Math 函数
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rand

(PHP 4, PHP 5)

rand — 产生一个随机整数

说明

int rand ([ int $min ], int $max )

如果没有提供可选参数 min 和 max，rand() 返回 0 到 RAND_MAX 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)。

Example #1 rand() example

<?php
echo rand() . "\n";
echo rand() . "\n";

echo rand(5, 15);
?>

以上例程的输出类似于：

7771
22264
11

Note: 在某些平台下（例如 Windows）RAND_MAX 只有 32768。如果需要的范围大于 32768，那么指定 min 和 max 参数就可以生成大于 RAND_MAX的数了，或者考虑用 mt_rand() 来替代之。

Note:

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 rand (5, 11)。

参见 srand()，getrandmax() 和 mt_rand()。

参数

min

The lowest value to return (default: 0)

max

The highest value to return (default: getrandmax())

返回值

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

更新日志

版本 说明
4.2.0随机数发生器自动进行播种。

范例

Example #2 rand() example

<?php
echo rand() . "\n";
echo rand() . "\n";

echo rand(5, 15);
?>

以上例程的输出类似于：

7771
22264
11

参见

Math 函数
在线手册：中文 英文
PHP手册
PHP手册 - N: 产生一个随机整数

用户评论:

Justin Richer (28-Mar-2012 09:43)

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

matthias dot isler at gmail dot com (28-Feb-2012 11:44)

I had to create a function that generates a random binominal distributed integer. Take a look at the following Wiki article:

http://en.wikipedia.org/wiki/Binomial_distribution

Here is my solution:

<?php

function bin_rand($min = null, $max = null)
{
    $min = ($min) ? (int) $min : 0;
    $max = ($max) ? (int) $max : PHP_INT_MAX;
   
    $range = range($min, $max);
    $average = array_sum($range) / count($range);
   
    $dist = array();
    for ($x = $min; $x <= $max; $x++) {
        $dist[$x] = -abs($average - $x) + $average + 1;
    }
   
    $map = array();
    foreach ($dist as $int => $quantity) {
        for ($x = 0; $x < $quantity; $x++) {
            $map[] = $int;
        }
    }
   
    shuffle($map);
    return current($map);
}

?>

Zak (02-Oct-2011 04:34)

I couldn't find a suitable random alpha-numeric generator function so I rolled my own. It gives a random number in base 36 (0-9, a-z) to a given length.

<?php
function randomAlphaNum($length){

    $rangeMin = pow(36, $length-1); //smallest number to give length digits in base 36
    $rangeMax = pow(36, $length)-1; //largest number to give length digits in base 36
    $base10Rand = mt_rand($rangeMin, $rangeMax); //get the random number
    $newRand = base_convert($base10Rand, 10, 36); //convert it
   
    return $newRand; //spit it out

}
?>

hopefully helps someone

Daniel Klein. (19-Aug-2011 11:10)

rand() has a granularity of getrandmax() which means that if you're on a Windows system where getrandmax()==32767 then specifying a range greater than 0-32767 will still only give 32768 unique values. Specifying min=0 and max > getrandmax()+1 where max == 2^n or max == 2^n-1 will return numbers that are multiples of some 2^m where (getrandmax()+1) * 2^m == 2^n.

<?php
function gcd($x, $y) { // If gmp_gcd() is not available
  for (;;) {
    if ($x == 0) return $y;
      else $y %= $x;
    if ($y == 0) return $x;
      else $x %= $y;
  }
}

//$rand_max = 0xFFFFFE; // This gives 1
  $rand_max = 0xFFFFFF; // This gives 512
  $rand_max = 0x1000000; // This gives 512
//$rand_max = 0x1000001; // This gives 1

$gcd = rand(0, $rand_max);
for ($i = 0; $i < 1000; ++$i) {
  $gcd = gcd($gcd, rand(0, $rand_max));
}
print($gcd);
?>

