???????????ж???????POSIX.1??XSI?????????????POSIX.1??XSI????????????????????Щ????????????????????????塣???????????????????????????POSIX???????????κ??????????????????????????峣??_POSIX_C_SOURCE??????POSIX.1?????ж????????????????ó????????????κ??????е???塣
???????POSIX.1?????????汾????????_POSIX_SOURCE????????POSIX.1??2001???У??????滻?_POSIX_C_SOURCE??
????????_POSIX_C_SOURCE??_XOPEN_SOURCE??????????????feature test macro???????й????????????????????????????????????cc?????????????з?????壺
????cc -D_POSIX_C_SOURCE=200112 file.c
?????????C????????κ???????????????????????????????????POSIX.1???壬????????????????????????
????#define _POSIX_C_SOURCE 200112
??????Single UNIX Specification v3??????????ó????????軔????_XOPEN_SOURCE?????600??
????Single UNIX Specification??c99??ó??????C?????????????????????????·???????????
????c99 -D_XOPEN_SOURCE=600 file.c -o file
?????????gcc C????????????1999 ISO C????????????-std = c99????????????
????gcc -D_XOPEN_SOURCE=600 -std=c99 file.c -o file
????????????????????__STDC__?????????ISO C?????C????????????塣?????????????дISO C?????????ISO C????????????????????磬???????ISO C????????????????????????????????
#ifdef __STDC__
void *myfunc( const char *?? int );
#else
void *myfunc();
#endif
??????????????????C???????????ISO C???????????????????????__STDC__????????