different rand() results on Windows and Linux

Question

Hello ! I've noticed, that standard rand() function gives different results on Windows and Linux. Ofcourse I've used the same seed number (1234). Here are several first results:

WIN: 4068 213 12761 8758

LIN: 479142414 465566339 961126155 1057886067

My application requires that both platforms produce identical output. What are my options? Is there any good replacement for rand() that meets my requirement ?

thanks

PS. I used MSVC 2008 on Windows7, and gcc 4.1.2 on CentOS 5.5

Answer 1

You won't get the same results due to the different implementation of the functions on either platform.

Answer 2

Boost has a wide range of RNGs, presumably with reproducible behaviour across platforms.

Answer 3

• Write your own (not recommended).
• Use a library. e.g. Boost
• This function

Answer 4

You may try srand(int), which generates random number based on seed (input)

-- Cheers

Answer 5

I think you will even find different linux versions returning different values, as well as different windows versions returning different values.

You could unify your random generator by using the glibc one, for example.

Another option for you is writing your own function BUT do that ONLY if you are 100% sure you don't need to use your random for cryptographic use or any other use that requires the thing to have unpredictability or uniformness or otherwise randomish properties.

Answer 6

If you’re happy with the standard rand implementation and only require reproduceability, you can easily write your own linear congruential generator (adapting the C interface, probably not a good choice! – rather use a class instead):

namespace myown {

static int state;

void srand(int seed) {
    state = seed;
}

int rand() {
    int const a = 1103515245;
    int const c = 12345;
    state = a * state + c;
    return (state >> 16) & 0x7FFF;
}

}

This uses constants (ANSI C: Watcom) from the Wikipedia article.

That said, I’d rather go with a read-made implementation from Boost, as proposed by others.