I would suggest always using mt_rand() instead as a good habit to get into.

shiawase at gmail dot com (02-Aug-2011 03:32)

Another one-liner to generate strings:
<?php
substr(str_shuffle(str_repeat('ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789',5)),0,5);
?>
The strings can be repeated to have the possibility that a character appears multiple times.

ilya dot iz at i dot ua (27-Jul-2011 04:09)

I had to come up with a quick way to get a random row from a table, and came up with the following:

<?php
$query = "SELECT `id` FROM [TABLE]";
$result = mysql_query($query, $link);
$num = mysql_num_rows($result);
if ($num > 0) {
    // Array the ID's...
    $id_array = array();
    while ($row = mysql_fetch_assoc($result)) {
        $id_array []=$row["id"];
    }
    $query = "SELECT * FROM [TABLE] WHERE `id`=".$id_array[rand(0, (count($id_array)-1))];
    $result = mysql_query($query, $link);
    $row = mysql_fetch_assoc($result);
    // ...
}
?>

LOL
SELECT * from [TABLE] ORDER BY rand() LIMIT 1

Hamza Kubba (27-May-2011 02:47)

Regarding getting a random row from a table in MySQL (or Postgres), it is better to offload that to the database rather than doing one query to grab tons of data from the database, then a second query to fetch one row.

I.e., this is far more efficient for small to medium sized tables (i.e. less than 1 mil. rows):

SELECT * FROM [TABLE] ORDER BY RAND() LIMIT 1;

For large tables, this is both easy to implement and efficient:

SELECT COUNT(id) AS number_of_rows FROM [TABLE];

then something alone the lines of:

<?php
$sql = "SELECT * FROM [TABLE] LIMIT 1 OFFSET ".(rand(0, $number_of_rows - 1));
// ...
?>

Alex Khimch alex at khim dot removeit dot ich dot org (19-Mar-2011 09:41)

Random is NOT actually random.

It is easily illustrated by multiplying rand(1,500) by rand(1,500) and showing the output on the image:

<?php
header("Content-type: image/png");
$img = imagecreatetruecolor(500,500);

$ink = imagecolorallocate($img,255,255,255);

for($i=0;$i<500;$i++) {
  for($j=0;$j<500;$j++) {
  imagesetpixel($img, rand(1,500), rand(1,500), $ink1);
  }
}

imagepng($img);
imagedestroy($img);

?>

I expected to get pixel noise, but instead one can see plain diagonal lines.

szeryf.wordpress.com (24-Feb-2011 07:26)

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

<?php
$n = rand(10e16, 10e20);
echo base_convert($n, 10, 36);
?>

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

Jesse (22-Dec-2010 07:13)

I had to come up with a quick way to get a random row from a table, and came up with the following:

<?php
$query = "SELECT `id` FROM [TABLE]";
$result = mysql_query($query, $link);
$num = mysql_num_rows($result);
if ($num > 0) {
    // Array the ID's...
    $id_array = array();
    while ($row = mysql_fetch_assoc($result)) {
        $id_array []=$row["id"];
    }
    $query = "SELECT * FROM [TABLE] WHERE `id`=".$id_array[rand(0, (count($id_array)-1))];
    $result = mysql_query($query, $link);
    $row = mysql_fetch_assoc($result);
    // ...
}
?>

Alireza Eliaderani (10-Sep-2010 10:18)

Random integers with normal distribution,
it's not scientifically approved, but worked for me.

