Example: serialization_variant_example

C++ example source code:

/* +------------------------------------------------------------------------+
   |                     Mobile Robot Programming Toolkit (MRPT)            |
   |                          https://www.mrpt.org/                         |
   |                                                                        |
   | Copyright (c) 2005-2024, Individual contributors, see AUTHORS file     |
   | See: https://www.mrpt.org/Authors - All rights reserved.               |
   | Released under BSD License. See: https://www.mrpt.org/License          |
   +------------------------------------------------------------------------+ */

#include <mrpt/io/CPipe.h>
#include <mrpt/poses/CPose2D.h>
#include <mrpt/poses/CPose3D.h>
#include <mrpt/serialization/CArchive.h>

#include <chrono>
#include <iostream>
#include <thread>

using namespace mrpt;
using namespace mrpt::poses;
using namespace mrpt::system;
using namespace mrpt::io;
using namespace mrpt::serialization;
using namespace std;

void thread_reader(CPipeReadEndPoint& read_pipe)
{
  try
  {
    std::cout << "[thread_reader ID:" << std::this_thread::get_id() << "] Started." << std::endl;

    // Simple read commands:
    size_t len = 0;
    char buf[100];
    read_pipe.Read(&len, sizeof(len));
    read_pipe.Read(buf, len);
    buf[len] = 0;
    cout << "RX: " << buf << endl;

    // Read MRPT object from a pipe:
    // *Note*: If the object class is known in advance, one can avoid smart
    // pointers with ReadObject(&existingObj)
    auto arch = archiveFrom(read_pipe);
#if !defined(HAS_BROKEN_CLANG_STD_VISIT)
    auto doprint = [](auto& pose) { cout << "RX pose: " << pose << endl; };
    auto var = arch.ReadVariant<mrpt::poses::CPose2D, mrpt::poses::CPose3D>();
    std::visit(doprint, var);
    var = arch.ReadVariant<mrpt::poses::CPose2D, mrpt::poses::CPose3D>();
    std::visit(doprint, var);
#else
    std::cout << "Code disabled for clang due to variant bug. See: "
                 "https://stackoverflow.com/a/46507150/1631514\n";
#endif

    printf("[thread_reader] Finished.\n");
  }
  catch (const std::exception& e)
  {
    cerr << e.what() << endl;
  }
}

void thread_writer(CPipeWriteEndPoint& write_pipe)
{
  try
  {
    std::cout << "[thread_writer ID:" << std::this_thread::get_id() << "] Started." << std::endl;

    // Simple write commands:
    const char* str = "Hello world!";
    size_t len = strlen(str);
    write_pipe.Write(&len, sizeof(len));
    write_pipe.Write(str, len);

    // Send MRPT objects:
    mrpt::poses::CPose3D pose1(1, 2, 3, 1.57, 3.14, 0);
    mrpt::poses::CPose2D pose2(1.0, 2.0, 3.1415);

#if !defined(HAS_BROKEN_CLANG_STD_VISIT)
    std::variant<mrpt::poses::CPose3D, mrpt::poses::CPose2D> var1(std::move(pose1));
    std::variant<mrpt::poses::CPose3D, mrpt::poses::CPose2D> var2(std::move(pose2));
    auto arch = archiveFrom(write_pipe);
    arch.WriteVariant(var1);
    arch.WriteVariant(var2);
#endif
    printf("[thread_writer] Finished.\n");
  }
  catch (const std::exception& e)
  {
    cerr << e.what() << endl;
  }
}

// ------------------------------------------------------
//              ThreadsTest
// ------------------------------------------------------
void ThreadsTest()
{
  // Create a pipe:
  std::unique_ptr<CPipeReadEndPoint> read_pipe;
  std::unique_ptr<CPipeWriteEndPoint> write_pipe;

  CPipe::createPipe(read_pipe, write_pipe);

  // And send the two end-points to two threads:
  std::thread hT1(thread_reader, std::ref(*read_pipe));
  std::thread hT2(thread_writer, std::ref(*write_pipe));

  using namespace std::chrono_literals;
  std::this_thread::sleep_for(10ms);
  // Wait for the threads to end.
  hT2.join();
  // We need to close this to ensure the pipe gets flushed
  // Remember Unix uses buffered io
  // write_pipe.reset();
  hT1.join();
}

// ------------------------------------------------------
//                      MAIN
// ------------------------------------------------------
int main()
{
  try
  {
    ThreadsTest();

    return 0;
  }
  catch (const std::exception& e)
  {
    std::cerr << "MRPT error: " << mrpt::exception_to_str(e) << std::endl;
    return -1;
  }
}