# Structs, how to initialize one as a variable?

**URL:** <https://forums.unrealengine.com/t/structs-how-to-initialize-one-as-a-variable/47745>\
**Category:** C++\
**Tags:** unreal-engine\
**Created:** [November 17, 2015, 11:53pm UTC](https://forums.unrealengine.com/t/structs-how-to-initialize-one-as-a-variable/47745 "2015-11-17T23:53:59Z")\
**Posts on this page:** 6\
**Page:** 1

<div class="post-metadata">

**Author:** ![JmDevTx](https://d3kjluh73b9h9o.cloudfront.net/original/4X/2/8/5/28502927f1d97ba1051b3b47ccfe17233bf41ef0.png) [@JmDevTx](https://forums.unrealengine.com/u/JmDevTx)\
**Post date:** [November 17, 2015, 11:53pm UTC](https://forums.unrealengine.com/t/structs-how-to-initialize-one-as-a-variable/47745/1 "2015-11-17T23:53:59Z")

</div>

I have a struct that I am using, and all is well, except for the fact that I can’t seem to initialize my struct. I am trying to do:

```auto

FMyStruct TestStruct(Params)

```

, but am getting an error saying that there is no default constructor. I am also getting no hint as to which parameters my struct needs. I want to see a hint like this:  
 ![a4eec26e7a.png](https://d3kjluh73b9h9o.cloudfront.net/original/4X/b/e/5/be51b90cd626feef73b9707d50264d678dfcd1b3.png)

Here is how I declare my struct:

```auto

USTRUCT(Blueprintable)
struct FMyStruct
{
	GENERATED_USTRUCT_BODY()
		UPROPERTY(EditAnywhere, BlueprintReadWrite, Category = "My Struct")
			 FName MotherNanny;
		UPROPERTY(EditAnywhere, BlueprintReadWrite, Category = "My Struct")
			FName KeyRing;
		UPROPERTY(EditAnywhere, BlueprintReadWrite, Category = "My Struct")
			float Scones;
};

```

The exact thing I am trying to do is:

```auto

MyArrayOfStructs.Add(FMyStruct("Nanny's Mother", "Keyed Car", 2))

```

What am I missing?

---

<div class="post-metadata">

**Author:** ![xulture](https://d1ap1mz92jnks1.cloudfront.net/user_avatar/forums.unrealengine.com/xulture/32/921486_2.png) [@xulture](https://forums.unrealengine.com/u/xulture)\
**Post date:** [November 18, 2015, 12:15am UTC](https://forums.unrealengine.com/t/structs-how-to-initialize-one-as-a-variable/47745/2 "2015-11-18T00:15:21Z")

</div>

```auto

USTRUCT(Blueprintable)
struct FMyStruct
{
	GENERATED_BODY()

	// default constructor -- without parameters, so it will work inside other structures 
	// that need default initializer, such as TArray
	FMyStruct()
	: MotherNanny(TEXT("")), KeyRing(TEXT("")), Scones(-1.f)
	{}

	// constructor that takes 3 parameters
	FMyStryct(const FName& InMotherNanny, const FName& InKeyRing, float InScones)
	: MotherNanny(InMotherNanny), KeyRing(InKeyRing), Scones(InScones)
	{}

	UPROPERTY(EditAnywhere, BlueprintReadWrite, Category = "My Struct")
	FName MotherNanny;

	UPROPERTY(EditAnywhere, BlueprintReadWrite, Category = "My Struct")
	FName KeyRing;

	UPROPERTY(EditAnywhere, BlueprintReadWrite, Category = "My Struct")
	float Scones;
};

```

---

<div class="post-metadata">

**Author:** ![JmDevTx](https://d3kjluh73b9h9o.cloudfront.net/original/4X/2/8/5/28502927f1d97ba1051b3b47ccfe17233bf41ef0.png) [@JmDevTx](https://forums.unrealengine.com/u/JmDevTx)\
**Post date:** [November 18, 2015, 1:04am UTC](https://forums.unrealengine.com/t/structs-how-to-initialize-one-as-a-variable/47745/3 "2015-11-18T01:04:33Z")

