According to GCC reference, C17 is actually a bug-fix version of the C11 standard with DR resolutions integrated.

C17, a bug-fix version of the C11 standard with DR [Defect Report] resolutions integrated, will soon go to ballot. This patch adds corresponding options -std=c17 , -std=gnu17 (new default version, replacing -std=gnu11 as the default), -std=iso9899:2017 . As a bug-fix version of the standard, there is no need for flag_isoc17 or any options for compatibility warnings; however, there is a new __STDC_VERSION__ value, so new cpplib languages CLK_GNUC17 and CLK_STDC17 are added to support using that new value with the new options. (If the standard ends up being published in 2018 and being known as C18 , option aliases can be added. Note however that -std=iso9899:199409 corresponds to a __STDC_VERSION__ value rather than a publication date.)

(There are a couple of DR resolutions needing implementing in GCC, but that's independent of the new options.)