RegisterClassEx Fails as Invalid Parameter - C++

Question

A call to RegisterClassEx in my application is failing with error code 87, "The parameter is incorrect."

memset( &m_wcx, 0, sizeof(WNDCLASSEX) );

m_wcx.cbSize = sizeof(WNDCLASSEX);  // size of structure
m_wcx.style = WS_ICONIC;            // initially minimized
m_wcx.lpfnWndProc = &WndProc;       // points to window procedure
m_wcx.cbClsExtra = 0;               // no extra class memory
m_wcx.cbWndExtra = 0;               // no extra window memory
m_wcx.hInstance = m_hInstance;      // handle to instance
m_wcx.hIcon = ::LoadIcon( NULL, IDI_APPLICATION ); // default app icon
m_wcx.hCursor = ::LoadCursor( NULL, IDC_ARROW ); // standard arrow cursor
m_wcx.hbrBackground = NULL;         // no background to paint
m_wcx.lpszMenuName = NULL;          // no menu resource
m_wcx.lpszClassName = _pwcWindowClass; // name of window class
m_wcx.hIconSm = NULL;               // search system resources for sm icon

m_atom = ::RegisterClassEx( &m_wcx );

if ( m_atom == 0 )
{
    TRACE(_T("CNotifyWindow::CNotifyWindow : Failed to register window class.\r\n\tError: %d\r\n\tFile: %s\r\n\tLine: %d\r\n"), ::GetLastError(), __WFILE__, __LINE__);
    THROW(::GetLastError());
}

Does anyone know what I'm doing wrong? Thanks.

Answer 1

The style member of the WNDCLASSEX structure accepts class styles, not window styles. In other words, you can't make all windows of that class initially minimized that way.

You should pass WS_ICONIC in the dwStyle argument to CreateWindow() or CreateWindowEx() instead.

Answer 2

Usually "The parameter is incorrect" is the WINAPI's way of saying, "dude, you're sending me crap."

So one of the WNDCLASSEX member variables is probably crap. Start by taking a closer look at the variables that are most likely to have something inappropriate in them: m_wcx.hInstance, m_wcx.lpfnWndProc, and m_wcx.lpszClassName.

EDIT:

As pointed out by @Johann Gerell, m_wcx.style = WS_ICONIC is an example of this. The documentation says that this is a class style, but you've sent a window style. No good.

What's the difference? Well, you know the difference between a C++ class and an object, right? A class is like a blueprint. An object is an instantiation of that blueprint. Same is true of Window Classes & Windows. A Window Class is a blueprint for creating a window, and a window is an instantiation of that Window Class. Window Classes have styles that specify things like what kind of DC to use, when to vertical refresh -- low level stuff like that which applies to every instance of that window class. Windows also have styles, but these are different. Window styles specify per-window things like if the window should be visible, minimized, etc. So RegisterClassEx asked you for an orange, and you tried to give it an apple.

Answer 3

The first thing is the WS_ICONIC. The window class style is something entirely diferent from window style. The class styles are the CS_* ones.