Question

First… I have the following code in a file named core_ns.h

/*
 * the prototype for the function that will be called when a connection
 * is made to a listen connection.  
 * Arguments:
 *    Server_Connection - ID of the listen connection that received the request
 *    New_Connection    - ID of the data connection that was created.
 */
typedef void (* CORE_NS_Connect_Callback)
                (CORE_NS_Connection_Type  Server_Connection,
                 CORE_NS_Connection_Type  New_Connection);

I then have the following in a file named ParameterServerCSC.h

class ParameterServer{
public:
    //-------------------------------------------------------------------------------
    //FUNCTION: sendCallback
    //
    //PURPOSE: This method will be performed upon a connection with the client. The 
    //Display Parameter Server will be sent following a connection.
    //-------------------------------------------------------------------------------
    void sendCallback (CORE_NS_Connection_Type serverConnection, CORE_NS_Connection_Type newConnection);
}; // end class ParameterServer

Finally… I have the following usage in a file named ParameterServer.cpp

       //-------------------------------------------------------------------------------
      //FUNCTION: setup 
      //
      //PURPOSE: This method will perform any initialization that needs to be performed
      //at startup, such as initialization and registration of the server. 
      //-------------------------------------------------------------------------------
      void ParameterServer::setup(bool isCopilotMfd){

            CORE_NS_Connect_Callback newConnCallback; 
            newConnCallback = &ParameterServer::sendCallback;//point to local function to handle established connection.
      }

I’m getting the following warning:

warning: converting from void (ParameterServer::*)(CORE_NS_Connection_Type, CORE_NS_Connection_Type)' tovoid (*)(CORE_NS_Connection_Type, CORE_NS_Connection_Type)’
MY_PROJECT/DisplayParameterServer
ParameterServerCSC.cpp

Im using LynxOS178-2.2.2/GCC C++ compilier. My solution builds with this warning. I am trying to understand the meaning of the warnings. Any insight to this is appreciated.

Answer 1

ParameterServer::sendCallback is a member function or method (its type is void (ParameterServer::*)(CORE_NS_Connection_Type, CORE_NS_Connection_Type)) so it cannot be used as a function (type void (*)(CORE_NS_Connection_Type, CORE_NS_Connection_Type)).

You need to make it a static member function:

static void sendCallback (CORE_NS_Connection_Type serverConnection, CORE_NS_Connection_Type newConnection);

Otherwise (depending on calling convention) when the API calls sendCallback the parameters will be set up incorrectly and will appear incorrect; at the very least the hidden this parameter will be garbage.