## BUG: Incorrect C4050 Warning When Using Function Pointers

Q110717

    7.00   | 1.00 1.50
    MS-DOS | WINDOWS
    kbtool kbbuglist

    ----------------------------------------------------------------------
    The information in this article applies to:

     - The Microsoft C/C++ Compiler (CL.EXE), included with:

        - Microsoft C/C++ for MS-DOS, versions 7.0
        - Microsoft Visual C++ for Windows, versions 1.0 and 1.5
    ----------------------------------------------------------------------

    SYMPTOMS
    ========

    Attempting to assign the address of a function marked as __loadds or
    __export to a correctly declared function pointer will cause the
    compiler to incorrectly generate a C4050 warning when the following
    conditions are true:

     - The code being compiled is in a .C file
     - Warning level 4 of the compiler is being used

    The complete C4050 warning message generated is:

       warning C4050: 'argument' : different code attributes

    The sample code shown below illustrates this problem.

    RESOLUTION
    ==========

    To avoid the C4050 warning, use one of the following methods:

     - Provide a cast when assigning the address of the function to the
       function pointer

       -or-

     - Compile at warning level 3 with the /W3 compiler switch

       -or-

     - Disable the C4050 warning with the following #pragma warning
       directive:

       #pragma warning ( disable: 4050 )

    STATUS
    ======

    Microsoft has confirmed this to be a bug in the products listed at the
    beginning of this article. We are researching this bug and will post new
    information here in the Microsoft Knowledge Base as it becomes available.

    This is not a problem in the 32-bit compiler.

    MORE INFORMATION
    ================

    NOTE: The C4050 warning message is not generated when code matching
    the scenario listed above is located in a .CPP file.

    Sample Code
    -----------

    /* Compile options needed: /W4 /c
    *
    *  Compile this sample code as a .C file
    */

    #include <windows.h>

    void Function();

    int FAR PASCAL __loadds CallbackProc1(int i) { return i; }
    typedef int (FAR PASCAL __loadds *FNPROC1)(int);

    int FAR PASCAL __export CallbackProc2(int i) { return i; }
    typedef int (FAR PASCAL __export *FNPROC2)(int);

    /* Uncomment the following line to disable the C4050 warning
    */

    /*
    #pragma warning ( disable: 4050 )
    */

    void Function()
    {
      /* Function pointer variables */
      int (FAR PASCAL *lpfnProc1)(int);
      int (FAR PASCAL __export *lpfnProc2)(int);

      lpfnProc1 = CallbackProc1;          /* This line generates C4050 */
      lpfnProc1 = (FNPROC1)CallbackProc1; /* No warning on this line   */

      lpfnProc2 = CallbackProc2;          /* This line generates C4050 */
      lpfnProc2 = (FNPROC2)CallbackProc2; /* No warning on this line   */
    }

    Additional reference words: 1.00 1.50 7.00 8.00 8.00c
    KBCategory: kbtool kbbuglist
    KBSubcategory: CLIss

Keywords : kb16bitonly
Issue type : kbbug
Technology : kbVCsearch kbAudDeveloper kbCVCComp

Last Reviewed: May 5, 2001 © 2001 Microsoft Corporation. All rights reserved. Terms of Use.