Example of ZMQ_PUB with HWM not working.

/**
 * Example of ZMQ_PUB with HWM not working.
 *
 * clang++ -std=c++17 -O3 pubhwm_test.cpp -o pubhwm_test -lzmq
 */

#include <zmq.hpp>
#include <iostream>
#include <chrono>
#include <thread>
#include <cstring>

int main(void)
{
    std::cout << "Starting PUB\n";
    auto const context = zmq_ctx_new();
    assert(nullptr != context);
    auto const socket = zmq_socket(context, ZMQ_PUB);
    assert(nullptr != socket);

    auto send_hwm = 100;
    {
        auto const rc = zmq_setsockopt(socket, ZMQ_SNDHWM, &send_hwm, sizeof(send_hwm));
        assert(0 == rc);
    }
    {
        auto const rc = zmq_bind(socket, "ipc:///tmp//zmq_ipc_example");
        assert(0 == rc);
    }

    char* end = nullptr;
    char msg[] = "Never say never again.";
    auto const len = strlen(msg);
    for (long i = 0; ; ++i) {
        auto const rc = zmq_send(socket, msg, len, ZMQ_DONTWAIT);
        if (-1 == rc) {
            std::cerr << "Failure sending message number=" << i << std::endl;
        } else {
            std::cout << "Send message number=" << i << std::endl;
        }
        std::this_thread::sleep_for(std::chrono::milliseconds(20));
    }
    zmq_close(socket);
    zmq_ctx_destroy(context);
    return EXIT_SUCCESS;
}