WebJul 7, 2022 · ISO/IEC 9899:1999, a.k.a. C99, is a previous revision of the C standard. This section is incomplete Reason: core/library features, TC1~TC3, DRs : Contents. 1 Obsolete. 1.1 Removed; 1.2 Deprecated; 2 New language features. 2.1 Feature test macros for optional features; 3 New library features. 3.1 New headers;