--- title: "Unreal C++" author: "Perrin Yong" author_profile: https://www.pystone.net/profile/ published_by: "Perrin Yong" canonical: https://www.pystone.net/notes/unreal-cpp/ type: note content_role: unspecified visibility: public id_stability: rename-stable source_path: "10-计算机、信息技术与工程/05-游戏图形与运行时/Unreal/Unreal C++.md" content_hash: 3638f45527b128c73dbb14c298bf3d592907fcedceeb3a46d7cfb4af785c61dd knowledge_version: 224c990773de.5fa8af6e39fa site_commit: 224c990773de166d23a886306577dd90379529ce notes_commit: 5fa8af6e39fa3891d1b9b4832bfa6c4e0ecaaf0a --- # Unreal C++ # Unreal C++ > 创建时间：2022/3/11 19:11 * 概念 * Compiling * * 我的Q&A * Class Naming Prefix * 关于宏定义 * C++宏定义 * 可变宏 * 运算符：#，## * 宏定义 vs. typedef * 宏定义 vs. 函数 * 其他技巧与细节 * Unreal宏定义 * UCALSS * MYPROJECT_API * Unreal宏编译 * 宏定义的方式 * 常用宏配置与Unreal Editor中的效果 * Objects & GC * Update * Destroy * Memory Management & GC * Root Set * Non-UObject References * 智能指针 * 常用类型 * Numeric Types * Strings * FString * FText * FName * TCHAR * Containers * TArray - std::vector * TMap - std::map * TSet - std::set * Cumtom TSet/TMap * Ref ## 概念 Forward Declaration ![assets/Unreal-C++__Image.png](/media/653ee82d9a20040f65c2.png) ## Compiling ### https://docs.unrealengine.com/4.27/en-US/ProductionPipelines/DevelopmentSetup/CompilingProjects/ ## 我的Q&A ### Class Naming Prefix Actor - A Object - U Enums - E Interface - I Template - T SWidget - S F - else ## 关于宏定义 ### C++宏定义 编译过程 ![assets/Unreal-C++__Image_1.png](/media/e7042ab54bca7a9d32f9.png) ![assets/Unreal-C++__Image_2.png](/media/12999ec4dd2b7ba73eb2.png) https://blog.csdn.net/yanggangclcsdn/article/details/49704089 每个#define行（即逻辑行）由三部分组成： ```xml public class AGenericClass<T> where T : IComparable<T> { } ``` 指令 - “#”表示这是一条预处理命令，“define”为宏命令 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 替换文本”-任意常数、表达式、字符串等 包括 有参宏 和 无参宏 两种 #### 可变宏 ```xml public class AGenericClass<T> where T : IComparable<T> { } ``` #### 运算符：#，## ```xml public class AGenericClass<T> where T : IComparable<T> { } ``` ```xml public class AGenericClass<T> where T : IComparable<T> { } ``` "##" 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）** ”。 #### 宏定义 vs. typedef ```xml public class AGenericClass<T> where T : IComparable<T> { } ``` 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。 #### 宏定义 vs. 函数 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。 ```xml public class AGenericClass<T> where T : IComparable<T> { } ``` COUNT(++x) 被替换为 ++x * ++x，即为 7 * 8 = 56，而不是想要 7 * 7 = 49 不要在有参宏用使用到“++”、“–”等 #### 其他技巧与细节 换行：在结尾加反斜杠，可使多行连接 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。 如果重复定义宏，则不同的编译器采用不同的重定义策略。 ### Unreal宏定义 #### UCALSS The UCLASS macro gives the UObject a reference to a UCLASS that describes its Unreal-based type. UE4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。 每个 UCLASS 保留一个称作“类默认对象（Class Default Object）”的对象，简称 CDO。 The 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. Another advantage of using UCLASS() is that you can use **Unreal Engine's memory management system** in the C++ class. > UCLASS宏只能修饰UObject的子类。 类型说明符（Class Specifiers） ![assets/Unreal-C++__Image_3.png](/media/b8c53f0d7fb15529aa52.png) 元数据说明符（Metadata Specifiers） ![assets/Unreal-C++__Image_4.png](/media/91801a0e2f3a0275b785.png) #### MYPROJECT_API Specifying MYPROJECT_API is necessary if MyProject wishes to expose the UMyObject class to other modules. #### Unreal宏编译 The compilation of an Unreal C++ project happens in two phases. 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. 2. In the second phase, the C++ compiler compiles the resulting code. ```xml public class AGenericClass<T> where T : IComparable<T> { } ``` For 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. #### 宏定义的方式 C++代码中定义 Build.cs文件和Target.cs文件中 ```xml public class AGenericClass<T> where T : IComparable<T> { } ``` 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。 #### 常用宏配置与Unreal Editor中的效果 https://blog.csdn.net/qq_29523119/article/details/85255854 ## Objects & GC https://docs.unrealengine.com/4.27/en-US/ProgrammingAndScripting/ProgrammingWithCPP/UnrealArchitecture/Objects/ 内存分配与容器：https://www.cnblogs.com/kekec/p/12012537.html ### Update ### Destroy ## Memory Management & GC **UE4 uses the reflection system to implement a garbage collection system.** Your classes need to derive from **UObject** in order to be enabled for garbage collection. An 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. If 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. The engine runs the garbage collector at certain **intervals**. > UStructs cannot be garbage collected. ### Root Set UObject pointer stored in a UPROPERTY in a UE4 container Actors: GC druing a level's shutdown Once spawned, you must manually call Destroy on them to remove them from the Level without ending the Level. This 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. RootSet操作与判断 ```xml public class AGenericClass<T> where T : IComparable<T> { } ``` ### Non-UObject References Normal 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 ### 智能指针 ## 常用类型 ### Numeric Types int8/uint8: 8-bit signed/unsigned integer int16/uint16: 16-bit signed/unsigned integer int32/uint32: 32-bit signed/unsigned integer int64/uint64: 64-bit signed/unsigned integer float (32-bit) and double (64-bit) types ### Strings #### FString FString is a mutable string, analogous to std::string. ```xml public class AGenericClass<T> where T : IComparable<T> { } ``` #### FText localized text ??? ```xml public class AGenericClass<T> where T : IComparable<T> { } ``` ```xml public class AGenericClass<T> where T : IComparable<T> { } ``` #### FName Rather 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. * save memory when that string is used across many objects * save CPU time when comparing them- UE4 can simply check their index values to see if they match #### TCHAR The TCHAR type is used as a way of storing characters independent of the character set being used https://docs.unrealengine.com/4.27/en-US/ProgrammingAndScripting/ProgrammingWithCPP/UnrealArchitecture/StringHandling/CharacterEncoding/ ### Containers 相关资料：v ```xml public class AGenericClass<T> where T : IComparable<T> { } ``` #### TArray - std::vector like std::vector, offers a lot more functionality ```xml public class AGenericClass<T> where T : IComparable<T> { } ``` #### TMap - std::map has quick methods for finding, adding, and removing elements based on their key #### TSet - std::set AddUnique, Contains - **faster** #### Cumtom TSet/TMap you will need to provide a **hash function** that takes a const pointer or reference to your type and returns a uint32 This return value is known as the object's **hash code** , and should uniquely identify the object. ## Ref https://blog.csdn.net/yanggangclcsdn/article/details/49704089 https://romeroblueprints.blogspot.com/2020/10/the-uclass-macro.html https://www.geek-share.com/detail/2802042559.html https://docs.unrealengine.com/4.27/en-US/ProgrammingAndScripting/ProgrammingWithCPP/IntroductionToCPP/