...one of the most highly
regarded and expertly designed C++ library projects in the
world.
— Herb Sutter and Andrei
Alexandrescu, C++
Coding Standards
For the source of this example see die.cpp.
First we include the headers we need for mt19937
and uniform_int_distribution
.
#include <boost/random/mersenne_twister.hpp> #include <boost/random/uniform_int_distribution.hpp>
We use mt19937
with the
default seed as a source of randomness. The numbers produced will be the
same every time the program is run. One common method to change this is to
seed with the current time (std::time(0)
defined in ctime).
boost::random::mt19937 gen;
Note | |
---|---|
We are using a global generator object here. This is important because we don't want to create a new pseudo-random number generator at every call |
Now we can define a function that simulates an ordinary six-sided die.
int roll_die() { boost::random::uniform_int_distribution<> dist(1, 6); return dist(gen); }
|
||||
A distribution is a function object. We generate a random number by calling
|
For the source of this example see weighted_die.cpp.
#include <boost/random/mersenne_twister.hpp> #include <boost/random/discrete_distribution.hpp> boost::mt19937 gen;
This time, instead of a fair die, the probability of rolling a 1 is 50% (!). The other five faces are all equally likely.
discrete_distribution
works nicely here by allowing us to assign weights to each of the possible
outcomes.
Tip | |
---|---|
If your compiler supports |
double probabilities[] = { 0.5, 0.1, 0.1, 0.1, 0.1, 0.1 }; boost::random::discrete_distribution<> dist(probabilities);
Now define a function that simulates rolling this die.
int roll_weighted_die() { return dist(gen) + 1; }
For the source of this example see password.cpp.
This example demonstrates generating a random 8 character password.
#include <boost/random/random_device.hpp> #include <boost/random/uniform_int_distribution.hpp> int main() { std::string chars( "abcdefghijklmnopqrstuvwxyz" "ABCDEFGHIJKLMNOPQRSTUVWXYZ" "1234567890" "!@#$%^&*()" "`~-_=+[{]}\\|;:'\",<.>/? "); boost::random::random_device rng; boost::random::uniform_int_distribution<> index_dist(0, chars.size() - 1); for(int i = 0; i < 8; ++i) { std::cout << chars[index_dist(rng)]; } std::cout << std::endl; }
We first define the characters that we're going to allow. This is pretty much just the characters on a standard keyboard. |
|
We use |
|
Finally we select 8 random characters from the string and print them to cout. |