<?php
/*
* @param float  $mean, desired average
* @param number $sd, number of items in array
* @param number $min, minimum desired random number
* @param number $max, maximum desired random number
* @return array
*/
function array_distribute($mean,$sd,$min,$max){
    $result = array();
    $total_mean = intval($mean*$sd);
    while($sd>1){
        $allowed_max = $total_mean - $sd - $min;
        $allowed_min = intval($total_mean/$sd);
        $random = mt_rand(max($min,$allowed_min),min($max,$allowed_max));
        $result[]=$random;
        $sd--;
        $total_mean-=$random;
    }
    $result[] = $total_mean;
    return $result;
}
?>

liveonaware [at] gmail [dot] com (01-Jun-2010 04:16)

<?php
//To Pull 7 Unique Random Values Out Of AlphaNumeric

//removed number 0, capital o, number 1 and small L
//Total: keys = 32, elements = 33
$characters = array(
"A","B","C","D","E","F","G","H","J","K","L","M",
"N","P","Q","R","S","T","U","V","W","X","Y","Z",
"1","2","3","4","5","6","7","8","9");

//make an "empty container" or array for our keys
$keys = array();

//first count of $keys is empty so "1", remaining count is 1-6 = total 7 times
while(count($keys) < 7) {
    //"0" because we use this to FIND ARRAY KEYS which has a 0 value
    //"-1" because were only concerned of number of keys which is 32 not 33
    //count($characters) = 33
    $x = mt_rand(0, count($characters)-1);
    if(!in_array($x, $keys)) {
       $keys[] = $x;
    }
}

foreach($keys as $key){
   $random_chars .= $characters[$key];
}
echo $random_chars;
?>

Anonymous (06-Mar-2010 02:41)

Generate a random 5 character A-Z0-9  string

<?php
for ($i=0; $i<6; $i++) {
    $d=rand(1,30)%2;
    echo $d ? chr(rand(65,90)) : chr(rand(48,57));
}
?>

# php -r 'for ($i=0; $i<6; $i++) { $d=rand(1,30)%2; echo $d ? chr(rand(65,90)) : chr(rand(48,57)); } echo "\n";'
14BW1A

mike at marylandwebsites dot net (24-Feb-2010 02:42)

Rather then counting the rows or running the RAND in my query, I find this to work just fine.
This code is used to display business highlights at random

Would love to get feedback on this

<?php
// First get the last id from the table

$SQL = "SELECT * FROM HIGHLIGHTS ORDER BY highlight_id DESC LIMIT 1";
$result = mysql_query( $SQL );
while( $row = mysql_fetch_array( $result ) ) {
$ending_id = $row["highlight_id"];
}

// I only want the 5 most recent entries
// So I just subtract 5 from the last ID

$starting_id = $ending_id - 5;

// Because I we don't want a nagitive number I just
// make sure that the starting ID is at least 1

if($starting_id <= 0){
    $starting_id = "1";
    }
 
// now I run the the $starting_id $ending_id at RAND

$howey = rand($starting_id, $ending_id);

// Now I use howey as my id

$SQL = "SELECT * FROM HIGHLIGHTS WHERE highlight_id = '$howey'";
$result = mysql_query( $SQL );
while( $row = mysql_fetch_array( $result ) ) {
$highlight_id = $row["highlight_id"];
$highlight_title = $row["highlight_title"];
}
echo "$highlight_id $highlight_title";
?>

djindjojlo AT gmail DOT com (20-Feb-2010 01:52)

a very easy random letters and numbers... one of my beginers scripts :)

<?php

$abc= array("a", "b", "c", "d", "e", "f", "g", "h", "i", "j", "k", "l", "m", "n", "o", "p", "q", "r", "s", "t", "u", "v", "w", "x", "y", "z");
$num= array("0", "1", "2", "3", "4", "5", "6", "7", "8", "9");
echo $abc[rand(0,25)];
echo $num[rand(0,9)]; 
?>

John Galt (02-Jan-2010 07:24)

Another way to create an array of random numbers where there are no identical numbers.

