1 files changed, 46 insertions, 0 deletions
diff --git a/src/boost/libs/mpi/example/string_cat.cpp b/src/boost/libs/mpi/example/string_cat.cpp
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+++ b/src/boost/libs/mpi/example/string_cat.cpp
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+// Copyright (C) 2006 Douglas Gregor <doug.gregor@gmail.com>
+
+// Use, modification and distribution is subject to 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)
+
+// An example using Boost.MPI's reduce() to concatenate strings.
+#include <boost/mpi.hpp>
+#include <iostream>
+#include <string>
+#include <boost/serialization/string.hpp> // Important for sending strings!
+namespace mpi = boost::mpi;
+
+/* Defining STRING_CONCAT_COMMUTATIVE lies to Boost.MPI by forcing it
+ * to assume that string concatenation is commutative, which it is
+ * not. However, doing so illustrates how the results of a reduction
+ * can change when a non-commutative operator is assumed to be
+ * commutative.
+ */
+#ifdef STRING_CONCAT_COMMUTATIVE
+namespace boost { namespace mpi {
+
+template<>
+struct is_commutative<std::plus<std::string>, std::string> : mpl::true_ { };
+
+} } // end namespace boost::mpi
+#endif
+
+int main(int argc, char* argv[])
+{
+  mpi::environment env(argc, argv);
+  mpi::communicator world;
+
+  std::string names[10] = { "zero ", "one ", "two ", "three ", "four ",
+                            "five ", "six ", "seven ", "eight ", "nine " };
+
+  std::string result;
+  reduce(world,
+         world.rank() < 10? names[world.rank()] : std::string("many "),
+         result, std::plus<std::string>(), 0);
+
+  if (world.rank() == 0)
+    std::cout << "The result is " << result << std::endl;
+
+  return 0;
+}