The C compiler supports the _Restrict keyword as an equivalent to the restrict keyword in the C99 standard. The _Restrict keyword is available with any -std flag value when -pedantic is not specified, whereas the restrict keyword is only available with -std=c99 or -std=c11.
For more information about supported C11 features, see Appendix C, Features of C11.
For more information about supported C99 features, see Appendix D, Features of C99.