#define and #undef

用法：

#define DEBUG

#undef DEBUG

#if , #elif , #else , and #endif

用法：

#if DEBUG

#endif

#warning and #error

用法：

#if DEBUG && RELEASE

#error "You've defined DEBUG AND RELEASE simultaneously!"

#endif

#warning "Don't forget to remove this line before the boss tests the code!"

#region and #endregion

用法：

#region Member Field Declarations

xx

#endregion

#line

用法：

#line 164 "Core.cs"

#line default

#pragma

用法：

#pragma warning disable 169

xxx

#pragma warning restore 169

#nullable

用法：

#nullable enable

#nullable disable

#nullable restore