How to detect Operating System through a C program

One can find out the operating system on which the program is running with the help of C programming. This piece of information is very useful for the case where we want to build platform independent program. To find the OS (Operating System) we check out the macro defined by the compiler, for example windows with 32-bit OS has "_WIN32" as macro so if the macro is defined then the system we are working on is windows with 32-bit operating system. Similarly other OS has different macro defined. The list of macro for some popular OS are as follows:

Sr. No.	Operating System	Macro Present	Notes
1.	Windows 32-bit + 64-bit	_WIN32	for all Windows OS
2.	Windows 64 bit	_WIN64	Only for 64 bit windows
3.	Apple	__APPLE__	For all Apple OS
4.	Apple	__MACH__	alternative to above
5.	iOS embedded	TARGET_OS_EMBEDDED	include TargetConditionals.h
6.	iOS simulator	TARGET_IPHONE_SIMULATOR	include TargetConditionals.h
7.	iPhone	TARGET_OS_IPHONE	include TargetConditionals.h
8.	MacOS	TARGET_OS_MAC	include TargetConditionals.h
9.	Android	__ANDROID__	subset of linux
10.	Unix based OS	__unix__	-
11.	Linux	__linux__	subset of unix
12.	POSIX based	_POSIX_VERSION	Windows with Cygwin
13.	Solaris	__sun	-
14.	HP UX	__hpux	-
15.	BSD	BSD	all BSD flavors
16.	DragonFly BSD	__DragonFly__	-
17.	FreeBSD	__FreeBSD__	-
18.	NetBSD	__NetBSD__	-
19.	OpenBSD	__OpenBSD__	-

Note:

It must be noted that the macros are valid for GNU GCC and G++ and may vary for other compilers.

Below is the program to detect which OS we are working on: Output: Below is the output of the above program on a Windows OS: 👁 Image
Similarly one can find out the operating system and can