| // die.cpp |
| // |
| // Copyright (c) 2009 |
| // Steven Watanabe |
| // |
| // Distributed under the Boost Software License, Version 1.0. (See |
| // accompanying file LICENSE_1_0.txt or copy at |
| // http://www.boost.org/LICENSE_1_0.txt) |
| |
| //[die |
| /*` |
| For the source of this example see |
| [@boost://libs/random/example/die.cpp die.cpp]. |
| First we include the headers we need for __mt19937 |
| and __uniform_int. |
| */ |
| #include <boost/random/mersenne_twister.hpp> |
| #include <boost/random/uniform_int.hpp> |
| #include <boost/random/variate_generator.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::mt19937 gen; |
| /*` |
| [note We are using a /global/ generator object here. This |
| is important because we don't want to create a new [prng |
| pseudo-random number generator] at every call] |
| */ |
| /*` |
| Now we can define a function that simulates an ordinary |
| six-sided die. |
| */ |
| int roll_die() { |
| /*<< __mt19937 produces integers in the range [0, 2[sup 32]-1]. |
| However, we want numbers in the range [1, 6]. The distribution |
| __uniform_int performs this transformation. |
| [warning Contrary to common C++ usage __uniform_int |
| does not take a /half-open range/. Instead it takes a /closed range/. |
| Given the parameters 1 and 6, __uniform_int can |
| can produce any of the values 1, 2, 3, 4, 5, or 6.] |
| >>*/ |
| boost::uniform_int<> dist(1, 6); |
| /*<< __variate_generator combines a generator with a distribution. |
| [important We pass [classref boost::mt19937 boost::mt19937&] to |
| __variate_generator instead of just [classref boost::mt19937] |
| (note the reference). Without the reference, __variate_generator |
| would make a copy of the generator and would leave the global |
| `gen` unchanged. Consequently, `roll_die` would produce *the same value* |
| every time it was called.] |
| >>*/ |
| boost::variate_generator<boost::mt19937&, boost::uniform_int<> > die(gen, dist); |
| /*<< A __variate_generator is a function object. >>*/ |
| return die(); |
| } |
| //] |
| |
| #include <iostream> |
| |
| int main() { |
| for(int i = 0; i < 10; ++i) { |
| std::cout << roll_die() << std::endl; |
| } |
| } |