Errors go to stderr

src/one-body-sample.cc

@@ -295,6 +295,6 @@ int main(int argc, char *argv[]) {
     Dune::derr << "Dune reported error: " << e << std::endl;
   }
   catch (std::exception &e) {
-    std::cout << "Standard exception: " << e.what() << std::endl;
+    std::cerr << "Standard exception: " << e.what() << std::endl;
   }
 }