PHP rand(10000000000000,9999999999999) returning "-114888782"

Question

So, I have a PHP script:

<?
rand(1000000000000,9999999999999);

The expected result is a number with 13 digits.

But it's returning some weird numbers, as:

987419207
1032717476
-455563764

Does anyone know what's going on?

PHP: 5.2.17

OS: Tested on Debian Squeeze and Windows 7, both 64 bits

Solution (workaround)

<?
echo rand(10000,99999).rand(10000000,99999999);

Did you check PHP_INT_MAX? Maybe for some reason you are exceeding int max, even though it should be larger on 64 bit — HashtagMarkus, Dec 10 '12 at 14:22
Overflow plus the fact that 10000000000000 > 9999999999999 will not work, indeed. — Thomas Ruiz, Dec 10 '12 at 14:24
The largest random number PHP can generate is 2147483647 (or 32767 on some system), so you can not generate 13-digit random numbers. But you can check this answer for a workaround http://stackoverflow.com/questions/1479823/in-php-how-do-i-generate-a-big-pseudo-random-number — Hoang Huynh, Dec 10 '12 at 14:29
Take this link http://stackoverflow.com/questions/1587799/why-would-rand-return-a-negative-value-when-min-and-max-values-are-positive It will help you much in understanding. — anuj arora, Dec 10 '12 at 14:38

Luis Tellez · Accepted Answer · 2012-12-10T14:38:28.417

5

Use getrandmax() to see the max value that you can get from rand(), its clearly a overflow problem.

you could use 2 of this int and make a longer one, calling rand for a 6 digit and again for a 7 digits, just an idea.

edited Dec 10 '12 at 14:38

answered Dec 10 '12 at 14:21

Luis Tellez

2147483647. How do I increase this? – dmmd Dec 10 '12 at 14:28
i dont belive you can, but you could use 2 of this int and make a longer one, calling rand for a 6 digit and again for a 7 digits, just an idea. – Luis Tellez Dec 10 '12 at 14:30
64-bit php on 64-bit hardware may help - it would certainly provide 64-bit integers (and that number is the max 32-bit signed integer value) [See here](http://stackoverflow.com/questions/864058/how-to-have-64-bit-integer-on-php) – Basic Dec 10 '12 at 14:32
What I have here is *supposed* to be a 64bit hardware. Go figure. Anyway... I just did rand().rand() with 4 digits in one and 9 in the other. It works. Thanks – dmmd Dec 10 '12 at 14:34
and still the other answer with my information is the + 5 and mine +1 haha. – Luis Tellez Dec 10 '12 at 14:35
The dot (concatenation operator) makes the result return as a string. – dmmd Dec 17 '12 at 16:08

score 4 · Answer 2 · edited Dec 10 '12 at 14:22

4

i think 10000000000000 its not a valid integer!

output

getrandmax();

edited Dec 10 '12 at 14:22

Mihai Matei

answered Dec 10 '12 at 14:21

silly

score 0 · Answer 3 · answered Dec 10 '12 at 14:35

0

Use a bignum library like BCMath or GMP. GMP is newer and seems to have a better API but that's just my opinion

answered Dec 10 '12 at 14:35

Basic

1

I'm going with the workaround here... I don't need anything fancy for this atm. Thanks! – dmmd Dec 10 '12 at 14:37