Predefined macros in C/C++ that tell you what language features are available.

These are the predefined macros that C/C++ compilers define to tell you what language features are available. There are also predefined macros in C/C++ that tell you the compiler, predefined macros in C/C++ that tell you the target processor and predefined macros in C/C++ that tell you what language features are available.

These are most often used in library header files.

Feature	Macros for each compiler
Feature	OpenWatcom	MSVC++	IBM VAC++/ILEC++	DigitalMars	GCC
Feature	OpenWatcom	MSVC++	IBM VAC++/ILEC++	DigitalMars	GCC
Feature	Macros for each compiler
The run-time library is in a DLL (so standard library headers have to mark function declarations as imported)	`__SW_BR` is 1	`_DLL` is 1	`__IMPORTLIB__` is 1	`_DLL` is 1	(nothing)
Multiple threading support is desired in the run-time library.	`__SW_BM` is 1 and `_MT` is 1	`_MT` is 1	`__MULTI__` is 1	`_MD` is 1	`_REENTRANT` is 1
Exceptions are enabled.	`__CPPUNWIND` is 1	`_CPPUNWIND` is 1	(nothing)	`_CPPUNWIND` is 1	`__EXCEPTIONS__` is 1
Run-time type information (and thus dynamic casting) is enabled.	`__CPPRTTI` is 1	`_CPPRTTI` is 1	(nothing)	(nothing)	`__GXX_RTTI` is 1
`char` is signed.	`__SW_J` is 1 and `__CHAR_SIGNED__` is 1	(nothing)	`_CHAR_SIGNED` is 1 and `__CHAR_SIGNED__` is 1	(nothing)	(nothing)
`char` is unsigned.	(nothing)	`__CHAR_UNSIGNED__` is 1	`_CHAR_UNSIGNED` is 1 and `__CHAR_UNSIGNED__` is 1	`_CHAR_UNSIGNED` is 1	`__CHAR_UNSIGNED__` is 1
`wchar_t` is signed.	(nothing)	(nothing)	(nothing)	(nothing)	(nothing)
`wchar_t` is unsigned.	(nothing)	(nothing)	(nothing)	(nothing)	`__WCHAR_UNSIGNED__` is 1
Language extensions are available (and so can be safely used in headers).	(nothing)	`_MSC_EXTENSIONS` is 1	`__EXTENDED__` is 1	(nothing)	(nothing)
Language extensions are unavailable (and so cannot be safely used in headers).	`NO_EXT_KEYS` is 1	(nothing)	`__ANSI__` is 1	(nothing)	`__STRICT_ANSI__` is 1
Library headers may declare `inline` functions.	`__SW_OI` is 1 and `__INLINE_FUNCTIONS__` is 1	(nothing)	(nothing)	(nothing)	(nothing)
Library headers may not declare `inline` functions.	(nothing)	(nothing)	(nothing)	(nothing)	`__NO_INLINE__` is 1
Library headers may use compiler intrinsics.	`__SW_OM` is 1	(nothing)	(nothing)	(nothing)	(nothing)
Optimization for space, rather than time, is requested.	`__SW_OS` is 1	(nothing)	(nothing)	(nothing)	`__OPTIMIZE_SIZE__` is 1

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