Basic Threads using C++

Question

I am trying to create a simple thread using c++. I am getting the error: Error 14 error C2276: '&' : illegal operation on bound member function expression

This is my code:

void PeerCommunication(PeerData &peerData, std::string infoHash)
{
    Peer peer(peerData.GetIP(), peerData.GetPort(), infoHash);
    peer.CreateConnection();
    peer.HasPeace(0);
    peer.RecievePeace(0, 4056211 + 291); 
}

TcpPeers(OrderedMap<std::string, unsigned short> peers, std::string infoHash, Bencoding bencoder)
{
    std::vector<std::thread> threads;
    //std::thread ttt[num_threads];
    //std::thread t1(task1, "Hello");
    for (std::size_t i = 0; i < peers.GetSize(); i++)
    {
        PeerData pd(peers.GetKeyByIndex(i), peers.GetValueByIndex(i));
        std::thread t(&PeerCommunication, pd, infoHash);
        threads.push_back(t);
    }

    for (std::size_t i = 0; i < peers.GetSize(); i++)
    {
        threads.at(i).join();
    }
    ...
  }

I have tried to remove the reference: std::thread t(PeerCommunication, pd, infoHash); and it still doesn't works.

When I do it (remove the refernce) the error is: Error 4 error C3867: 'TcpPeers::PeerCommunication': function call missing argument list; use '&TcpPeers::PeerCommunication' to create a pointer to member

*I have tried to remove the reference: `std::thread t(PeerCommunication, pd, infoHash);` and it still doesn't works.* Can you elaborate on that? — NathanOliver, Jan 07 '16 at 17:58
What do you mean by "it still doesn't work"? Did you get another error? Result differ from your expectations? — Algirdas Preidžius, Jan 07 '16 at 17:58
Do, by any chance, your functions belong to a class (and are class methods), which your example does not reflect? — Algirdas Preidžius, Jan 07 '16 at 18:03
Your `TcpPeers()` function doesn't have a return type. And your `PeerCommunication()` function doesn't return anything. — Galik, Jan 07 '16 at 18:03
@AlgirdasPreidžius both functions are in the same class called "TcpPeers" — , Jan 07 '16 at 18:04
Why not just: std::thread t(PeerCommunication, pd, infoHash); — George Houpis, Jan 07 '16 at 18:06
@GeorgeHoupis as I said in my question, I tried it, and it still give an error (the error is not the same) — , Jan 07 '16 at 18:07
The ampersand in `&PeerCommunication` does not mean "reference", it means "address of". — molbdnilo, Jan 07 '16 at 18:09
And were you expecting to pass two parameters to your PeerCommunication method because it is defined with only one? — George Houpis, Jan 07 '16 at 18:14
@GeorgeHoupis Sorry, accidently I did it, but it still gave the same error in both cases. I edited my question again. — , Jan 07 '16 at 18:16
Because PeerCommunication is a class method, you have to pass 'this' as the first parameter. Try std::thread t(&PeerCommunication, this, pd, infoHash); — George Houpis, Jan 07 '16 at 18:19

Galik · Accepted Answer · 2016-01-07T18:33:59.653

You need to return something from your PeerCommunication() function.

I suspect you want something a little more like this:

for (std::size_t i = 0; i < peers.GetSize(); i++)
{
    PeerData pd(peers.GetKeyByIndex(i), peers.GetValueByIndex(i));

    // Use emplace as std::thread non-copyable
    // Pass this pointer with member functions
    // Use std::ref to pass references
    threads.emplace_back(&TcpPeers::PeerCommunication, this, std::ref(pd), infoHash);
}

for (std::size_t i = 0; i < peers.GetSize(); i++)
{
    threads.at(i).join();
}

Basic Threads using C++

1 Answers1