getopenfilename功能没有打开对话框

所以我有一个简单的代码，因为我是Win32的新手

LRESULT CALLBACK WindowProcedure (HWND hwnd, UINT message, WPARAM wParam, LPARAM lParam)
{
    switch (message)                  /* handle the messages */
    {
        case WM_DESTROY: PostQuitMessage (0); break;
        case WM_CREATE : make_controls(hwnd); break;
        case WM_COMMAND: handle_commands(hwnd, wParam, lParam); break;
        default:                      /* for messages that we don't deal with */
            return DefWindowProc (hwnd, message, wParam, lParam);
    }
    return 0;
} 

这是handle_commands函数

void handle_commands(HWND hwnd, WPARAM wp, LPARAM lp){
    if( HIWORD(wp) == BN_CLICKED && LOWORD(wp) == openBtn ){
// openBtn is the only button in the whole application 
        OPENFILENAME ofn;       // common dialog box structure
        char szFile[260];       // buffer for file name
        HWND hwnd;              // owner window
        HANDLE hf;              // file handle
// Initialize OPENFILENAME
        ZeroMemory(&ofn, sizeof(ofn));
        ofn.lStructSize = sizeof(ofn);
        ofn.hwndOwner = hwnd;
        ofn.lpstrFile = szFile;
// Set lpstrFile[0] to '' so that GetOpenFileName does not
// use the contents of szFile to initialize itself.
        ofn.lpstrFile[0] = '';
        ofn.nMaxFile = sizeof(szFile);
        ofn.lpstrFilter = "All*.*Text*.TXT";
        ofn.nFilterIndex = 1;
        ofn.lpstrFileTitle = NULL;
        ofn.nMaxFileTitle = 0;
        ofn.lpstrInitialDir = NULL;
        ofn.Flags = OFN_PATHMUSTEXIST | OFN_FILEMUSTEXIST;
// Display the Open dialog box.
        if (GetOpenFileName(&ofn)==TRUE)
            hf = CreateFile(ofn.lpstrFile,
                            GENERIC_READ,
                            0,
                            (LPSECURITY_ATTRIBUTES) NULL,
                            OPEN_EXISTING,
                            FILE_ATTRIBUTE_NORMAL,
                            (HANDLE) NULL);
    }
}// this is the end of the handle_commands functions

但问题是它没有打开任何对话框

尽我所能，互联网上的人们成功开放了相同的代码。

是的！我包括Commdlg.h和相应的库

预先感谢！