There are a number of child header files that are automatically included with windows.h. Many of these files cannot simply be included by themselves (they are not self-contained), because of dependencies.

windows.h may include any of the following header files:

• stdarg.h – variable-argument functions (standard C header)
• windef.h – various macros and types
• winnt.h – various macros and types (for Windows NT) [1]
• basetsd.h – various types [2]
• guiddef.h – the GUID type [3]
• ctype.h – character classification (standard C header)
• string.h – strings and buffers (standard C header)
• winbase.h – kernel32.dll: kernel services; advapi32.dll:kernel services(e.g. CreateProcessAsUser function), access control(e.g. AdjustTokenGroups function).
• winerror.h – Windows error codes [4]
• wingdi.h – GDI (Graphics Device Interface) [5]
• winuser.h – user32.dll: user services, inline resource macro(e.g. MAKEINTRESOURCE macro [6]), inline dialog macro(e.g. DialogBox function [7]). [8]
• winnls.h – NLS (Native Language Support)
• wincon.h – console services
• winver.h – version information [9]
• winreg.h – Windows registry [10]
• winnetwk.h – WNet (Windows Networking) [11]
• winsvc.h – Windows services and the SCM (Service Control Manager)
• imm.h – IME (Input Method Editor)

Extra includes edit

• cderr.h – CommDlgExtendedError function error codes
• commdlg.h – Common Dialog Boxes
• dde.h – DDE (Dynamic Data Exchange)
• ddeml.h – DDE Management Library
• dlgs.h – various constants for Common Dialog Boxes
• lzexpand.h – LZ (Lempel-Ziv) compression/decompression
• mmsystem.h – Windows Multimedia
• nb30.h – NetBIOS
• rpc.h – RPC (Remote procedure call)
• shellapi.h – Windows Shell API
• wincrypt.h – Cryptographic API
• winperf.h – Performance monitoring
• winresrc.h – used in resources
• winsock.h – Winsock (Windows Sockets), version 1.1
• winspool.h – Print Spooler
• winbgim.h – Standard graphics library

OLE and COM edit

• ole2.h – OLE (Object Linking and Embedding)
• objbase.h – COM (Component Object Model)
• oleauto.h – OLE Automation
• olectlid.h – various GUID definitions

Several macros affect the behavior of windows.h.

• UNICODE – when defined, this causes TCHAR to be a synonym of WCHAR instead of CHAR[12], and all type-generic API functions and messages that work with text will be defined to the -W versions instead of the -A versions. (It is similar to the windows C runtime's _UNICODE macro.)
• RC_INVOKED – defined when the resource compiler (RC.EXE) is in use instead of a C compiler.
• WINVER – used to enable features only available in newer operating systems. Define it to 0x0501 for Windows XP, and 0x0600 for Windows Vista.
• WIN32_LEAN_AND_MEAN – used to reduce the size of the header files and speed up compilation. Excludes things like cryptography, DDE, RPC, the Windows Shell and Winsock.

• Windows.pas