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03-UnrealEngine/Gameplay/UObject/UnrealSpecifiers/Specifier/USTRUCT/UHT/NoExport/NoExport.md

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+# NoExport
+
+- **功能描述：** 指定UHT不要用来自动生成注册的代码，而只是进行词法分析提取元数据。
+- **元数据类型：** bool
+- **引擎模块：** UHT
+- **常用程度：★**
+
+指定UHT不要用来自动生成注册的代码，而只是进行词法分析提取元数据。
+
+NoExportTypes.h里使用了很多该例子。定义的结构常常用!CPP宏包起来以不在C++中参与编译。因此一般是只给引擎内部使用的。
+
+实际上我们想使用也可以，只要保持C++中内存布局一样，就可以自己多定义。使用场景：想自己定义一个UHT头喂给UHT分析，然后自己在别处定义实际的C++。一种典型用途是C++里的实际多个类继承于一个模板基类，如FVector2MaterialInput，这样可以每个特化子类定一个UHT类型别名。另一种目的是把UHT要分析的头文件都放在一个文件里，加速UHT分析生成，不用分析多个文件，反正只要UHT信息和内存布局对就行。
+
+```cpp
+#if !CPP	// begin noexport class
+USTRUCT(noexport, BlueprintType) //如果不写noexport，会报错：Expected a GENERATED_BODY() at the start of the struct、
+struct FFloatRK4SpringInterpolator
+{
+	
+	UPROPERTY(EditAnywhere, Category = "FloatRK4SpringInterpolator")
+	float StiffnessConstant;
+
+	/** 0 = Undamped, <1 = Underdamped, 1 = Critically damped, >1 = Over damped */
+	UPROPERTY(EditAnywhere, Category = "FloatRK4SpringInterpolator")
+	float DampeningRatio;
+
+	bool bIsInitialized;
+	bool bIsInMotion;
+	float TimeRemaining;
+	FRK4SpringConstants SpringConstants;
+
+	float LastPosition;
+	RK4Integrator::FRK4State<float> State;
+};
+#endif	// end noexport class
+
+//实际应用：
+template <typename T>
+struct FRK4SpringInterpolator
+{
+protected:
+	float StiffnessConstant;
+	float DampeningRatio;
+
+	bool bIsInitialized;
+	bool bIsInMotion;
+	float TimeRemaining;
+	FRK4SpringConstants SpringConstants;
+
+	T LastPosition;
+	RK4Integrator::FRK4State<T> State;
+}
+
+struct FFloatRK4SpringInterpolator : FRK4SpringInterpolator<float>
+struct FVectorRK4SpringInterpolator : FRK4SpringInterpolator<FVector>
+```
+
+不生成的代码包括：
+
+```cpp
+USTRUCT(BlueprintType,noexport)
+struct INSIDER_API FMyStruct_NoExport
+{
+	//抑制：GENERATED_BODY()解释生成的：
+	//static class UScriptStruct* StaticStruct();	
+
+	UPROPERTY(BlueprintReadWrite, EditAnywhere)
+	float Score;
+};
+
+//抑制：
+//template<> INSIDER_API UScriptStruct* StaticStruct<struct FMyStruct_NoExport>();
+```
+
+ .h里不会生成，因此不会在别的模块里使用
+
+```cpp
+template<> INSIDER_API UScriptStruct* StaticStruct<struct FMyStruct_NoExport>();
+```
+
+但是依然会在Module.init.gen.cpp里生成Z_Construct_UScriptStruct_FMyStruct_NoExport的调用，因此还是会在蓝图里暴露出来。
+
+```cpp
+#include "UObject/GeneratedCppIncludes.h"
+PRAGMA_DISABLE_DEPRECATION_WARNINGS
+void EmptyLinkFunctionForGeneratedCodeInsider_init() {}
+	INSIDER_API UScriptStruct* Z_Construct_UScriptStruct_FMyStruct_NoExport();
+	static FPackageRegistrationInfo Z_Registration_Info_UPackage__Script_Insider;
+	FORCENOINLINE UPackage* Z_Construct_UPackage__Script_Insider()
+	{
+		if (!Z_Registration_Info_UPackage__Script_Insider.OuterSingleton)
+		{
+			static UObject* (*const SingletonFuncArray[])() = {
+					(UObject* (*)())Z_Construct_UScriptStruct_FMyStruct_NoExport,//这里注入调用
+			};
+			static const UECodeGen_Private::FPackageParams PackageParams = {
+				"/Script/Insider",
+				SingletonFuncArray,
+				UE_ARRAY_COUNT(SingletonFuncArray),
+				PKG_CompiledIn | 0x00000000,
+				0x02A7B98C,
+				0xFA17C3C4,
+				METADATA_PARAMS(0, nullptr)
+			};
+			UECodeGen_Private::ConstructUPackage(Z_Registration_Info_UPackage__Script_Insider.OuterSingleton, PackageParams);
+		}
+		return Z_Registration_Info_UPackage__Script_Insider.OuterSingleton;
+	}
+	static FRegisterCompiledInInfo Z_CompiledInDeferPackage_UPackage__Script_Insider(Z_Construct_UPackage__Script_Insider, TEXT("/Script/Insider"), Z_Registration_Info_UPackage__Script_Insider, CONSTRUCT_RELOAD_VERSION_INFO(FPackageReloadVersionInfo, 0x02A7B98C, 0xFA17C3C4));
+PRAGMA_ENABLE_DEPRECATION_WARNINGS
+```
+
+蓝图里的效果：依然可以当作变量。
+
+![Untitled](Untitled.png)
+
+![Untitled](Untitled%201.png)
+
+加上noexport的区别是不能用StaticStruct和没了TCppStructOps，不能做一些优化。其他还是可以正常使用，就像FVector一样。
+
+缺失的代码，也可以通过手动添加代码来获得。
+
+```cpp
+USTRUCT(BlueprintType,noexport)
+struct INSIDER_API FMyStruct_NoExport
+{
+	//GENERATED_BODY()	//missing type specifier - int assumed，..generated.h里只是定一个StaticStruct()函数
+
+	static class UScriptStruct* StaticStruct();	//可以自己定义
+
+	UPROPERTY(BlueprintReadWrite, EditAnywhere)
+	float Score;
+
+};
+
+template<> INSIDER_API UScriptStruct* StaticStruct<struct FMyStruct_NoExport>();//可以自己定义
+
+//.cpp
+//链入函数声明，在其他的cpp里已经有实现，所以可以正常调用到
+INSIDER_API UScriptStruct* Z_Construct_UScriptStruct_FMyStruct_NoExport();
+UPackage* Z_Construct_UPackage__Script_Insider();
+
+static FStructRegistrationInfo Z_Registration_Info_UScriptStruct_MyStruct_NoExport;
+
+class UScriptStruct* FMyStruct_NoExport::StaticStruct()
+{
+	if (!Z_Registration_Info_UScriptStruct_MyStruct_NoExport.OuterSingleton)
+	{
+		Z_Registration_Info_UScriptStruct_MyStruct_NoExport.OuterSingleton = GetStaticStruct(Z_Construct_UScriptStruct_FMyStruct_NoExport, Z_Construct_UPackage__Script_Insider(), TEXT("MyStruct_NoExport"));
+	}
+	return Z_Registration_Info_UScriptStruct_MyStruct_NoExport.OuterSingleton;
+}
+
+template<> INSIDER_API UScriptStruct* StaticStruct<FMyStruct_NoExport>()
+{
+	return FMyStruct_NoExport::StaticStruct();
+}
+```