"expected ';' at the end of declaration list" error for zeromq

Question

I am using Mac, and i use homebrew to install zeromq. I want to use zeromq for my application. I tried to compile zmq.hpp https://github.com/zeromq/cppzmq/blob/master/zmq.hpp with

int main () {
    //  Prepare our context and socket
    zmq::context_t context (1);
    zmq::socket_t socket (context, ZMQ_REP);
    socket.bind ("tcp://*:5555");

    while (true) {
        zmq::message_t request;

        //  Wait for next request from client
        socket.recv (&request);
        std::cout << "Received Hello" << std::endl;

        //  Do some 'work'
        sleep (1);

        //  Send reply back to client
        zmq::message_t reply (5);
        memcpy ((void *) reply.data (), "World", 5);
        socket.send (reply);
    }
    return 0;
}

but it failed. The error shows

"frameworks/zmq/zmq.hpp:377:35: error: expected ';' at end of declaration list socket_t (const socket_t&) ZMQ_DELETED_FUNCTION; ^ ; frameworks/zmq/zmq.hpp:379:42: error: expected ';' at end of declaration list void operator = (const socket_t&) ZMQ_DELETED_FUNCTION;"

Why is this happened? The zmq.hpp code does not contain any errors. Please help.

Finally I do this and it worked.

#if __has_feature(cxx_deleted_functions)
        #define ZMQ_DELETED_FUNCTION = delete
    #else
        #define ZMQ_DELETED_FUNCTION
    #endif

Thanks a lot. Audrey.

Answer 1

The macro ZMQ_DELETED_FUNCTION was apparently introduced to provide conditional support for such C++11 feature as "deleted functions" (= delete). Your compiler does not seem to support that C++11 feature. Hence the error.

By design, the zmq.hpp attempts to set this macro automatically, by analyzing the compiler version and defining the macro accordingly. It is possible that this automatic detection is being too optimistic. However, it is also possible that your compiler actually supports that feature, you just forgot to turn it on in the compiler settings.

BTW, I'm looking at the Clang section of the code that defines the macro

  #elif defined(__clang__)
    #if __has_feature(cxx_rvalue_references)
        #define ZMQ_HAS_RVALUE_REFS
    #endif

    #if __has_feature(cxx_deleted_functions)
        #define ZMQ_DELETED_FUNCTION = delete
    #endif

and it looks broken to me. If the compiler does not support cxx_deleted_functions feature, then macro ZMQ_DELETED_FUNCTION remains undefined (instead of being defined as empty). This is wrong.

Are you using Clang? If so, this could actually be the reason for your error. In that case the error can be fixed by pre-defining ZMQ_DELETED_FUNCTION as an empty macro, either as a global macro definition or in the source code before including zmq.hpp.