1 // Copyright (C) 2006 Douglas Gregor <doug.gregor@gmail.com>
2
3 // Use, modification and distribution is subject to the Boost Software
4 // License, Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at
5 // http://www.boost.org/LICENSE_1_0.txt)
6
7 // An example using Boost.MPI's reduce() to concatenate strings.
8 #include <boost/mpi.hpp>
9 #include <iostream>
10 #include <string>
11 #include <boost/serialization/string.hpp> // Important for sending strings!
12 namespace mpi = boost::mpi;
13
14 /* Defining STRING_CONCAT_COMMUTATIVE lies to Boost.MPI by forcing it
15 * to assume that string concatenation is commutative, which it is
16 * not. However, doing so illustrates how the results of a reduction
17 * can change when a non-commutative operator is assumed to be
18 * commutative.
19 */
20 #ifdef STRING_CONCAT_COMMUTATIVE
21 namespace boost { namespace mpi {
22
23 template<>
24 struct is_commutative<std::plus<std::string>, std::string> : mpl::true_ { };
25
26 } } // end namespace boost::mpi
27 #endif
28
main(int argc,char * argv[])29 int main(int argc, char* argv[])
30 {
31 mpi::environment env(argc, argv);
32 mpi::communicator world;
33
34 std::string names[10] = { "zero ", "one ", "two ", "three ", "four ",
35 "five ", "six ", "seven ", "eight ", "nine " };
36
37 std::string result;
38 reduce(world,
39 world.rank() < 10? names[world.rank()] : std::string("many "),
40 result, std::plus<std::string>(), 0);
41
42 if (world.rank() == 0)
43 std::cout << "The result is " << result << std::endl;
44
45 return 0;
46 }
47