PHP generating random numbers

Question

I need to generate about 5,000 random numbers in my script, but the CPU is so fast that I see tendencies in my random numbers.

For example, in the 100 first iterations, I get 80 values between 70 and 99 with rand(0,100);, which can be a REAL inconvenient.

Is there a way to solve such issue, or is randomness not achievable anymore in 2012?

I believe there could be a possibility of generating random numbers from a function executing a random number of times... but I can't figure out one.

What are you using the random numbers for? Their purpose might lead answers in the right direction — Ja͢ck, May 10 '12 at 04:30
@Jack I use random numbers to determine a method according to complex probabilities. — Adam Strudwick, May 10 '12 at 04:33
possible duplicate of [Better Random Generating PHP](http://stackoverflow.com/questions/5611/better-random-generating-php) — CharlesB, May 18 '12 at 08:44

score 5 · Accepted Answer · edited May 23 '17 at 10:30

5

Are you using rand()? Consider "generating a better random value".

Addendum; it's always good to see two sides of a coin.

edited May 23 '17 at 10:30

Community

1
1

answered May 10 '12 at 04:25

Dan Lugg

20,192
19
110
174

I am using rand(). mt_rand generates 4x faster, so it should help. Thanks – Adam Strudwick May 10 '12 at 04:27

score 1 · Answer 2 · answered May 10 '12 at 04:27

rand is seeded by time. mt_rand may work better for you. If you want even better randomness, you can use openssl_random_pseudo_bytes (if available) or /dev/[u]random if you don't have access to that and are on a system where it is available. If you use those, you have to convert the bytes with hexdec(bin2hex()) to get decimal digits, and probably truncate them after that.

score 0 · Answer 3 · answered May 10 '12 at 04:26

0

mt_rand() is an improvement over rand(). But, random numbers are generated from a sequence, so...

answered May 10 '12 at 04:26

goat

31,486
7
73
96

score 0 · Answer 4 · answered Oct 25 '13 at 22:39

0

Use this function :

function Random($length = 210) {
$characters = '0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ';
$randomString = '';
for ($i = 0; $i < $length; $i++) {
    $randomString .= $characters[rand(0, strlen($characters) - 1)];
}
return $randomString;
}

You can change 210 to any number you want hope this helps

answered Oct 25 '13 at 22:39

Dustin.php

11
6

If you're just going to copy/paste and then change function names, at least cite where you copied it from: http://stackoverflow.com/a/4356295/1400370 – Jamie Taylor Oct 29 '13 at 10:53

PHP generating random numbers

4 Answers4