#assert: Obsolete Features#define: Object-like Macros#elif: Elif#else: Else#endif: Ifdef#error: Diagnostics#ident: Other Directives#if: Conditional Syntax#ifdef: Ifdef#ifndef: Ifdef#import: Alternatives to Wrapper #ifndef#include: Include Syntax#include_next: Wrapper Headers#line: Line Control#pragma GCC dependency: Pragmas#pragma GCC poison: Pragmas#pragma GCC system_header: Pragmas#pragma GCC system_header: System Headers#sccs: Other Directives#unassert: Obsolete Features#undef: Undefining and Redefining Macros#warning: Diagnostics