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Plugin : How to properly include a struct


in my Plugin I've got a Object which inherits from UObject. It's name is Watcher. Inside Watcher.h I declared a USTRUCT FMyStruct. The struct consists of some FVectors. Then I've got another Object inherited from UObject called Tracer. Watcher has a member of type Tracer. I want Tracer to do LineTraces , so i declared a method with Parameter MyStruct. Inside Watcher.h I included Tracer.h . Inside Tracer.h I included Watcher.h . Compiler can't resolve type of parameter FMyStruct in void Trace(..) . I've tried different includes. None worked for me. How do I include properly?

 #include "Tracer.h"
 #include "Watcher.generated.h"
 struct FMyStruct
 class UWatcher : public UObject
     FMyStruct values;
     UTracer* tracer;


  #include "Watcher.h"
 #include "Tracer.generated.h"
     class UTracer : public UObject
         FHitResult Hitresult;
         void Trace(FMyStruct values);

Product Version: UE 4.17
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asked Nov 15 '17 at 10:02 PM in C++ Programming

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avatar image ColdSteel48 Nov 15 '17 at 10:46 PM

I have the same problem - unfortunately you will have to move your struct to the tracer.h otherwise it will not work :(

avatar image ColdSteel48 Nov 15 '17 at 10:49 PM

Normally in C++ you would use forward declaration, but it doesn't work in this scenario when you are messing with USTRUCTS - onse possible solution is to promote it to UCLASS and then forward declare. Another solution I suppose would be to use TWeakPTR.

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1 answer: sort voted first

You can use forward type declarations here. For example in your header you can write

 // #include "Fish.h"
 void SomeFunctionEatingFish(class UFish* fresh);

without including files with UFish declarations. This method have limitations - you can declare only pointers or references of unknown classes and can't use any methods of this class in the file before including a header related to the class. When creating a .cpp file you still have to include all required headers to use your classes.

If it's not applicable you can move your UStruct declaration to a separate file and include it both from watcher and tracer files.

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answered Nov 15 '17 at 10:54 PM

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avatar image kosmopilot Nov 15 '17 at 10:57 PM

Thanks, type declartion works :)

avatar image c4tnt Nov 15 '17 at 11:00 PM

Ooops, it's actually forward type declarations, I skipped that word...

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