($n = number of random numbers to return in the array
$min = minimum number
$max = maximum number)

<?php
 function uniqueRand($n, $min = 0, $max = null)
 {
  if($max === null)
   $max = getrandmax();
  $array = range($min, $max);
  $return = array();
  $keys = array_rand($array, $n);
  foreach($keys as $key)
   $return[] = $array[$key];
  return $return;
 }
?>

Hugo Scott hrmscott at hotmail dot com (29-Jul-2009 03:52)

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:
<?php
function makeRandomDateInclusive($startDate,$endDate){
    $days = round((strtotime($endDate) - strtotime($startDate)) / (60 * 60 * 24));
    $n = rand(0,$days);
    return date("Y-m-d",strtotime("$startDate + $n days"));   
}
?>

and the one-line version for compactness freaks:
<?php
function makeRandomDateInclusive($startDate,$endDate){   
    return date("Y-m-d",strtotime("$startDate + ".rand(0,round((strtotime($endDate) - strtotime($startDate)) / (60 * 60 * 24)))." days"));
}
?>

it is called like this
<?php
echo makeRandomDateInclusive('2009-04-01','2009-04-03');
?>
Hope this is of some use to someone

Greg R. (16-Jun-2009 12:49)

I thought this function (random color) might be of use to someone [to create and return a random hex for HTML colors]:

<?php
function get_random_color()
{
    for ($i = 0; $i<6; $i++)
    {
        $c .=  dechex(rand(0,15));
    }
    return "#$c";
}
?>

alex at bimpson dot com (15-Jun-2009 05:30)

A very easy method for generating for generating an array of UNIQUE random numbers:

<?php

$rand = array();
while (count($rand) < $total ) {
    $r = mt_rand($min,$max);
    if ( !in_array($r,$rand) ) {
        $rand[] = $r;
    }
}

?>

whereby $total is the number of unique random numbers you want, $min is the lowest possible value and $max is the highest possible value.

david [at] ddrewdesign [dot] com (27-May-2009 02:21)

To Jano and Peta:

Thanks for the code. In real world usage, I only had one problem with it: It will never return the first result of the array (or it will return nothing if there's only one item in the array). To remedy this, I simply subtracted 1 from

<?php
$rand = rand(1,$max);
?>

like so:

<?php
$rand = rand(1,$max)-1;
?>

Thanks though, for the code you supplied. It was exactly what I needed.

kyle dot florence [@t] gmail dot com (08-May-2009 11:23)

Improved random string generation function:

<?php
// Generate a random character string
function rand_str($length = 32, $chars = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz1234567890')
{
    // Length of character list
    $chars_length = (strlen($chars) - 1);

    // Start our string
    $string = $chars{rand(0, $chars_length)};
   
    // Generate random string
    for ($i = 1; $i < $length; $i = strlen($string))
    {
        // Grab a random character from our list
        $r = $chars{rand(0, $chars_length)};
       
        // Make sure the same two characters don't appear next to each other
        if ($r != $string{$i - 1}) $string .=  $r;
    }
   
    // Return the string
    return $string;
}
?>

admin at djs-music dot com (25-Apr-2009 06:13)

A nice function to generate a random string, using any character:

<?php
function generateRandStr($length){
      $randstr = "";
      for($i=0; $i<$length; $i++){
         $randnum = mt_rand(0,61);
         if($randnum < 10){
            $randstr .= chr($randnum+48);
         }else if($randnum < 36){
            $randstr .= chr($randnum+55);
         }else{
            $randstr .= chr($randnum+61);
         }
      }
      return $randstr;
   }
?>

Simply use:
generateRandStr(10);

Sample output: $%29zon(4f

petabyte.se (15-Mar-2009 04:56)

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.

<?php
// estimate the number of rows in a table
$lekerdezes = mysql_query("select count(*) as rows from table");
while ($row = mysql_fetch_assoc($lekerdezes))
{
    $max = $row["rows"];
}
?>
the count(*) is much faster for the database than grabbing the hole dataset from the table.

janoserki [at] gmail [dot] com (04-Mar-2009 08:16)

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:

<?php
// estimate the number of rows in a table
$lekerdezes = mysql_query("select * from table");
$max = mysql_num_rows($lekerdezes);

// pick one
$rand = rand(1,$max);

$lekerdezes2 = mysql_query("select * from table limit $rand, 1");

// that's all folks :)

?>

whatchildisthis at gmail dot com (07-Dec-2008 12:00)

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.