</div>

> [@xulture;421812](#):
>
> ```auto
> 
> USTRUCT(Blueprintable)
> struct FMyStruct
> {
> GENERATED_BODY()
> 
> // default constructor -- without parameters, so it will work inside other structures 
> // that need default initializer, such as TArray
> FMyStruct()
> : MotherNanny(TEXT("")), KeyRing(TEXT("")), Scones(-1.f)
> {}
> 
> // constructor that takes 3 parameters
> FMyStryct(const FName& InMotherNanny, const FName& InKeyRing, float InScones)
> : MotherNanny(InMotherNanny), KeyRing(InKeyRing), Scones(InScones)
> {}
> 
> UPROPERTY(EditAnywhere, BlueprintReadWrite, Category = "My Struct")
> FName MotherNanny;
> 
> UPROPERTY(EditAnywhere, BlueprintReadWrite, Category = "My Struct")
> FName KeyRing;
> 
> UPROPERTY(EditAnywhere, BlueprintReadWrite, Category = "My Struct")
> float Scones;
> };
> 
> ```

Thanks! So from what I understand, a struct constructor is like the name implies, a constructor that runs when the struct constructed, and sets the struct’s variables based on what was passed to the constructor.

---

<div class="post-metadata">

**Author:** ![xulture](https://d1ap1mz92jnks1.cloudfront.net/user_avatar/forums.unrealengine.com/xulture/32/921486_2.png) [@xulture](https://forums.unrealengine.com/u/xulture)\
**Post date:** [November 18, 2015, 1:58am UTC](https://forums.unrealengine.com/t/structs-how-to-initialize-one-as-a-variable/47745/4 "2015-11-18T01:58:12Z")

</div>

Yepp that’s true…

I think that macro GENERATED\_BODY() for structs provides default constructor (while GENERATED\_USTRUCT\_BODY() does not). So that would have been enough to overcome compilation error.

However, you also need constructor with 3 parameters for your initialization while adding to TArray.

---

<div class="post-metadata">

**Author:** ![xulture](https://d1ap1mz92jnks1.cloudfront.net/user_avatar/forums.unrealengine.com/xulture/32/921486_2.png) [@xulture](https://forums.unrealengine.com/u/xulture)\
**Post date:** [November 18, 2015, 2:20am UTC](https://forums.unrealengine.com/t/structs-how-to-initialize-one-as-a-variable/47745/5 "2015-11-18T02:20:41Z")

</div>

There are few more tricks you can do to your Struct to get them even more TArray-friendly.

Below is one of the structs we have in our game; note that we don’t explicitly add default constructor, “GENERATED\_BODY()” does that for us, based on assignment in declaration, eg DamageMax = 0;

