C++ Random Number: What are good random number generators?

[KevinHall]

Q: What are good random number generators?

A: There are two common problems when using pseudo-random number generators (PRNGs):

The PRNG does not get seeded. Please see related FAQ (http://www.codeguru.com/forum/showthread.php?s=&threadid=284875) for discussion on this topic.

A poor PRNG is being used.

This FAQ addresses the second problem.

Often people use the C library function 'rand()' for random number generation. And quite often, the implementation for 'rand()' is not very good - the range of numbers is too small, the period before repetition is too small, and/or other problems.

Better PRNGs can be found in a variety of sources. The most popular is the "Mersenne Twister". The "Mersenne Twister" and other good PNRGs can be found in the Boost library (http://www.boost.org/libs/random/) and the GNU Scientific Library (http://www.gnu.org/software/gsl)).

Another good resource on random number generation is the book "Numerical Recipes in C". It contains a very good discussion on how one can create different distributions based on a uniform random deviate.
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[jwalto1]

Additionally, Wei Dai provides PRNG in his Crypto++ library located at www.cryptopp.com.

Typical code would look as follows:

#include "osrng.h"

using namespace CryptoPP;
.
.
.
AutoSeededRandomPool rng;
byte randomBytes[10];
rng.GenerateBlock(randomBytes, 10);

Otherwise you should use RandomPool and seed it yourself with random, unpredictable data:


RandomPool rng;
rng.Put(seed, seedLen);
byte randomBytes[10];
rng.GenerateBlock(randomBytes, 10);
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