Multiple inheritance not working with UClass

Development Programming & Scripting C++
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1

Hello,

I’m trying to extend a class from ACharacter and another own character class to add some attributes and methods to it.

UCLASS()
class TRIBES_API ANPC : public ACharacter , public gurps::Character
{
	GENERATED_UCLASS_BODY()

	UPROPERTY(EditAnywhere, Category = Behavior)
	class UBehaviorTree *NPCBehavior;

};

The compilation fails with "error: IN NPC: Missing ‘{’ in ‘Class’. Does someone have an idea what is going on ?
When i comment the “, public gurps::Character” out it compiles just fine. Also if i extend a non UClass with my own character class it works fine, so the class itself shouldn’t contain any errors.

Thank you!

2

UCLASS classes can not have multiple inherited classes, except for interfaces. So each UCLASS can only have one direct inherited class and as many interfaces (UINTERFACE) classes as you want.

3

Thank you! The 2nd class i want to inherit from is from an external library, i guess it is not possible then to extend it since i cannot add additional code to it ?

4

I believe you can extend it with just a normal class (not a UCLASS). You could do something like the following (I have not tested this):

class MyExtendedClass : public gurps::Character
{
   public:
       void SomeFunction( );
};

UCLASS()
class TRIBES_API ANPC : public ACharacter
{
   GENERATED_UCLASS_BODY()

   MyExtendedClass* SomeData;
};

and do all your work through the SomeData pointer, rather than through inheritance.

5

Thank you again! I just make it an attribute then like you suggested.

6

Btw, this pattern is called “Composition”. It helps to reduce dependency betweed different classes. And it is a good practice to use composition instead of inheritance in most cases. Base classes that will support inheritance should be writed very carefully and follow SOLID as much as possible.

7

Maybe something has changed since 2014. You can derive your UCLASS from multiple classes if only one is itself a UCLASS. The others can be interfaces or regular classes that are not derived from UE4 classes. For example:

class MyStandardCPPClass : public WhateverIfNecessary
{
 //...
}

UCLASS()
class MY_API AMyActor : public AActor, public MyStandardCPPClass
{
  GENERATED_BODY()
  // ...
}

That kind of thing works in my project (4.14.1).