LNK 2001 error caused by virtual interface

Development Programming & Scripting UI
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1

I’ve been trying to implement a simple interface into my project Damageable. It contains a single virtual method Damage(float damage). Everything appears to be fine with intellisense, however when the project is compiled in the editor it throws the following error

Error D:\GamesCreate\Reflections\Reflections\Binaries\Win64\UE4Editor-Reflections-1327.dll : fatal error LNK1120: 1 unresolved externals
Error ReflectionsCharacter.cpp.obj : error LNK2001: unresolved external symbol “public: virtual void __cdecl AReflectionsCharacter::Damage(float)” (?Damage@AReflectionsCharacter@@UEAAXM@Z)
Error Reflections.generated.cpp.obj : error LNK2001: unresolved external symbol “public: virtual void __cdecl AReflectionsCharacter::Damage(float)” (?Damage@AReflectionsCharacter@@UEAAXM@Z)

my code for my interface is as follows

// Fill out your copyright notice in the Description page of Project Settings.

#pragma once

#include "CoreMinimal.h"
#include "DamageableInterface.generated.h"

// This class does not need to be modified.
UINTERFACE(MinimalAPI)
class UDamageableInterface : public UInterface
{
	GENERATED_BODY()
};

/**
 * 
 */
class REFLECTIONS_API IDamageableInterface
{
	GENERATED_BODY()

	// Add interface functions to this class. This is the class that will be inherited to implement this interface.
public:
	virtual void Damage(float damage) = 0;
	
};

It seems like such a simple task to create a pure virtual function within an interface, but I cannot figure out how to implement it. I think it has something to do with the function being virtual, however I don’t know where to go from here. Why is this error being thrown and what can I do to fix it?

2

Based on the log output, it looks like it’s your AReflectionsCharacter class that’s throwing the error.

The “unresolved external symbol” error often appears when you declare a function in your class header file, but don’t define it in any source (.cpp) files.

In your case, my guess is, you’ve set your AReflectionsCharacter class to inherit from your new interface, but haven’t yet defined and declared an override for the interface’s Damage(…) function.

Have a look at that and let me know if that’s what’s going on.