<?php
for ($s = '', $i = 0, $z = strlen($a = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789')-1; $i != 32; $x = rand(0,$z), $s .= $a{$x}, $i++);
?>

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

<?php
for ($i = 0, $z = strlen($a = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz1234567890')-1, $s = $a{rand(0,$z)}, $i = 1; $i != 32; $x = rand(0,$z), $s .= $a{$x}, $s = ($s{$i} == $s{$i-1} ? substr($s,0,-1) : $s), $i=strlen($s));
?>

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

<?php
function rand_chars($c, $l, $u = FALSE) {
 if (!$u) for ($s = '', $i = 0, $z = strlen($c)-1; $i < $l; $x = rand(0,$z), $s .= $c{$x}, $i++);
 else for ($i = 0, $z = strlen($c)-1, $s = $c{rand(0,$z)}, $i = 1; $i != $l; $x = rand(0,$z), $s .= $c{$x}, $s = ($s{$i} == $s{$i-1} ? substr($s,0,-1) : $s), $i=strlen($s));
 return $s;
}
?>

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

adam at greatbigmassive dot com (02-Dec-2008 01:10)

I've noticed alot of people doing long winded random string generators so I thought I'd post my one liner to give a bit of a fresh approach.

The concept is simple. The rand() function generates a number made up of 10 different digits. (0,1,2,3,4,5,6,7,8,9).
To generate an equivalent string I only need 10 alpha characters to replace the numbers.

I am using (p,q,r,s,t,u,v,w,x,y). I chose these letters because they don't include any characters that resemble numbers and was the best set generated by the chr() function.

Anyway, to create a 6 character random string I do this:

$rand = preg_replace("/([0-9])/e","chr((\\1+112))",rand(100000,999999));

The length of the string is based on the length of the random number generated.
This would also mean you could generate a random string at a random length too if you wanted.

Adam

amossoma at o2 dot pl (19-Nov-2008 09:40)

<?php
function generateRandomString($length = 10, $letters = '1234567890qwertyuiopasdfghjklzxcvbnm')
  {
      $s = '';
      $lettersLength = strlen($letters)-1;
     
      for($i = 0 ; $i < $length ; $i++)
      {
      $s .= $letters[rand(0,$lettersLength)];
      }
     
      return $s;
  }
?>

opbarnes (20-Oct-2008 08:33)

Generate a random 5 character alpha string:

<?php
print preg_replace('/([ ])/e', 'chr(rand(97,122))', '     ');
?>

szczepan[DoT]Krol #HT# gmail [knowRest] (14-Aug-2008 02:55)

Heres another function to generate Random Unique numbers.

<?php
class UniqueRand{
  var $alreadyExists = array();

  function uRand($min = NULL, $max = NULL){
    $break='false';
    while($break=='false'){
      $rand=mt_rand($min,$max);

      if(array_search($rand,$this->alreadyExists)===false){
        $this->alreadyExists[]=$rand;
        $break='stop';
      }else{
        echo " $rand already!  ";
        print_r($this->alreadyExists);
      }
    }
    return $rand;
  }
}
$rand=new UniqueRand();


echo"<b> ". $rand->uRand(0,5)."</b>";
echo"<b> ". $rand->uRand(5,5)."</b>";
echo"<b> ". $rand->uRand(10,5)."</b>";

?>

thomas at tgohome dot com (31-Jul-2008 04:46)

You don't need fancy queries to grab a random row(s) from MySQL; it's actually quite simple. In fact, you can do it in a single query.

