http://gcc.gnu.org/bugzilla/show_bug.cgi?id=40411
--- Comment #19 from Jonathan Wakely <redi at gcc dot gnu.org> 2010-12-26 21:52:07 UTC --- (In reply to comment #17) > For this reason, I would find it bad if "gcc -std=c99" or "gcc -std=gnu99" > would cause values-xpg6.o to be included in the link. Please close this > issue as "Won't fix". Programs which wish to have POSIX compliant behaviour > of system functions can use GNU gnulib; it doesn't rely on values-xpg6.o. I don't entirely agree with this line of reasoning. If the system provides a POSIX compliant C library it's reasonable to want to use it and users will want some way to tel the compiler to do so. Whether using it is enabled via -std or not, linking to values-xpg6.o can cause unexpected behaviour for applications or shared objects. It does seem reasonable to expect -std=c99 to enable C99 features if the system supports them, and similarly for -std=c++0x