COMPAT(5)						      BSD File Formats Manual							 COMPAT(5)

NAME

     compat -- manipulate compatibility settings

SYNOPSIS

     COMMAND_MODE=legacy|unix2003

     #define _POSIX_C_SOURCE
     #define _DARWIN_C_SOURCE
     #define _NONSTD_SOURCE
     defined(__LP64__)

     #include <sys/cdefs.h>
     defined(_DARWIN_FEATURE_UNIX_CONFORMANCE)

DESCRIPTION

     Setting the environment variable COMMAND_MODE to the value legacy causes utility programs to behave as closely to Mac OS X 10.3's utility
     programs as possible.  When in this mode all of 10.3's flags are accepted, and in some cases extra flags are accepted, but no flags that were
     used in 10.3 will have been removed or changed in meaning.  Any behavioral changes in this mode are documented in the LEGACY sections of the
     individual utilities.

     Setting the environment variable COMMAND_MODE to the value unix2003 causes utility programs to obey the Version 3 of the Single UNIX
     Specification (``SUSv3'') standards even if doing so would alter the behavior of flags used in 10.3.

     The value of COMMAND_MODE is case insensitive and if it is unset or set to something other than legacy or unix2003 it behaves as if it were
     set to unix2003.

COMPILATION

     Defining _NONSTD_SOURCE for i386 causes library and kernel calls to behave as closely to Mac OS X 10.3's library and kernel calls as possi-
     ble.  Any behavioral changes are documented in the LEGACY sections of the man pages for the individual function calls.  Defining this macro
     when compiling for any other architecture will result in a compilation error.

     Defining _POSIX_C_SOURCE or _DARWIN_C_SOURCE causes library and kernel calls to conform to the SUSv3 standards even if doing so would alter
     the behavior of functions used in 10.3.  Defining _POSIX_C_SOURCE also removes functions, types, and other interfaces that are not part of
     SUSv3 from the normal C namespace, unless _DARWIN_C_SOURCE is also defined (i.e., _DARWIN_C_SOURCE is _POSIX_C_SOURCE with non-POSIX exten-
     sions).  In any of these cases, the _DARWIN_FEATURE_UNIX_CONFORMANCE feature macro will be defined to the SUS conformance level (it is unde-
     fined otherwise).

     Starting in Mac OS X 10.5, if none of the macros _NONSTD_SOURCE, _POSIX_C_SOURCE or _DARWIN_C_SOURCE are defined, and the environment vari-
     able MACOSX_DEPLOYMENT_TARGET is either undefined or set to 10.5 or greater (or equivalently, the gcc(1) option -mmacosx-version-min is
     either not specified or set to 10.5 or greater), then UNIX conformance will be on by default, and non-POSIX extensions will also be available
     (this is the equivalent of defining _DARWIN_C_SOURCE).  For version values less that 10.5, UNIX conformance will be off when targeting i386
     (the equivalent of defining _NONSTD_SOURCE).

     In order to provide both legacy and conformance versions of functions, two versions of affected functions are provided.  Legacy variants have
     symbol names with no suffix in order to maintain ABI compatibility.  Conformance versions have a $UNIX2003 suffix appended to their symbol
     name.  These $UNIX2003 suffixes are automatically appended by the compiler tool-chain and should not be used directly.

     Platforms that were released after these updates only have conformance variants available and do not have a $UNIX2003 suffix.

								       i386
				      ------------------------------+--------------------------------------------
					user defines	 deployment | namespace      conformance	suffix
							   target   |
				      ------------------------------+--------------------------------------------
				      (none)		   < 10.5   |	full	  10.3 compatibility	(none)
				      (none)		  >= 10.5   |	full	  SUSv3 conformance    $UNIX2003
				      _NONSTD_SOURCE	   (any)    |	full	  10.3 compatibility	(none)
				      _DARWIN_C_SOURCE	   < 10.4   |	full	  10.3 compatibility	(none)
				      _DARWIN_C_SOURCE	  >= 10.4   |	full	  SUSv3 conformance    $UNIX2003
				      _POSIX_C_SOURCE	   < 10.4   |  strict	  10.3 compatibility	(none)
				      _POSIX_C_SOURCE	  >= 10.4   |  strict	  SUSv3 conformance    $UNIX2003
				      ------------------------------+--------------------------------------------

							       Newer Architectures
				      ------------------------------+--------------------------------------------
					user defines	 deployment | namespace      conformance	suffix
							   target   |
				      ------------------------------+--------------------------------------------
				      (none)		   (any)    |	full	  SUSv3 conformance	(none)
				      _NONSTD_SOURCE	   (any)    |		       (error)
				      _DARWIN_C_SOURCE	   (any)    |	full	  SUSv3 conformance	(none)
				      _POSIX_C_SOURCE	   (any)    |  strict	  SUSv3 conformance	(none)
				      ------------------------------+--------------------------------------------

STANDARDS

     With COMMAND_MODE set to anything other than legacy, utility functions conform to Version 3 of the Single UNIX Specification (``SUSv3'').

     With _POSIX_C_SOURCE or _DARWIN_C_SOURCE for i386, or when building for any other architecture, system and library calls conform to Version 3
     of the Single UNIX Specification (``SUSv3'').

BUGS

     Different parts of a program can be compiled with different compatibility settings.  The resultant program will normally work as expected,
     for example a regex created by the SUSv3 regcomp(3) can be passed to the legacy regfree(3) with no unexpected results.  Some cases are less
     clear cut, for example what does the programmer intend when they use the SUSv3 regcomp(3) to compile a regex, but the legacy regexec(3) to
     execute it?  Any interpretation will surprise someone.

Darwin								   June 30, 2010							    Darwin