How do you generate random strings in C++?

Question

I am looking for methods to generate random strings in C++.Here is my code:

string randomStrGen(int length) {
    static string charset = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890";
    string result;
    result.resize(length);

    srand(time(NULL));
    for (int i = 0; i < length; i++)
        result[i] = charset[rand() % charset.length()];

    return result;
}

But the seed(time(NULL)) is not random enough.Are there any other better way to generate random strings in C++?

Answer 1

Don't call srand() on each function call - only call it once at first function call or program startup. You migh want to have a flag indicating whethersrand() has already been called.

The sugested method is good except that you misuse srand() and get predictably bad results.

Answer 2

You can use Boost.Random. It uses a different generator than the one provided with most standard libraries, that should be more robust.

In specific, most standard libraries provide linear congruential generators, which don't perform very well when you mod their results with small numbers. Boost.Random has a Mersenne twister generator.

As sharptooth says, though (good spotting!), only seed the generator once, at the very start of your program. Seeding it every time you want something random is counter-productive.

Answer 3

Make an interface to get a random number in this site http://www.random.org/ and you will be sure to get a real random number! But if you are looking for performance...

Answer 4

On unix systems you can read random values from the file /dev/random