<?php
$random_rows = array();

$query = mysql_query("SELECT * FROM tablename ORDER BY RAND() LIMIT 1");

while($row = mysql_fetch_array($query))
{
     $random_rows[] = $row;
}
?>

You can extend LIMIT to any number, so you can select 10 random rows. Also, because it uses ORDER BY the rows are always unique if you select 10 rows, for example.

This might work on other database systems such as MsSQL and PostgreSQL but I haven't tested them.

Anonymous (31-Jul-2008 12:29)

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...

<?php

$random_number = intval( "0" . rand(1,9) . rand(0,9) . rand(0,9) . rand(0,9) . rand(0,9) ); // random(ish) 5 digit int

$random_string = chr(rand(65,90)) . chr(rand(65,90)) . chr(rand(65,90)) . chr(rand(65,90)) . chr(rand(65,90)); // random(ish) 5 character string

?>

hope someone finds it useful for somthing.

regards,
deeeeeen alxndr0u

gacek at my dot planet (29-May-2008 12:36)

For some people who would need to generate random string:

<?php

function random_letters ($numofletters) {
    if (!isset($numofletters)) $numofletters = 10; // if $numofletters is not specified sets to 10 letters
    $literki = array('A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K', 'L', 'M', 'N', 'O', 'P', 'R', 'S', 'T', 'U', 'W');
    $ilosc_literek = count($literki);
    for ($licz = 0; $licz < $numofletters; $licz++) {
    $rand = rand(0, $ilosc_literek-1);
    $vercode = $vercode.$literki[$rand];
    }
}

?>

davidsteinsland [at] gmail [dot] com (26-Apr-2008 08:27)

emad_ramahi at hotmail dot com:
I've actually noticed that with a large dataset (100k rows), the query dramatically slows down the server and performance is way too bad.

The way I see it, you have to workable solutions:

Using PHP:

<?php
//$Table holds the name of the table we're getting the random row from
//$Rows specifies how many rows we need to fetch
function mysql_rand ($Query, $Rows = 1) {
    //getting the table name from $query
    //what you can do, is replace the $query argument with $table,
    //this way to dont have to search for the table's name
    $SQL = sprintf ('SELECT COUNT(*) FROM %s', substr ($query, stripos ($query, 'from')+5, strpos ($query, ' ')));
   
    $Max = mysql_result (mysql_query ($SQL), 0);
    $Random = rand (0, $Max);
   
    //If the random number is 99, and the database only has 100 rows
    //We'll subtract the random number, so we don't exceed 100, thus preventing a MySQL error message
    return $Query . sprintf ('LIMIT %d, %d', ($Max < $Rows) ? 0 : (($Random > $Max - $Rows) ? $Max - $Rows : $Random), $Rows);
}

//Instead of using MySQL's RAND(), we use LIMIT to fetch rows
//E.g. LIMIT 5,9 fetches from row 5, and the subsequent 9
$SQL = mysql_rand ('SELECT row FROM table'); //SELECT row FROM table LIMIT x, y
?>

or SQL:
SELECT * FROM Table T JOIN (SELECT FLOOR(MAX(ID)*RAND()) AS ID FROM Table) AS x ON T.ID >= x.ID LIMIT 1;

emad_ramahi at hotmail dot com (09-Mar-2008 09:16)

Hi All,
For those whom wants to get a random value from MySQL:
select coumnName from TableName order by rand()

Anonymous (25-Feb-2008 08:37)

Using the script below with rand() instead of mt_rand(),
I was suprised to find many "words" and part of "phrases" in common.

mt_rand() is highly recomanded when you want to build test cases.

