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 Last updated: Sun, 19 May 2013

# rand

(PHP 4, PHP 5)

randGenerate a random integer

### Description

int rand ( void )
int rand ( int `\$min` , int `\$max` )

If called without the optional `min`, `max` arguments rand() returns a pseudo-random integer between 0 and getrandmax(). If you want a random number between 5 and 15 (inclusive), for example, use rand(5, 15).

Note: On some platforms (such as Windows), getrandmax() is only 32767. If you require a range larger than 32767, specifying `min` and `max` will allow you to create a range larger than this, or consider using mt_rand() instead.

### Parameters

`min`

The lowest value to return (default: 0)

`max`

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

### Return Values

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

### Changelog

Version Description
4.2.0The random number generator is seeded automatically.

### Examples

Example #1 rand() example

``` <?phpecho rand() . "\n";echo rand() . "\n";echo rand(5, 15);?> ```

The above example will output something similar to:

```7771
22264
11
```

### Notes

Caution

This function does not generate cryptographically secure values, and should not be used for cryptographic purposes. If you need a cryptographically secure value, consider using openssl_random_pseudo_bytes() instead.

 Last updated: Sun, 19 May 2013

User Contributed Notes rand - [52 notes]
Zak
1 year ago
``` 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 ```
relsqui at armory dot com
8 years ago
``` 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). ```
4 years ago
``` 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 ```
thibault dot debatty at gmail dot com
9 months ago
``` In Suhosin version 0.9.26 (released 2008.08.22) and above: - rand() and srand() are transparently modified to use the Mersenne Twister algorithm with separate state - rand() and mt_rand() have better internal seeding - srand() and mt_srand() are ignored (can be configured) ```
matthias dot isler at gmail dot com
1 year ago
``` 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); } ?> ```
shiawase at gmail dot com
1 year ago
``` 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. ```
szeryf.wordpress.com
2 years ago
``` 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. ```
Anonymous
3 years ago
``` 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 ```
whatchildisthis at gmail dot com
4 years ago
``` 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 ```
opbarnes
4 years ago
``` Generate a random 5 character alpha string: <?php print preg_replace('/([ ])/e', 'chr(rand(97,122))', '     '); ?> ```
Anonymous
4 years ago
``` 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 ```
davidsteinsland [at] gmail [dot] com
5 years ago
``` 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; ```
Ishtar
5 years ago
``` 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. ```
bozo_z_clown at yahoo dot com
5 years ago
``` 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. ```
ludicruz at yahoo dot com
6 years ago
``` 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); } ?> ```
phpdev at dunnbypaul dot net
6 years ago
``` 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. ```
matheus at matheusloureiro dot com
3 months ago
``` If you are looking for generate a random expression, like password with alphanumeric or any other character, use this function: <?php function GeraHash(\$qtd){ //Under the string \$Caracteres you write all the characters you want to be used to randomly generate the code. \$Caracteres = 'ABCDEFGHIJKLMOPQRSTUVXWYZ0123456789'; \$QuantidadeCaracteres = strlen(\$Caracteres); \$QuantidadeCaracteres--; \$Hash=NULL;     for(\$x=1;\$x<=\$qtd;\$x++){         \$Posicao = rand(0,\$QuantidadeCaracteres);         \$Hash .= substr(\$Caracteres,\$Posicao,1);     } return \$Hash; } //Here you specify how many characters the returning string must have echo GeraHash(30); ?> ```
liveonaware [at] gmail [dot] com
2 years ago
``` <?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; ?> ```
kyle dot florence [@t] gmail dot com
4 years ago
``` 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; } ?> ```
Alex Khimch alex at khim dot removeit dot ich dot org
2 years ago
``` 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. ```
John Galt
3 years ago
``` 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;  } ?> ```
david [at] ddrewdesign [dot] com
3 years ago
``` 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. ```
Justin Richer
1 year ago
``` 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 ```
Hayley Watson
3 months ago
``` The Windows rand() function is quite a lot worse than merely having a low maximum value. It's an ordinary Linear Congruential Generator, which means you only need three consecutive values to be able to predict its entire future output. Given the numbers 13050,  4267,  25352, construct the equations 4267 = (13050a+c) % 32768 25352 = (4267a+c) % 32768 Solving for a and c gives a = 20077 c = 12345 Which means the next number that should be spat out is (25352Ã—20077+12345) % 32768 = 19105 -- which indeed it is. It's not the small rand_max that breaks the algorithm, it's a weakness in the  LCG algorithm itself. It's designed for when you only want a few kinda-random numbers occasionally, not if you want to generate any random-looking data. ```
2 years ago
``` 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; } ?> ```
Hugo Scott hrmscott at hotmail dot com
3 years ago
``` 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.
3 years ago
``` 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"; } ?> ```
petabyte.se
4 years ago
``` 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. ```
jont at live dot co dot uk
6 years ago
``` 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 ```
smaaps at kaldamar dot de
7 years ago
``` 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;      }       } ?> ```
-1
janoserki [at] gmail [dot] com
4 years ago
``` 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 :) ?> ```
-1
umpalump at poczta dot neostrada dot pl
7 years ago
``` 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 ```
-2
5 years ago
