unreal-cpp-gameplay

Unreal C++ Gameplay

Write correct UE5 gameplay C++: the reflection macros that connect C++ to the editor and Blueprints, the Gameplay Framework class roles, and module dependencies. Targets UE 5.8.

When to use

• Use when creating C++ gameplay classes (AActor, APawn, ACharacter, AGameModeBase, UActorComponent), exposing properties/functions with UPROPERTY/UFUNCTION, setting up a GameMode's default classes, or adding a module dependency in *.Build.cs.
• Use when the project has a Source/ tree with *.h/*.cpp using UCLASS, and *.Build.cs.

When not to use: designer-facing visual logic → unreal-blueprints. Player input binding details → unreal-enhanced-input. AI logic → unreal-behavior-trees. This skill owns the C++ class/reflection foundation those build on.

Core workflow

1. Name with the right prefix. A = Actor-derived, U = UObject/component-derived, F = plain struct, E = enum, I = interface. The prefix must match the base class.
2. Declare the class with reflection macros. UCLASS() above the class, GENERATED_BODY() as the first line in the body, and #include "ClassName.generated.h" as the last include in the header.
3. Expose data with UPROPERTY (editor/Blueprint visibility and garbage-collection tracking) and behaviour with UFUNCTION (BlueprintCallable, etc.).
4. Create components in the constructor with CreateDefaultSubobject<T>(TEXT("Name")) and set the RootComponent.
5. Know the framework roles: AGameModeBase sets the rules + default classes; APawn/ ACharacter is the controllable body; APlayerController is the player's will; UActorComponent is reusable behaviour.
6. Add module dependencies to *.Build.cs (e.g. EnhancedInput) or unresolved-symbol link errors follow.
7. Verify by compiling (Live Coding Ctrl+Alt+F11 for function bodies; full rebuild for header/UPROPERTY changes) and checking the class/properties appear in the editor.

Patterns

1. Minimal Actor class (header + source)

// Pickup.h
#pragma once
#include "CoreMinimal.h"
#include "GameFramework/Actor.h"
#include "Pickup.generated.h"          // MUST be the last include

UCLASS()
class MYGAME_API APickup : public AActor   // MYGAME_API = your module's export macro
{
    GENERATED_BODY()
public:
    APickup();

    // EditAnywhere = tweak per-instance & on the CDO; BlueprintReadWrite = BP get/set.
    UPROPERTY(EditAnywhere, BlueprintReadWrite, Category = "Pickup")
    int32 ScoreValue = 10;

    // UPROPERTY on a UObject* pointer is what keeps it from being garbage-collected.
    UPROPERTY(VisibleAnywhere)
    TObjectPtr<UStaticMeshComponent> Mesh;   // UE5: TObjectPtr instead of raw UStaticMeshComponent*

    UFUNCTION(BlueprintCallable, Category = "Pickup")
    void Collect();

protected:
    virtual void BeginPlay() override;
};

// Pickup.cpp
#include "Pickup.h"
#include "Components/StaticMeshComponent.h"

APickup::APickup()
{
    Mesh = CreateDefaultSubobject<UStaticMeshComponent>(TEXT("Mesh"));
    RootComponent = Mesh;                     // the mesh is this actor's root
}

void APickup::BeginPlay() { Super::BeginPlay(); }   // always call Super
void APickup::Collect()   { Destroy(); }

2. GameMode wiring its default classes

// MyGameMode.cpp — set in the constructor so the engine spawns your classes.
AMyGameMode::AMyGameMode()
{
    DefaultPawnClass      = AMyCharacter::StaticClass();
    PlayerControllerClass = AMyPlayerController::StaticClass();
}

3. Module dependency in Build.cs

// MyGame.Build.cs
PublicDependencyModuleNames.AddRange(new string[]
{
    "Core", "CoreUObject", "Engine", "InputCore", "EnhancedInput"
});

Pitfalls

• generated.h not last / missing — compile errors like "Cannot find generated header" or "Expected an include". It must be the final include in the header.
• Forgetting GENERATED_BODY() — UHT (Unreal Header Tool) errors; it must be the first thing inside the class body.
• Raw UObject* without UPROPERTY — the garbage collector doesn't see it and may destroy it out from under you. Track every UObject pointer with UPROPERTY (use TObjectPtr in UE5).
• Header/UPROPERTY edits with Live Coding — Live Coding handles function bodies, but changes to UCLASS/UPROPERTY/headers need a full editor restart + rebuild.
• Wrong class prefix — naming an Actor UFoo (or a component AFoo) breaks UHT; match the prefix to the base type.
• Unresolved external symbol at link — the module providing the API isn't in Build.cs PublicDependencyModuleNames.
• Not calling Super:: in overridden BeginPlay/Tick/etc. skips engine setup.

References

• For UActorComponent creation/attachment, the UPROPERTY garbage-collection ownership rules (TObjectPtr, TArray<TObjectPtr<>>, AddToRoot), and a replication primer, read references/components-and-gc.md.
• Primary docs: "Unreal Engine CPP Quick Start" and "Gameplay Framework" (https://dev.epicgames.com/documentation/en-us/unreal-engine/gameplay-framework-in-unreal-engine).

Related skills

• unreal-blueprints — exposing C++ to designers; BP/C++ interop.
• unreal-enhanced-input — binding input in a C++ Pawn/Character.
• unreal-behavior-trees — C++ AI tasks driven from a behaviour tree.