Windows Subsystem

Windows kernel or ntoskrnl.exe binary is the lowest level of Windows OS. Application / user layer starts from system call library named as ntdll.dll. This DLL implements the lowest level system call for Windows. Above it there are win32 DLLs. Major Win32 DLLs are kernel32.dll, user32.dll, gdi32.dll etc. These DLLs provides API wrappers to the application. These are very well known as Win32 API libraries. Above this layer programming language runtime libraries are residing. Like for example if application was written with VC++. The runtime will be msvcrt.dll. Finally above it application runs.

  • Application: Application .EXE
  • language runtime: msvcrt.dll
  • Win32 DLLs: Kernel32.dll, User32.dll, Gdi32.dll
  • System DLL: Ntdll.dll
  • Windows OS: NtOsKrnl.EXE + hal.dll

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Further readings

Where is WinMain() function in MFC application ?

MFC hides WinMain in its framework and includes source file on WinMain(). This explains how framework calls global CWinApp::Initinstance() from entry WinMain.

What is the utility of CWinApp class?

This is constructed during global C++ objects are constructed and is already available when Windows calls the WinMain function, which is supplied by the ...

Basic steps in Win32 GUI Application with source code.

Define a custom Window class structure, Register the class name, CreateWindow, Show windows and write message get and dispatch loop statements. Define the Window CallBack procedure and write the handlers.

What is a Window CallBack procedure and what is its utility?

DispatchMessage() is a API which indirectly triggers the Window CallBack procedure. Message structure members from this function are passed to the CallBack procedure. CallBack procedure should implement event handlers depending on the need of the application.

What are LPARAM and WPARAM in window proc function?

LPARAM and WPARAM are the two parameters in Window CallBack procedure. They signifies parameters of various events. They are used in handing individual events.

What are the basic steps of a typical MFC based application?

We need to write WinMain and need to follow all these in a Win32 application. However we need not to write much if we are writing an application with MFC ...