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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 possible.  Any behavioral changes are documented in the LEGACY sec-tions sections
     tions 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 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 func-tions functions
     tions are provided.  Legacy variants have symbol names with no suffix in order to maintain ABI compati-bility. compatibility.
     bility.  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 ------------------------------+-------------------------------------------user
                     user defines     deployment | namespace      conformance        suffix
                                        target   |
                   ------------------------------+--------------------------------------------(none) ------------------------------+-------------------------------------------(none)
                   (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 ------------------------------+-------------------------------------------Newer
                                              Newer Architectures
                   ------------------------------+--------------------------------------------user ------------------------------+-------------------------------------------user
                     user defines     deployment | namespace      conformance        suffix
                                        target   |
                   ------------------------------+--------------------------------------------(none) ------------------------------+-------------------------------------------(none)
                   (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 ------------------------------+-------------------------------------------STANDARDS

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 pro-gram program
     gram 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

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