forward declaration issue with ustructs

Development Programming & Scripting C++
1

hi,

forward declaration works fine with UCLASS-es, but I get the following compilation error when try to do it with USTRUCT-s (e.g.: “struct FRTSPlayer;”) to use them in other USTRUCT-s:

…Unrecognized type ‘FRTSPlayer’ - type must be a UCLASS, USTRUCT or UENUM

and several other error messages are coming, pointing to lines where that struct type is used, and compilation fails.

Another strange thing comes when I modify USTRUCT() to USTRUCT(BlueprintType), then the message above appears but the compilation is completed successfully, but only when the struct is defined in the header file containing a UCLASS. if it is in a separate file it fails.

I normally add new .h/.cpp files to the project by right clicking source folder or a subfolder in solution explorer, and select add item. I also add always the #include “…generated.h” line and macros properly. Basically, everything else works fine.

Maybe I do something wrong, or it would be better to use UObject in similar cases, when they should be referenced in other UStructs?

thanks.

2

What do you mean by ‘use them in other USTRUCTs’?
If you mean embedding them like:



USTRUCT()
struct X
{
  UPROPERTY()
  struct A a;
};

then that isn’t possible in C++ at all. Member variables which aren’t pointers/references need to have their type fully defined.
If that’s what you’re doing, then yeah you’ll get a UHT error, but actually it’s irrelevant, since it couldn’t compile even if the UHT pass succeeded.

3

sorry if I was unclear, something like the following, e.g. to store a pointer in child structs to the owner struct, set by parent struct or GameMode:


USTRUCT(BlueprintType)
struct FRTSPlayer
{
    GENERATED_USTRUCT_BODY()

...

    // own units
    UPROPERTY()
    FRTSUnitManager RTSUnitManager;

...

};




USTRUCT()
struct FRTSUnitManager
{
    GENERATED_USTRUCT_BODY()

...

    UPROPERTY()
    FRTSPlayer* RTSPlayer;

...

};
4

Okay. Pointers to structs aren’t supported as UPROPERTYs. Structs are essentially used as value types within the UE4 property system.
If you remove the UPROPERTY() line, it should work fine with a forward declaration.

5

thank for the prompt answer, it works now!
I have not found info about this limitation in the docs…
now I simply have to decide whether switch to UObject or not…