Using 'true' C99 is a bad idea, because the headers of many libraries don't work if you use -std=c11. gcc's default has always been the 'gnu' variant, so previ

Using 'true' C99 is a bad idea, because the headers of many libraries don't work if you use -std=c11. gcc's default has always been the 'gnu' variant, so previously gnu90, now gnu99. I has similar problems when I switched from the default (at the time) C++03 to -std=c++11 and found unexpected things broke. I switched to -std=gnu++11 and everything was fine.