AMQP-CPP 初学者问题

Question

I'm new to rabbitmq, and try to have a Listener to read from a messagequeue. The server should be fine (not implemented by me, I guess implemented in Java). I use C++ for the consumer, and I use the amqpcpp library.

This is what I tried until now:

    int main(int argc, char* const argv[])
{
  // access to the boost asio handler
    // note: we suggest use of 2 threads - normally one is fin (we are simply demonstrating thread safety).
    boost::asio::io_service service(2);

    // handler for libev
    AMQP::LibBoostAsioHandler handler(service);
    
    // make a connection
    AMQP::Address address("amqp://10.40.216.87");
    AMQP::TcpConnection connection(&handler, address);

    // we need a channel too
    AMQP::TcpChannel channel(&connection);


    //channel.onError(errorTCP);

    channel.declareQueue("logmessages");

   // Define callbacks and start
    auto messageCb = [&channel](
            const AMQP::Message &message, uint64_t deliveryTag, 
            bool redelivered)
    {
        std::cout << "message received" << std::endl;
        // acknowledge the message
        // channel.ack(deliveryTag);
        //processMessage(message.routingKey(), message.body());
    };

    // callback function that is called when the consume operation starts
    auto startCb = [](const std::string &consumertag) {

        std::cout << "consume operation started: " << consumertag << std::endl;
    };

    // callback function that is called when the consume operation failed
    auto errorCb = [](const char* message) {

        std::cout << "consume operation failed:" << *message << std::endl;
    };

    channel.consume("logmessages")
        .onReceived(messageCb)
        .onSuccess(startCb)
        .onError(errorCb);

    
    // create a temporary queue
    /*channel.declareQueue(AMQP::exclusive).onSuccess([&connection](const std::string &name, uint32_t messagecount, uint32_t consumercount) {
        
        // report the name of the temporary queue
        std::cout << "declared queue " << name << std::endl;
        
        // now we can close the connection
        connection.close();
    });*/

    channel.consume("devices.state.*");
    
    // run the handler
    // a t the moment, one will need SIGINT to stop.  In time, should add signal handling through boost API.
    return service.run();
}

I always get a "consume operation failed". The question is now why...Is there any way to get more error messages? (eg could not connect with TCP socket, could not find queue with correct name, etc.).

Thanks for your tips!

Answer 1

In your code, you're trying to cout the *message pointer instead of the message itself.

Instead of,

auto errorCb = [](const char* message) {
    std::cout << "consume operation failed:" << *message << std::endl;
};

It should be,

auto errorCb = [](const char* message) {
    std::cout << "consume operation failed:" << message << std::endl;
};

That should give you proper error message. Please checkout the docs/examples in the official repo .