``` Hi All, For those whom wants to get a random value from MySQL: select coumnName from TableName order by rand() ```
-1
jamiem123q at gmail dot com
11 months ago
``` I've written a really simple function for generating a specific digit random number. <?php  function RandNumber(\$e){      for(\$i=0;\$i<\$e;\$i++){  \$rand =  \$rand .  rand(0, 9);   }  return \$rand;  }  echo RandNumber(6); // Outputs a 6 digit random number  echo RandNumber(10); // Outputs a 10 digit random number ?> ```
-1
Daniel Klein.
1 year ago
``` 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. ```
-1
Hamza Kubba
1 year ago
``` 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)); // ... ?> ```
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Jesse
2 years ago
``` 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);     // ... } ?> ```
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mike at marylandwebsites dot net
3 years ago
``` 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"; ?> ```
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amossoma at o2 dot pl
4 years ago
``` <?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;   } ?> ```
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szczepan[DoT]Krol #HT# gmail [knowRest]
4 years ago
``` 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>"; ?> ```
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gacek at my dot planet
4 years ago
``` 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];     } } ?> ```
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Anonymous
5 years ago
``` 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; } ?> ```
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Anonymous
5 years ago
``` 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. ```
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rok dot kralj at gmail dot com
5 years ago
``` 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))); } ?> ```
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Patrick Daryll G.
6 years ago
``` 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. ```
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thomas at tgohome dot com
4 years ago
``` 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. ```
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Simon
11 months ago
``` I've written my own rand()-function, it also works very fine: <?php function random(\$min, \$max) {   // md5() generates a hexadecimal number, so we must convert it into base 10   \$rand = base_convert( md5( microtime() ), 16, 10);   // the modulus operator doesn't work with great numbers, so we have to cut the number   \$rand = substr(\$rand, 10, 6);   \$diff = \$max - \$min + 1;   return (\$rand % \$diff) + \$min; } // test: \$arr = array(); for (\$i = 0; \$i < 1000; \$i++) {   \$arr[random(1, 10)]++; } for (\$i = 1; \$i <= 10; \$i++)   echo '<br />' . \$i . ': ' . \$arr[\$i] . "\n"; ?> expected result would be about 100, my result: 1: 108 2: 100 3: 105 4: 92 5: 101 6: 88 7: 93 8: 114 9: 102 10: 97 ```
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djindjojlo AT gmail DOT com
3 years ago
``` 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)];  ?> ```
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alex at bimpson dot com
3 years ago
``` 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. ```
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``` 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 ```
``` <?php /*  * These random number methods are compared by  * the GD-Lib. It shows how random these numbers  * are really. The worst random generator is  * rand().  *  * Usage:  * index.php?type=mt    mt_rand()  * index.php?type=md5    rnd()  * index.php?type=lfrs    lfrs()  * index.php            rand()  */ /* Config */ \$size = 1000; // Size of the Image \$counts = 100000; // Counts of Pixels \$bits = 32; // Bits in the LFRS /* Image creation */ header("Content-type: image/png"); \$im = @imagecreate(\$size, \$size); \$background_color = imagecolorallocate(\$im, 255, 255, 255); \$pixel = imagecolorallocate(\$im, 0, 0, 0); \$size_len = strlen(\$size) - 1; \$chars = 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"); \$shift_register = 1; \$mask = 0x02300282; /* Functions */ function rnd(\$i) {     /* This is a random number by microtime()      * with a startvalue (\$i). This output gets      * hashed with md5() and the chars will all      * be deleted      */     global \$chars, \$size_len;     \$x = md5(\$i . time());     foreach (\$chars AS \$z) {         \$x = str_replace(\$z, "", \$x);     }     return substr(\$x, 0, \$size_len); } function lfrs() {     /* This is a random number by a LFRS      * (linear feedback shift register) it      * is based on a startvalue and a bit-wise      * shift with XOR and AND.      */     global \$shift_register, \$mask;     if (\$shift_register & 0x00000001) {         \$shift_register = (\$shift_register ^ \$mask)>>1 | \$shift_register[1];         return 1;     } else {         \$shift_register>>=1;         return 0;     } } /* Execution */ if (isset(\$_GET["type"]) && \$_GET["type"] == "mt") {     // Random Numbers by mt_rand()     for (\$i = 0; \$i < \$counts; \$i++) {         imagesetpixel(\$im, mt_rand(0, \$size), mt_rand(0, \$size), \$pixel);     } } elseif (isset(\$_GET["type"]) && \$_GET["type"] == "md5") {     // Random Numbers by rnd()     for (\$i = 0; \$i < \$counts; \$i++) {         imagesetpixel(\$im, rnd(\$i), rnd(\$i + \$counts), \$pixel);     } } elseif (isset(\$_GET["type"]) && \$_GET["type"] == "lfrs") {     // Random Numbers by lfrs()     for (\$i = 0; \$i < \$counts; \$i++) {         \$bit = "";         for (\$j = 0; \$j < \$bits; \$j++)             \$bit .= lfrs();         \$ax = substr(base_convert(\$bit, 2, 10), 5, \$size_len);         \$bit = "";         for (\$j = 0; \$j < \$bits; \$j++)             \$bit .= lfrs();         \$ay = substr(base_convert(\$bit, 2, 10), 5, \$size_len);         imagesetpixel(\$im, \$ax, \$ay, \$pixel);     } } else {     // Random Numbers by rand()     for (\$i = 0; \$i < \$counts; \$i++) {         imagesetpixel(\$im, rand(0, \$size), rand(0, \$size), \$pixel);     } } imagepng(\$im); ?> ```
``` 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 ```