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.