// 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 #include #include /*` 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 > die(gen, dist); /*<< A __variate_generator is a function object. >>*/ return die(); } //] #include int main() { for(int i = 0; i < 10; ++i) { std::cout << roll_die() << std::endl; } }