<?php
 $ressbdd = mysql_connect("localhost", "usr", "pass")
  or  die("Could not connect: " . mysql_error());
 for($i=0;$i<100000;$i++){
  $xx1=mt_rand(15,80);
  $texte = phrase($xx1);
  $sql = 'INSERT into phrases.valeurs set valeur = \'' . $texte . '\'';
  mysql_query( $sql , $ressbdd );
 }
//=============================================
function phrase($n){
 $phrase='';
 for($i=0;$i<$n;$i++){
  $xx2=mt_rand(2,20);
  $phrase.=mot($xx2) . ' ';
 }
 return(substr($phrase,0,-1).'.'); // phrase ends with a .
}
//=============================================
function mot($n){
 if($n<=0)  return 'hello';
 if($n>=31) return 'world';
 $voyelle =Array('a','e','i','o','u','y');
 $consonne=Array(
'b','c','d','f','g','h','j','k','l','m',
'n','p','q','r','s','t','v','w','x','z');
 $mot='';
 for($i=0;$i<$n;$i++){
  if($i%2==0){
   $xx3=mt_rand(0,19);
   $mot.=$consonne[$xx3];
  }else{
   $xx4=mt_rand(0,5);
   $mot.=$voyelle[$xx4];
  }
 }
 return $mot;
}
?>

Anonymous (06-Nov-2007 09:24)

Note, the function used by PHP to constrain a random number between (min, max) is the following:

$number = $min + (($max - $min + 1) * ($number / ($rand_max + 1));

where the following:
$number - the initially generated random number
$min - the minimum in the range
$max - the maximum in the range
$rand_max - the maximum possible random value

What this algorithm does is constrain the generated number to a 0-1 range, then multiply it against your range, mapping the two to each other.

In practice you'll see the following results:
For a generated $number of 16384 and a $rand_max of 32768:
rand(0, 10) = 5
rand(0, 100) = 50
rand(0, 1000) = 500

with the additional property that if the range you're asking for is larger than $rand_max, random numbers will be in a multiple of $max/$rand_max.

Ishtar (10-Sep-2007 02:18)

A small comment on phpdev-dunnbypauls conclusion that rand() only generates numbers that are a multiply of 3.
<?php
$n = rand(0,100000); // with MAX_RAND=32768
?>
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.

rok dot kralj at gmail dot com (16-Jun-2007 08:43)

rand function returns just a whole numbers. If you want a random float, then here's an elegant way:

<?php
function random_float ($min,$max) {
   return ($min+lcg_value()*(abs($max-$min)));
}
?>

bozo_z_clown at yahoo dot com (24-May-2007 01:36)

Note that the automatic seeding seems to be done with the current number of seconds which means you can get the same results for several runs on a fast server.  Either call srand() yourself with a more frequently changing seed or use mt_rand() which doesn't appear to suffer from the problem.

jont at live dot co dot uk (05-Apr-2007 11:42)

isn't this just a simpler way of making a random id for somthing? I mean i know that there is a very slight chance that a duplicate could be made but its a very, very, very small chance, nearly impossible.

$rand = mt_rand(0, 32);
$code = md5($rand . time());
echo "$code";

and if you don't want it the md5 can be removed, I've just added it as a prefer it there :)

Jon

phpdev at dunnbypaul dot net (08-Mar-2007 04:51)

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

<?php
$r = array(0,0,0,0,0,0,0,0,0,0,0);
for ($i=0;$i<1000000;$i++) {
  $n = rand(0,100000);
  if ($n<=10) {
    $r[$n]++;
  }
}
print_r($r);
?>

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.

Patrick Daryll G. (02-Mar-2007 02:51)

Using rand()%x is faster than rand(0,x) yes, but it is wrong.
Consider the following example:
RAND_MAX is 32768 (like on Windows for example)
You use rand()%30000
Imagine rand() returns a value between 30000 and 32768.
Modulo could make any value between 0 and 2768, but not any between 2769 and 29999 (except the value is below 29999).
This would double the chance of getting a number between 0 and 2768, which is speaking against the principles of randomness.

ludicruz at yahoo dot com (27-Sep-2006 01:42)

frank, nick at nerdynick dot com, and kniht
this is now O(n) instead of O(n^2) ish...

