ue-cpp-foundations

UE C++ Foundations

You are an expert in Unreal Engine's C++ extensions and property system.

Context

Read .agents/ue-project-context.md for engine version, coding conventions, and project-specific rules. Engine version matters: UE5 uses TObjectPtr<> where UE4 used raw UObject*, and GENERATED_BODY() replaces GENERATED_USTRUCT_BODY() in structs.

Before You Start

Ask which area the user needs help with if unclear:

• Macros & Reflection — UCLASS, UPROPERTY, UFUNCTION, USTRUCT, UENUM
• Containers — TArray, TMap, TSet, TOptional
• Delegates — static, dynamic, multicast, binding patterns
• Strings — FName, FString, FText conversion and formatting
• Memory & GC — TObjectPtr, TWeakObjectPtr, TSharedPtr, GC roots
• Logging — UE_LOG, log categories, verbosity
• Subsystems — GameInstance, World, LocalPlayer subsystems

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UObject Macros & Reflection

All UE reflection macros require GENERATED_BODY() inside the class/struct and the corresponding .generated.h include.

UCLASS()

Specifier	Effect
Blueprintable	Blueprint subclassing allowed
BlueprintType	Usable as Blueprint variable
Abstract	Cannot be instantiated
NotBlueprintable	Blocks Blueprint subclassing
Config=<Name>	Loads UPROPERTY(Config) from <Name>.ini
Transient	Not saved/serialized
Within=<OuterClass>	Outer must be of given type

UCLASS(Blueprintable, BlueprintType)
class MYGAME_API UMyDataObject : public UObject
{
    GENERATED_BODY()
public:
    UMyDataObject();
};

Full specifier list: references/property-specifiers.md.

UPROPERTY()

UCLASS(Blueprintable)
class MYGAME_API AMyCharacter : public ACharacter
{
    GENERATED_BODY()
public:
    UPROPERTY(EditAnywhere, BlueprintReadWrite, Category="Stats")
    float MaxHealth = 100.f;

    UPROPERTY(VisibleAnywhere, BlueprintReadOnly, Category="Stats")
    float CurrentHealth;

    UPROPERTY(EditDefaultsOnly, BlueprintReadOnly, Category="Config")
    int32 MaxLevel = 50;

    UPROPERTY(ReplicatedUsing=OnRep_Health, Category="Replication")
    float ReplicatedHealth;

    UPROPERTY(Transient)                             // Not serialized; GC still tracks
    TObjectPtr<UParticleSystemComponent> CachedFX;

    UPROPERTY(SaveGame, BlueprintReadWrite, Category="Persistence")
    int32 PlayerScore;

    UPROPERTY(EditAnywhere, BlueprintReadWrite, Category="Stats",
              meta=(ClampMin="0.0", ClampMax="1.0"))
    float DamageMultiplier = 1.f;

    UFUNCTION()
    void OnRep_Health();

    virtual void GetLifetimeReplicatedProps(
        TArray<FLifetimeProperty>& OutLifetimeProps) const override;
};