CreateThread and Winsock Question

[jamesbr]

I was looking at the Winsock FAQ (http://tangentsoft.net/wskfaq/) and they had an example for a simple multi threaded server. I complied it and it worked fine. I then made a new project and made a threaded server class, CServer. When I compiled it the line

CreateThread(0, 0, EchoHandler, (void*)sd, 0, &nThreadID);

generated the error

error C2664: 'CreateThread' : cannot convert parameter 3 from 'unsigned long (void *)' to 'unsigned long (__stdcall *)(void *)'
None of the functions with this name in scope match the target type


the prototype for the function is
DWORD WINAPI CServer::EchoHandler(void* sd_)

its the exact same as in the example except for the 'CServer::' does anyone have any ideas why this won't work? Thanks in advance
James

[j0nas]

You can't pass a C++ method to CreateThread. You need to do something like this:

void CServer::Something()
{
    ...
    CreateThread(0, 0, ::EchoHandler, (void*)this, 0, &nThreadID);
    ...
}

DWORD WINAPI CServer::EchoHandler()
{
   // do your stuff here
} 


// Wrapper function
DWORD WINAPI EchoHandler(void *classPtr)
{
    CServer *server = (CServer *)classPtr;
     
    return server->EchoHandler();
}

[kuphryn]

There are several solution. Before we explore one solution, I recommend that you use _beginthreadex() instead of CreateThread(). _beginthreadex() from C/C++ run-time library cleans up memory after you use any functions from the library.

Here is one solution.

unsigned _stdcall CServer::EchoHandler();

struct EchoParam
{
// Whatever you want to pass in the callback function.
};

DWORD threadID = 0;
EchoParam *ptp = new EchoParam;
...

HANDLE hThread = reinterpret_cast<HANDLE>(
_beginthreadex(// Default security
                           NULL,
                           0,
                          // Callback function
                          EchoHandler,
                          // Callback function paramater.
                          reinterpret_cast<void *>(ptp),
                          // Initial flags
                          0,
                          // Thread ID
                          &threadID));

Kuphryn

[Andreas Masur]

Originally posted by jamesbr
CreateThread(0, 0, EchoHandler, (void*)sd, 0, &nThreadID);

generated the error

error C2664: 'CreateThread' : cannot convert parameter 3 from 'unsigned long (void *)' to 'unsigned long (__stdcall *)(void *)'
None of the functions with this name in scope match the target type

It looks like 'EchoHandler()' is a member function of your class. In this case it needs to be static in order to be used as a thread function. Further explanation can be found in the FAQ...