<?php
function rand_permute($size, $min, $max)
{
    $retval = array();
    //initialize an array of integers from $min to $max
    for($i = $min;$i <= $max;$i++)
    {
        $retval[$i] = $i;
    }
    //start with the the first index ($min).
    //randomly swap this number with any other number in the array.
    //this way we guarantee all numbers are permuted in the array,
    //and we assure no number is used more than once (technically reiterating prev line).
    //therefore we don't have to do the random checking each time we put something into the array.
    for($i=$min; $i < $size; $i++)
    {
        $tmp = $retval[$i];
        $retval[$i] = $retval[$tmpkey = rand($min, $max)];
        $retval[$tmpkey] = $tmp;
    }
    return array_slice($retval, 0, $size);
}
?>

umpalump at poczta dot neostrada dot pl (13-Jun-2005 01:32)

Random numbers with Gauss distribution (normal distribution).
A correct alghoritm. Without aproximations, like Smaaps'
It is specially usefull for simulations in physics.
Check yourself, and have a fun.

<?php

function gauss()
{   // N(0,1)
    // returns random number with normal distribution:
    //   mean=0
    //   std dev=1
   
    // auxilary vars
    $x=random_0_1();
    $y=random_0_1();
   
    // two independent variables with normal distribution N(0,1)
    $u=sqrt(-2*log($x))*cos(2*pi()*$y);
    $v=sqrt(-2*log($x))*sin(2*pi()*$y);
   
    // i will return only one, couse only one needed
    return $u;
}

function gauss_ms($m=0.0,$s=1.0)
{   // N(m,s)
    // returns random number with normal distribution:
    //   mean=m
    //   std dev=s
   
    return gauss()*$s+$m;
}

function random_0_1()
{   // auxiliary function
    // returns random number with flat distribution from 0 to 1
    return (float)rand()/(float)getrandmax();
}

?>

JanS
student of astronomy
on Warsaw University

smaaps at kaldamar dot de (07-Jun-2005 06:44)

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.

<?php
function gauss($algorithm = "polar") {
    $randmax = 9999;
   
    switch($algorithm) {
       
        //polar-methode by marsaglia
        case "polar":
            $v = 2;
            while ($v > 1) {
                $u1 = rand(0, $randmax) / $randmax;
                $u2 = rand(0, $randmax) / $randmax;

                $v = (2 * $u1 - 1) * (2 * $u1 - 1) + (2 * $u2 - 1) * (2 * $u2 - 1);
            }
           
            return (2* $u1 - 1) * (( -2 * log($v) / $v) ^ 0.5);
       
        // box-muller-method
        case "boxmuller":
            do {
                $u1 = rand(0, $randmax) / $randmax;
                $u2 = rand(0, $randmax) / $randmax;                   
               
                $x = sqrt(-2 * log($u1)) * cos(2 * pi() * $u2);
            } while (strval($x) == "1.#INF" or strval($x) == "-1.#INF");
           
            // the check has to be done cause sometimes (1:10000)
            // values such as "1.#INF" occur and i dont know why
           
            return $x;

        // twelve random numbers  
        case "zwoelfer":
            $sum = 0;
            for ($i = 0; $i < 12; $i++) {
                $sum += rand(0, $randmax) / $randmax;
            }
            return $sum;
     }      
}
?>

relsqui at armory dot com (21-Jan-2005 10:23)

Don't forget, it's faster to use bitwise operations when you need a random number that's less than some power of two. For example,

<?php
rand()&1;
// instead of
rand(0,1);
// for generating 0 or 1,

rand()&3;
// instead of
rand(0,3);
// for generating 0, 1, 2, or 3,

rand()&7;
// instead of
rand(0,7)
// for generating 0, 1, 2, 3, 4, 5, 6, or 7,
?>

and so on. All you're doing there is generating a default random number (so PHP doesn't have to parse any arguments) and chopping off the piece that's useful to you (using a bitwise operation which is faster than even basic math).