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  "contentMarkdown": "# Unreal C++\n\n# Unreal C++\n\n> 创建时间：2022/3/11 19:11\n\n* 概念\n  * Compiling\n    *   * 我的Q&A\n    * Class Naming Prefix\n  * 关于宏定义\n    * C++宏定义\n      * 可变宏\n      * 运算符：#，##\n      * 宏定义 vs. typedef\n      * 宏定义 vs. 函数\n      * 其他技巧与细节\n    * Unreal宏定义\n      * UCALSS\n      * MYPROJECT_API\n      * Unreal宏编译\n      * 宏定义的方式\n      * 常用宏配置与Unreal Editor中的效果\n  * Objects & GC\n    * Update\n    * Destroy\n  * Memory Management & GC\n    * Root Set\n    * Non-UObject References\n    * 智能指针\n  * 常用类型\n    * Numeric Types\n    * Strings\n      * FString\n      * FText\n      * FName\n      * TCHAR\n    * Containers\n      * TArray - std::vector\n      * TMap - std::map\n      * TSet - std::set\n      * Cumtom TSet/TMap\n  * Ref\n\n## 概念\n\nForward Declaration\n\n![](assets/Unreal-C++__Image.png)\n\n## Compiling\n\n###\n\nhttps://docs.unrealengine.com/4.27/en-US/ProductionPipelines/DevelopmentSetup/CompilingProjects/\n\n## 我的Q&A\n\n### Class Naming Prefix\n\nActor - A\n\nObject - U\nEnums - E\nInterface - I\nTemplate - T\nSWidget - S\nF - else\n\n## 关于宏定义\n\n### C++宏定义\n\n编译过程\n\n![](assets/Unreal-C++__Image_1.png)\n\n![](assets/Unreal-C++__Image_2.png)\n\nhttps://blog.csdn.net/yanggangclcsdn/article/details/49704089\n\n每个#define行（即逻辑行）由三部分组成：\n\n```xml\npublic class AGenericClass<T> where T : IComparable<T> { }\n\n```\n\n指令 - “#”表示这是一条预处理命令，“define”为宏命令\n宏（macro） - 一般为缩略语，其名称（宏名）一般大写，而且不能有空格，遵循C变量命令规则\n替换文本”-任意常数、表达式、字符串等\n\n包括 有参宏 和 无参宏 两种\n\n#### 可变宏\n\n```xml\npublic class AGenericClass<T> where T : IComparable<T> { }\n\n```\n\n#### 运算符：#，##\n\n```xml\npublic class AGenericClass<T> where T : IComparable<T> { }\n\n```\n```xml\npublic class AGenericClass<T> where T : IComparable<T> { }\n\n```\n\n\"##\" 运算符也可以用在替换文本中，而它的作用是起到粘合的作用，即将两个语言符号组合成一个语言符号，所以又称为“ **预处理器的粘合剂（Preprocessor Glue）** ”。\n\n#### 宏定义 vs. typedef\n\n```xml\npublic class AGenericClass<T> where T : IComparable<T> { }\n\n```\n\n宏定义只是简单的字符串代换，在预处理阶段完成。而typede不是简单的字符串代换，而是可以用来做类型说明符的重命名的，类型的别名可以具有类型定义说明的功能，在编译阶段完成的。\n\n#### 宏定义 vs. 函数\n\n所以在宏定义中：#define COUNT(M) M * M 中的形参不分配内存单元，所以不作类型定义。而函数 int count(int x)中形参是局部变量，会在栈区分配内存单元，所以要作类型定义，而且实参与形参之间是“值传递”。而宏只是符号代换，不存在值传递。\n\n```xml\npublic class AGenericClass<T> where T : IComparable<T> { }\n\n```\n\nCOUNT(++x) 被替换为 ++x * ++x，即为 7 * 8 = 56，而不是想要 7 * 7 = 49\n不要在有参宏用使用到“++”、“–”等\n\n#### 其他技巧与细节\n\n换行：在结尾加反斜杠，可使多行连接\n\n宏定义必须写在函数之外，其作用域是 #define 开始，到源程序结束。\n\n如果重复定义宏，则不同的编译器采用不同的重定义策略。\n\n### Unreal宏定义\n\n#### UCALSS\n\nThe UCLASS macro gives the UObject a reference to a UCLASS that describes its Unreal-based type.\nUE4有一个管理游戏对象的强大系统。UObject是这个系统中所有对象的基类。UCLASS宏用于标记这些UObject的派生类，目的是把它们告知UObject管理系统。UCLASS的宏参数可以更加具体地指定该类型的各种行为。\n\n每个 UCLASS 保留一个称作“类默认对象（Class Default Object）”的对象，简称 CDO。\n\nThe UCLASS() macro is used to indicate that a C++ class will be part of Unreal's **Reflection system**. This is necessary for the C++ class to be recognized by the Unreal Engine editor.\nAnother advantage of using UCLASS() is that you can use **Unreal Engine's memory management system** in the C++ class.\n\n> UCLASS宏只能修饰UObject的子类。\n\n类型说明符（Class Specifiers）\n\n![](assets/Unreal-C++__Image_3.png)\n\n元数据说明符（Metadata Specifiers）\n\n![](assets/Unreal-C++__Image_4.png)\n\n#### MYPROJECT_API\n\nSpecifying MYPROJECT_API is necessary if MyProject wishes to expose the UMyObject class to other modules.\n\n#### Unreal宏编译\n\nThe compilation of an Unreal C++ project happens in two phases.\n\n  1. In the first phase, UnrealHeaderTool (UHT) reads the C++ headers files looking for Unreal macros and generates the necessary code that will replace the macros.\n  2. In the second phase, the C++ compiler compiles the resulting code.\n\n```xml\npublic class AGenericClass<T> where T : IComparable<T> { }\n\n```\n\nFor this class, UnrealHeaderTool will generate code that will be placed in the TutoProjectCollectable.generated.h file and code that will replace the GENERATED_BODY() macro.\n\n#### 宏定义的方式\n\nC++代码中定义\n\nBuild.cs文件和Target.cs文件中\n\n```xml\npublic class AGenericClass<T> where T : IComparable<T> { }\n\n```\n\n在UBT代码的文件夹（`\\Engine\\Source\\Programs\\UnrealBuildTool`）中搜索Definitions.Add就可以看到编译时添加的宏定义。