At the end, we overload “less than”, and “is equal” operators, to allow TArray.Sort() and TArray.Find(). In our case, effect (buff or debuff) is considered identical if it came from the same ParentAbility (spell) is the same effect index (when spells have more than one effect), came from the same instigator, and has the same name. We consider effect “smaller” than other effect, if time remaining is smaller.

```auto

USTRUCT(BlueprintType)
struct FAbilityEffect
{
	GENERATED_BODY()

	// Effect Type
	UPROPERTY(EditAnywhere, BlueprintReadWrite, Category = AbilityEffect)
		EAbilityEffectType Type;

	// Minimum damage, if applicable
	UPROPERTY(EditAnywhere, BlueprintReadWrite, Category = AbilityEffect)
		int32 DamageMin = 0;

	// Maximum damage, if applicable
	UPROPERTY(EditAnywhere, BlueprintReadWrite, Category = AbilityEffect)
		int32 DamageMax = 0;

	// Area affected in cm, if applicable
	UPROPERTY(EditAnywhere, BlueprintReadWrite, Category = AbilityEffect)
		float AreaRadius = 0.f;

	// Flag whether damage gets added to current weapon's damage
	UPROPERTY(EditAnywhere, BlueprintReadWrite, Category = AbilityEffect)
		bool AddToWeapon = false;

	// Duration in seconds
	UPROPERTY(EditAnywhere, BlueprintReadWrite, Category = AbilityEffect)
		float Duration = 0.f;

	// Stat Modifier (for Buffs and Debuffs)
	UPROPERTY(EditAnywhere, BlueprintReadWrite, Category = AbilityEffect)
		EStatModifier StatModifier;

	// Modification amount absolute (negative for debuffs, positive for buffs)
	UPROPERTY(EditAnywhere, BlueprintReadWrite, Category = AbilityEffect)
		float ModifierAmount = 0.f;

	// Modification amount percentage/fraction (1.0 is no change, 0.7 for 30% debuff, 1.3 for 30% buff)
	UPROPERTY(EditAnywhere, BlueprintReadWrite, Category = AbilityEffect)
		float ModifierPercentage = 1.f;

	// Leap Inpulse
	UPROPERTY(EditAnywhere, BlueprintReadWrite, Category = AbilityEffect)
		float LeapImpulse = 0;

	// particle effect while under the influence
	UPROPERTY(EditAnywhere, BlueprintReadWrite, Category = VisualEffects)
		UParticleSystem* EffectParticle = NULL;

	UPROPERTY(EditAnywhere, BlueprintReadWrite, Category = VisualEffects)
		TSubclassOf<AActor> EffectReplacementActorClass = NULL;

	// grounnd hit decal, on the ground of the hit (eg at the feet or enemy)
	UPROPERTY(EditAnywhere, BlueprintReadWrite, Category = VisualEffects)
		TSubclassOf<class ADecalActor> GroundDecalClass;

	// flag to enable right leg trails
	UPROPERTY(EditAnywhere, BlueprintReadWrite, Category = Properties)
		bool RightLegTrails = false;

	// flag to enable left leg trails
	UPROPERTY(EditAnywhere, BlueprintReadWrite, Category = Properties)
		bool LeftLegTrails = false;

	// animation montage while effect active
	UPROPERTY(EditAnywhere, BlueprintReadWrite, Category = Properties)
		UAnimMontage* Animation = NULL;

	UPROPERTY(BlueprintReadOnly, Category = RuntimeParams)
		UParticleSystemComponent* EffectParticleComponent = NULL;
	UPROPERTY(BlueprintReadOnly, Category = RuntimeParams)
		AActor* EffectReplacementActor = NULL;
	UPROPERTY(BlueprintReadOnly, Category = RuntimeParams)
		FString Name;
	UPROPERTY(BlueprintReadOnly, Category = RuntimeParams)
		ATraverseBaseCharacter* Instigator = NULL;
	UPROPERTY(BlueprintReadOnly, Category = RuntimeParams)
		int32 Index = 0;
	UPROPERTY(BlueprintReadOnly, Category = RuntimeParams)
		float fRemainingTime = 0.f;
	UPROPERTY(BlueprintReadOnly, Category = RuntimeParams)
		int32 iRemainingTime = 0;
	UPROPERTY(BlueprintReadOnly, Category = RuntimeParams)
		float RemainingModifierAmount = 0.f;

	UPROPERTY(BlueprintReadOnly, Category = RuntimeParams)
		UAbility* ParentAbility = nullptr;

	// support for TArray.Sort() -- we sort on float time remaining
	FORCEINLINE bool operator<(const FAbilityEffect& V) const
	{
		return fRemainingTime < V.fRemainingTime;
	}

	// support for TArray.Find()
	FORCEINLINE bool operator==(const FAbilityEffect& Other) const
	{
		if (Index != Other.Index) return false;
		if (ParentAbility != Other.ParentAbility) return false;
		if (Instigator != Other.Instigator) return false;
		if (Name != Other.Name) return false;
		return true;
	}

};

```

---

<div class="post-metadata">

**Author:** ![JmDevTx](https://d3kjluh73b9h9o.cloudfront.net/original/4X/2/8/5/28502927f1d97ba1051b3b47ccfe17233bf41ef0.png) [@JmDevTx](https://forums.unrealengine.com/u/JmDevTx)\
**Post date:** [November 18, 2015, 4:52am UTC](https://forums.unrealengine.com/t/structs-how-to-initialize-one-as-a-variable/47745/6 "2015-11-18T04:52:35Z")

