Example: serialization_variant_example

C++ example source code:

/* +------------------------------------------------------------------------+
   |                     Mobile Robot Programming Toolkit (MRPT)            |
   |                          https://www.mrpt.org/                         |
   |                                                                        |
   | Copyright (c) 2005-2023, 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;
    }
}