Example 1: Driver

As a runtime abstraction layer, FleCSI replaces the normal main function with a driver function. Like main, the driver is the most fundamental unit of execution, providing the top-level control logic for the user’s code. There is still a main function as required by C/C++. However, in a FleCSI application, it is normally handled by the specialization layer, or, in the case of this tutorial, by the flecsit compiler script, which uses the runtime_main.cc file that is installed as part of FleCSI under the share/FleCSI/runtime directory. Applications can choose to either use this default main function, or replace it with their own (if more explicit control is needed).

This example’s driver prints out the canonical Hello World with whatever arguments the user has passed to the command line. Command-line arguments are passed through the FleCSI runtime to the user’s driver as with a normal main function.

Try compiling this example with flecsit:

$ flecsit compile driver.cc

You can run it like:

$ ./driver arg1 arg2

You can experiment with changing the output or handling of the command-line arguments.


  • All drivers must be defined in the flecsi::execution namespace.

The code for this example can be found in driver.cc:

#include <iostream>

namespace flecsi {
namespace execution {

void driver(int argc, char ** argv) {

  // Print the message

  std::cout << "Hello World" << std::endl;

  // Print the arguments that were passed on the command line

  for(size_t i{1}; i<argc; ++i) {
    std::cout << "\targ(" << i << "): " << argv[i] << std::endl;
  } // for

} // driver

} // namespace execution
} // namespace flecsi