[Win32 API] WindowProc

An application-defined function that processes messages sent to a window. the WNDPROC type define a pointer to this callback function.

Syntax

LRESULT CALLBACK WindowProc(
  __in  HWND hwnd,
  __in  UINT uMsg,
  __in  WPARAM wParam,
  __in  LPARAM lParam
);

Parameters

• hwnd : a handle to the window.
• uMsg : The message
• For list of the system-provide messages. see System-Defined Message.
• wParam : Additional message information. The contents of this parameter depend on the value of th uMsg parameter.
• lParam : Additional message information. The contents of this parameter depend on the value of th uMsg parameter.

Return Value 

The return value is the result of the message processing and depend on the message sent.

Reference : http://msdn.microsoft.com/en-us/library/ms633573(VS.85).aspx