Call this function to create a new thread.


      CWinThread* AfxBeginThread(
   AFX_THREADPROC pfnThreadProc,
   LPVOID pParam,
   int nPriority = THREAD_PRIORITY_NORMAL,
   UINT nStackSize = 0,
   DWORD dwCreateFlags = 0,
CWinThread* AfxBeginThread(
   CRuntimeClass* pThreadClass,
   int nPriority = THREAD_PRIORITY_NORMAL,
   UINT nStackSize = 0,
   DWORD dwCreateFlags = 0,


  • pfnThreadProc
    Points to the controlling function for the worker thread. Cannot be NULL. This function must be declared as follows:

    UINT __cdecl MyControllingFunction( LPVOID pParam );

  • pThreadClass
    The RUNTIME_CLASS of an object derived from CWinThread.

  • pParam
    Parameter to be passed to the controlling function as shown in the parameter to the function declaration in pfnThreadProc.

  • nPriority
    The desired priority of the thread. For a full list and description of the available priorities, see SetThreadPriority in the Windows SDK.

  • nStackSize
    Specifies the size in bytes of the stack for the new thread. If 0, the stack size defaults to the same size stack as the creating thread.

  • dwCreateFlags
    Specifies an additional flag that controls the creation of the thread. This flag can contain one of two values:

    • CREATE_SUSPENDED   Start the thread with a suspend count of one. Use CREATE_SUSPENDED if you want to initialize any member data of the CWinThread object, such as m_bAutoDelete or any members of your derived class, before the thread starts running. Once your initialization is complete, use CWinThread::ResumeThread to start the thread running. The thread will not execute until CWinThread::ResumeThread is called.

    • 0   Start the thread immediately after creation.

  • lpSecurityAttrs
    Points to a SECURITY_ATTRIBUTES structure that specifies the security attributes for the thread. If NULL, the same security attributes as the creating thread will be used. For more information on this structure, see the Windows SDK.

Return Value

Pointer to the newly created thread object, or NULL if a failure occurs.


The first form of AfxBeginThread creates a worker thread. The second form creates a thread that may serve as a user-interface thread or as a worker thread.

AfxBeginThread creates a new CWinThread object, calls its CreateThread function to start executing the thread, and returns a pointer to the thread. Checks are made throughout the procedure to make sure all objects are deallocated properly should any part of the creation fail. To end the thread, call AfxEndThread from within the thread, or return from the controlling function of the worker thread.

Multithreading must be enabled by the application; otherwise, this function will fail. For more information on enabling multithreading, refer to /MD, /MT, /LD (Use Run-Time Library) under Visual C++ Compiler Options.

For more information on AfxBeginThread, see the articles Multithreading: Creating Worker Threads and Multithreading: Creating User-Interface Threads.


See the example for CSocket::Attach.


Header: afxwin.h

See Also

MFC Macros and Globals