Actually if you want C99, then
-std=c99 would be the right option.
--pedantic does not necessarily use C99 (it accidentially does on my system, but not necessarily on all systems, and not at all times in the future). What
--pedantic does is "
reject all programs that use forbidden extensions, and some other programs that do not follow ISO C and ISO C++. For ISO C, follows the version of the ISO C standard specified by any -std option used.".
As a side note, please do note that gcc does not support C99 at all, only the corrected version from 2001 (it's still called C99, but not the same as "real" C99).
Also please be careful if you intend to:
Some users try to use -pedantic to check programs for strict ISO C conformance. They soon find that it does not do quite what they want: it finds some non-ISO practices, but not all—only those for which ISO C requires a diagnostic, and some others for which diagnostics have been added.