\n\n#### 常用宏配置与Unreal Editor中的效果\n\nhttps://blog.csdn.net/qq_29523119/article/details/85255854\n\n## Objects & GC\n\nhttps://docs.unrealengine.com/4.27/en-US/ProgrammingAndScripting/ProgrammingWithCPP/UnrealArchitecture/Objects/\n\n内存分配与容器：https://www.cnblogs.com/kekec/p/12012537.html\n\n### Update\n\n### Destroy\n\n## Memory Management & GC\n\n**UE4 uses the reflection system to implement a garbage collection system.**\n\nYour classes need to derive from **UObject** in order to be enabled for garbage collection.\n\nAn object will **not be garbage collected** as long as **there is a path of references from an object in the root set to the object** in question.\n\nIf no such path to the root set exists for an object, it is called **unreachable** and will be **collected (deleted)** the next time the garbage collector runs.\n\nThe engine runs the garbage collector at certain **intervals**.\n\n> UStructs cannot be garbage collected.\n\n### Root Set\n\nUObject pointer stored\nin a UPROPERTY\nin a UE4 container\n\nActors:\nGC druing a level's shutdown\nOnce spawned, you must manually call Destroy on them to remove them from the Level without ending the Level.\n\nThis is important since, as mentioned before, **actors that have had Destroy called on them are not removed until the garbage collector runs again**. You can check the **IsPendingKill** method to see if a UObject is awaiting its deletion.\n\nRootSet操作与判断\n\n```xml\npublic class AGenericClass<T> where T : IComparable<T> { }\n\n```\n\n### Non-UObject References\n\nNormal C++ objects (not derived from UObject) can also have the ability to add a reference to an object and prevent garbage collection --- derive from **FGCObject** and override its **AddReferencedObjects** method\n\n### 智能指针\n\n## 常用类型\n\n### Numeric Types\n\nint8/uint8: 8-bit signed/unsigned integer\n\nint16/uint16: 16-bit signed/unsigned integer\n\nint32/uint32: 32-bit signed/unsigned integer\n\nint64/uint64: 64-bit signed/unsigned integer\n\nfloat (32-bit) and double (64-bit) types\n\n### Strings\n\n#### FString\n\nFString is a mutable string, analogous to std::string.\n\n```xml\npublic class AGenericClass<T> where T : IComparable<T> { }\n\n```\n\n#### FText\n\nlocalized text ???\n\n```xml\npublic class AGenericClass<T> where T : IComparable<T> { }\n\n```\n```xml\npublic class AGenericClass<T> where T : IComparable<T> { }\n\n```\n\n#### FName\n\nRather than storing the complete string many times across every object that references it, FName uses a smaller storage footprint index that maps to a given string.\n\n  * save memory when that string is used across many objects\n  * save CPU time when comparing them- UE4 can simply check their index values to see if they match\n\n#### TCHAR\n\nThe TCHAR type is used as a way of storing characters independent of the character set being used\n\nhttps://docs.unrealengine.com/4.27/en-US/ProgrammingAndScripting/ProgrammingWithCPP/UnrealArchitecture/StringHandling/CharacterEncoding/\n\n### Containers\n\n相关资料：v\n\n```xml\npublic class AGenericClass<T> where T : IComparable<T> { }\n\n```\n\n#### TArray - std::vector\n\nlike std::vector, offers a lot more functionality\n\n```xml\npublic class AGenericClass<T> where T : IComparable<T> { }\n\n```\n\n#### TMap - std::map\n\nhas quick methods for finding, adding, and removing elements based on their key\n\n#### TSet - std::set\n\nAddUnique, Contains - **faster**\n\n#### Cumtom TSet/TMap\n\nyou will need to provide a **hash function** that takes a const pointer or reference to your type and returns a uint32\nThis return value is known as the object's **hash code** , and should uniquely identify the object.\n\n## Ref\n\nhttps://blog.csdn.net/yanggangclcsdn/article/details/49704089\nhttps://romeroblueprints.blogspot.com/2020/10/the-uclass-macro.html\nhttps://www.geek-share.com/detail/2802042559.html\nhttps://docs.unrealengine.com/4.27/en-US/ProgrammingAndScripting/ProgrammingWithCPP/IntroductionToCPP/\n"
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