unreal-engine-cpp-pro

# Unreal Engine C++ Pro This skill provides expert-level guidelines for developing with Unreal Engine 5 using C++. It focuses on writing robust, performant, and standard-compliant code. ## When to Use Use this skill when: - Developing C++ code for Unreal Engine 5.x projects - Writing Actors, Components, or UObject-derived classes - Optimizing performance-critical code in Unreal Engine - Debugging memory leaks or garbage collection issues - Implementing Blueprint-exposed functionality - Following Epic Games' coding standards and conventions - Working with Unreal's reflection system (UCLASS, USTRUCT, UFUNCTION) - Managing asset loading and soft references Do not use this skill when: - Working with Blueprint-only projects (no C++ code) - Developing for Unreal Engine versions prior to 5.x - Working on non-Unreal game engines - The task is unrelated to Unreal Engine development ## Core Principles 1. **UObject & Garbage Collection**: * Always use `UPROPERTY()` for `UObject*` member variables to ensure they are tracked by the Garbage Collector (GC). * Use `TStrongObjectPtr<>` if you need to keep a root reference outside of a UObject graph, but prefer `addToRoot()` generally. * Understand the `IsValid()` check vs `nullptr`. `IsValid()` handles pending kill state safely. 2. **Unreal Reflection System**: * Use `UCLASS()`, `USTRUCT()`, `UENUM()`, `UFUNCTION()` to expose types to the reflection system and Blueprints. * Minimize `BlueprintReadWrite` when possible; prefer `BlueprintReadOnly` for state that shouldn't be trampled by logic in UI/Level BPs. 3. **Performance First**: * **Tick**: Disable Ticking (`bCanEverTick = false`) by default. Only enable it if absolutely necessary. Prefer timers (`GetWorldTimerManager()`) or event-driven logic. * **Casting**: Avoid `Cast<T>()` in hot loops. Cache references in `BeginPlay`. * **Structs vs Classes**: Use `F` structs for data-heavy, non-UObject types to reduce overhead. ## Naming Conventions (Strict) Follow Epic Games' coding standard: * **Templates**: Prefix with `T` (e.g., `TArray`, `TMap`). * **UObject**: Prefix with `U` (e.g., `UCharacterMovementComponent`). * **AActor**: Prefix with `A` (e.g., `AMyGameMode`). * **SWidget**: Prefix with `S` (Slate widgets). * **Structs**: Prefix with `F` (e.g., `FVector`). * **Enums**: Prefix with `E` (e.g., `EWeaponState`). * **Interfaces**: Prefix with `I` (e.g., `IInteractable`). * **Booleans**: Prefix with `b` (e.g., `bIsDead`). ## Common Patterns ### 1. Robust Component Lookup Avoid `GetComponentByClass` in `Tick`. Do it in `PostInitializeComponents` or `BeginPlay`. ```cpp void AMyCharacter::PostInitializeComponents() { Super::PostInitializeComponents(); HealthComp = FindComponentByClass<UHealthComponent>(); check(HealthComp); // Fail hard in dev if missing } ``` ### 2. Interface Implementation Use interfaces to decouple systems (e.g., Interaction system). ```cpp // Interface call check if (TargetActor->Implements<UInteractable>()) { IInteractable::Execute_OnInteract(TargetActor, this); } ``` ### 3. Async Loading (Soft References) Avoid hard references (`UPROPERTY(EditDefaultsOnly) TSubclassOf<AActor>`) for massive assets which force load orders. Use `TSoftClassPtr` or `TSoftObjectPtr`. ```cpp UPROPERTY(EditAnywhere, BlueprintReadWrite) TSoftClassPtr<AWeapon> WeaponClassToLoad; void AMyCharacter::Equip() { if (WeaponClassToLoad.IsPending()) { WeaponClassToLoad.LoadSynchronous(); // Or use StreamableManager for async } } ``` ## Debugging * **Logging**: Use `UE_LOG` with custom categories. ```cpp DEFINE_LOG_CATEGORY_STATIC(LogMyGame, Log, All); UE_LOG(LogMyGame, Warning, TEXT("Health is low: %f"), CurrentHealth); ``` * **Screen Messages**: ```cpp if (GEngine) GEngine->AddOnScreenDebugMessage(-1, 5.f, FColor::Red, TEXT("Died!")); ``` * **Visual Logger**: extremely useful for AI debugging. Implement `IVisualLoggerDebugSnapshotInterface`. ## Checklist before PR - [ ] Does this Actor need to Tick? Can it be a Timer? - [ ] Are all `UObject*` members wrapped in `UPROPERTY`? - [ ] Are hard references (TSubclassOf) causing load chains? Can they be Soft Ptrs? - [ ] Did you clean up verified delegates in `EndPlay`? ## Limitations - Use this skill only when the task clearly matches the scope described above. - Do not treat the output as a substitute for environment-specific validation, testing, or expert review. - Stop and ask for clarification if required inputs, permissions, safety boundaries, or success criteria are missing.