rand()

(PHP 4, PHP 5, PHP 7)

产生一个随机整数

说明

如果没有提供可选参数$min和$max，rand()返回 0 到getrandmax()之间的伪随机整数。例如想要 5 到 15（包括 5 和 15）之间的随机数，用rand(5, 15)。

Note:在某些平台下（例如 Windows）getrandmax()只有 32767。如果需要的范围大于 32767，那么指定$min和$max参数就可以生成更大的数了，或者考虑用mt_rand()来替代之。

参数

返回的最低值（默认：0）

返回的最高值（默认：getrandmax()）

返回值

A pseudo random value between$min(or 0)and$max(orgetrandmax(), inclusive).

更新日志

范例

Example #1rand()例子

以上例程的输出类似于：

7771
22264
11

参见

• srand() 播下随机数发生器种子
• getrandmax() 显示随机数最大的可能值
• mt_rand() 生成更好的随机数

quick way to generate randomish numbers and simple strings.
no messing around with functions, so you can just pop the line into the middle of your existing code.
not the most perfect for sure, but ok for plenty of situations...

hope someone finds it useful for somthing.
regards,
deeeeeen alxndr0u

I also enjoy making one-liners.
Here's a non-regular expression approach. It generates a random 32 character string consisting of, by default, only A-Z, a-z, and 0-9, but you can change the value of $a for other characters. The random string will be in variable $s after this line.

If you don't want the same character to appear beside itself, use this:

For those of you who want both as a function, use this:

string $c is the string of characters to use.
integer $l is how long you want the string to be.
boolean $u is whether or not a character can appear beside itself.
Examples:
rand_chars("ABCEDFG", 10) == GABGFFGCDA
rand_chars("ABCEDFG", 10, TRUE) == CBGFAEDFEC

Here's an interesting note about the inferiority of the rand() function. Try, for example, the following code...

which produces something similar to the following output (on my windows box, where RAND_MAX is 32768):
Array
(
  [0] => 31
  [1] => 0
  [2] => 0
  [3] => 31
  [4] => 0
  [5] => 0
  [6] => 30
  [7] => 0
  [8] => 0
  [9] => 31
  [10] => 0
)
Within this range only multiples of 3 are being selected. Also note that values that are filled are always 30 or 31 (no other values! really!) 
Now replace rand() with mt_rand() and see the difference...
Array
(
  [0] => 8
  [1] => 8
  [2] => 14
  [3] => 16
  [4] => 9
  [5] => 11
  [6] => 8
  [7] => 9
  [8] => 7
  [9] => 7
  [10] => 9
)
Much more randomly distributed!
Conclusion: mt_rand() is not just faster, it is a far superior algorithm.

Since many people (myself included) come to this page looking for a way to do a random string, I present a way that uses arrays and shuffle() instead of rand(). This also has the effect of not repeating any characters in the value set.
  $arr = str_split('ABCDEFGHIJKLMNOP'); // get all the characters into an array
  shuffle($arr); // randomize the array
  $arr = array_slice($arr, 0, 6); // get the first six (random) characters out
  $str = implode('', $arr); // smush them back into a string

A small comment on phpdev-dunnbypauls conclusion that rand() only generates numbers that are a multiply of 3. 

Since, 100000/32768=3.05 you get multiples of 3. The random integer will be multiplied by 3.05 to fit between 0 and 100000. rand() works fine, if you don't ask for bigger numbers then RAND_MAX.

If you are looking for generate a random expression, like password with alphanumeric or any other character, use this function: 

I agree with Sebmil (http://php.net/manual/en/function.array-rand.php#105265) that "array_rand()" produces weird and very uneven random distribution (as of my local PHP 5.3.8 and my public host's PHP 5.2.17).
Unfortunately, I haven't got any access either to a server with the latest PHP version. My info is for those of you who like to check things for themselves and who don't believe all of the official statements in the docs.
I've made a simple adjustment of his test code like this:

And it appears to me that simple "$idx=rand(0, count($test)-1);" is much better than "$idx=array_rand($test, 1);".
And what's more the simpler and a bit slower (0 ms up to total 712.357 ms at 5 mln cycles) "rand()" is better than "mt_rand()" in simple everyday use cases because it is more evenly distributed (difference least vs. most often numbers: ca. 0.20-1.28 % for "rand()" vs. ca. 1.43-1.68 % for "mt_rand()").
Try it for yourself... although it depends on your software and hardware configuration, range of numbers to choose from (due to random patterns), number of cycles in the loop, and temporary (public) server load as well.

Generate a random 5 character A-Z0-9 string

# php -r 'for ($i=0; $i

Here's a simple function to generate a random date between a start date and an end date. 
It is inclusive of BOTH dates - so using dates 2009-04-01 and 2009-04-03 would generate a random date that could be 2009-04-01, 2009-04-02 or 2009-04-03.
It won't work if the end date is prior to the start date and if you use a non-existant date (eg 2009-02-30) it defaults to 1970-01-01
the longer version:

and the one-line version for compactness freaks:

it is called like this 

Hope this is of some use to someone

Another one-liner to generate strings:

The strings can be repeated to have the possibility that a character appears multiple times.

As an further optimization on janoserki[at]gmail[dot]com previous post i would recommend that you optimize you first part of php/sql code to something like this.

the count(*) is much faster for the database than grabbing the hole dataset from the table.

Easy way for mysql: random row
the original form is: "... order by rand()"
but this is not the best way, because it's very slow by a big database (it can take more minutes to complete the request!)
My suggestion: 

Much easier way to generate random string of numbers and letters:

This generates strings of about 11 characters. Experiment with the range for rand() if you want shorter or longer.

well ,
this is my vision about "custom random string" : 

Lately I needed some random numbers with a gaussian (normal) distribution, not evenly distributed as the numbers generated by rand(). After googling a while, I found out that there is no perfect algrorithm that creates such numbers out of evenly distruted random numbers but a few methods that have similar effect. The following function implements all three algorithms I found- The the last two methods create numbers where you can find a lower and upper boundary and the first one will create a number from time to time (such as one in every 10000) that may be very far from the average value. Have fun testing and using it. 

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