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 utili-
     ties.

     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 extensions).
     In any of these cases, the _DARWIN_FEATURE_UNIX_CONFORMANCE feature macro
     will be defined to the SUS conformance level (it is undefined 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
     variable 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 val-
     ues 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.  Con-
     formance 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