参数变为可选项，当该项为空时，会被设为随时数。
例子 1. mt_srand() 范例
复制代码 代码如下:
Code highlighting produced by Actipro CodeHighlighter (freeware)http://www.CodeHighlighter.com/-->// seed with microseconds
function make_seed()
{
list($usec, $sec) = explode(' ', microtime());
return (float) $sec + ((float) $usec * 100000);
}
mt_srand(make_seed());
$randval = mt_rand();
?>
注: 自 PHP 4.2.0 起，不再需要用 srand() 或 mt_srand() 函数给随机数发生器播种，现已自动完成。
参见 mt_rand()，mt_getrandmax() 和 srand()。
PHP mt_rand() 函数
定义和用法
mt_rand() 使用 Mersenne Twister 算法返回随机整数。
语法
复制代码 代码如下:
mt_rand(min,max)
说明
如果没有提供可选参数 min 和 max，mt_rand() 返回 0 到 RAND_MAX 之间的伪随机数。例如想要 5 到 15（包括 5 和 15）之间的随机数，用 mt_rand(5, 15)。
很多老的 libc 的随机数发生器具有一些不确定和未知的特性而且很慢。PHP 的 rand() 函数默认使用 libc 随机数发生器。mt_rand() 函数是非正式用来替换它的。该函数用了 Mersenne Twister 中已知的特性作为随机数发生器，它可以产生随机数值的平均速度比 libc 提供的 rand() 快四倍。
提示和注释
注释：自 PHP 4.2.0 起，不再需要用 srand() 或 mt_srand() 函数给随机数发生器播种，现在已自动完成。
注释：在 3.0.7 之前的版本中，max 的含义是 range 。要在这些版本中得到和上例相同 5 到 15 的随机数，简短的例子是 mt_rand (5, 11)。
例子
在本例中，我们会返回一些随机数：
复制代码 代码如下:
echo(mt_rand());
echo(mt_rand(10,100));
?>
输出类似：
3150906288
513289678
35
注意：上面这个函数给出的随机整数，数字之外的字符是不会出来的，若想其他字符产生，就需另自定义方法，如下所示：
复制代码 代码如下:
/*
* $length:随机数字符串的长度
* $type:产生随机数的类型
* */
function random($length, $type = "") {
$chars = !$type ? "ABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789abcdefghijklmnopqrstuvwxyz" : "0123456789abcdef";
$max = strlen($chars) - 1;
mt_srand((double)microtime() * 1000000);
for($i = 0; $i $string .= $chars[mt_rand(0, $max)];
}
return $string;
}
$var=random(32,'haha');
echo($var);
?>
输出:
fe61e294e5f46437cb3a92b92643ead6
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