</div>

> [@xulture;421859](#):
>
> There are few more tricks you can do to your Struct to get them even more TArray-friendly.
> 
> Below is one of the structs we have in our game; note that we don’t explicitly add default constructor, “GENERATED\_BODY()” does that for us, based on assignment in declaration, eg DamageMax = 0;
> 
> At the end, we overload “less than”, and “is equal” operators, to allow TArray.Sort() and TArray.Find(). In our case, effect (buff or debuff) is considered identical if it came from the same ParentAbility (spell) is the same effect index (when spells have more than one effect), came from the same instigator, and has the same name. We consider effect “smaller” than other effect, if time remaining is smaller.
> 
> ```auto
> 
> USTRUCT(BlueprintType)
> struct FAbilityEffect
> {
> GENERATED_BODY()
> 
> // Effect Type
> UPROPERTY(EditAnywhere, BlueprintReadWrite, Category = AbilityEffect)
> EAbilityEffectType Type;
> 
> // Minimum damage, if applicable
> UPROPERTY(EditAnywhere, BlueprintReadWrite, Category = AbilityEffect)
> int32 DamageMin = 0;
> 
> // Maximum damage, if applicable
> UPROPERTY(EditAnywhere, BlueprintReadWrite, Category = AbilityEffect)
> int32 DamageMax = 0;
> 
> // Area affected in cm, if applicable
> UPROPERTY(EditAnywhere, BlueprintReadWrite, Category = AbilityEffect)
> float AreaRadius = 0.f;
> 
> // Flag whether damage gets added to current weapon's damage
> UPROPERTY(EditAnywhere, BlueprintReadWrite, Category = AbilityEffect)
> bool AddToWeapon = false;
> 
> // Duration in seconds
> UPROPERTY(EditAnywhere, BlueprintReadWrite, Category = AbilityEffect)
> float Duration = 0.f;
> 
> // Stat Modifier (for Buffs and Debuffs)
> UPROPERTY(EditAnywhere, BlueprintReadWrite, Category = AbilityEffect)
> EStatModifier StatModifier;
> 
> // Modification amount absolute (negative for debuffs, positive for buffs)
> UPROPERTY(EditAnywhere, BlueprintReadWrite, Category = AbilityEffect)
> float ModifierAmount = 0.f;
> 
> // Modification amount percentage/fraction (1.0 is no change, 0.7 for 30% debuff, 1.3 for 30% buff)
> UPROPERTY(EditAnywhere, BlueprintReadWrite, Category = AbilityEffect)
> float ModifierPercentage = 1.f;
> 
> // Leap Inpulse
> UPROPERTY(EditAnywhere, BlueprintReadWrite, Category = AbilityEffect)
> float LeapImpulse = 0;
> 
> // particle effect while under the influence
> UPROPERTY(EditAnywhere, BlueprintReadWrite, Category = VisualEffects)
> UParticleSystem* EffectParticle = NULL;
> 
> UPROPERTY(EditAnywhere, BlueprintReadWrite, Category = VisualEffects)
> TSubclassOf<AActor> EffectReplacementActorClass = NULL;
> 
> // grounnd hit decal, on the ground of the hit (eg at the feet or enemy)
> UPROPERTY(EditAnywhere, BlueprintReadWrite, Category = VisualEffects)
> TSubclassOf<class ADecalActor> GroundDecalClass;
> 
> // flag to enable right leg trails
> UPROPERTY(EditAnywhere, BlueprintReadWrite, Category = Properties)
> bool RightLegTrails = false;
> 
> // flag to enable left leg trails
> UPROPERTY(EditAnywhere, BlueprintReadWrite, Category = Properties)
> bool LeftLegTrails = false;
> 
> // animation montage while effect active
> UPROPERTY(EditAnywhere, BlueprintReadWrite, Category = Properties)
> UAnimMontage* Animation = NULL;
> 
> UPROPERTY(BlueprintReadOnly, Category = RuntimeParams)
> UParticleSystemComponent* EffectParticleComponent = NULL;
> UPROPERTY(BlueprintReadOnly, Category = RuntimeParams)
> AActor* EffectReplacementActor = NULL;
> UPROPERTY(BlueprintReadOnly, Category = RuntimeParams)
> FString Name;
> UPROPERTY(BlueprintReadOnly, Category = RuntimeParams)
> ATraverseBaseCharacter* Instigator = NULL;
> UPROPERTY(BlueprintReadOnly, Category = RuntimeParams)
> int32 Index = 0;
> UPROPERTY(BlueprintReadOnly, Category = RuntimeParams)
> float fRemainingTime = 0.f;
> UPROPERTY(BlueprintReadOnly, Category = RuntimeParams)
> int32 iRemainingTime = 0;
> UPROPERTY(BlueprintReadOnly, Category = RuntimeParams)
> float RemainingModifierAmount = 0.f;
> 
> UPROPERTY(BlueprintReadOnly, Category = RuntimeParams)
> UAbility* ParentAbility = nullptr;
> 
> // support for TArray.Sort() -- we sort on float time remaining
> FORCEINLINE bool operator<(const FAbilityEffect& V) const
> {
> return fRemainingTime < V.fRemainingTime;
> }
> 
> // support for TArray.Find()
> FORCEINLINE bool operator==(const FAbilityEffect& Other) const
> {
> if (Index != Other.Index) return false;
> if (ParentAbility != Other.ParentAbility) return false;
> if (Instigator != Other.Instigator) return false;
> if (Name != Other.Name) return false;
> return true;
> }
> 
> };
> 
> ```

That’s pretty cool! I am using my setup in a plugin, and receive errors when just using GENERATED\_BODY(), or it might be because I’m working in 4.6 lol.