Using #ifdef doesn't work with Unreal Header Tool

Development Programming & Scripting C++
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1

I’ve got some struct definitions for both C and C++ in one header, and using #if defined __cplusplus doesn’t seem to work with the unreal header tool.

My code looks like this:

   // Atmos.h
    #if defined __cplusplus || UE_GAME || UE_EDITOR || UE_SERVER
    #pragma once
    #include "Atmos.generated.h"
    
    USTRUCT(Blueprintable)
    struct FGases
    {
    	GENERATED_BODY()
    	...
    };
    
    USTRUCT()
    struct FAtmosVoxel
    {
    	GENERATED_BODY()
    	...
    };
    
    #else
    
    typedef struct
    {
    	...
    } AtmosVoxel;
    
    #endif

and trying to include it produces an error that the C++ structs are not USTRUCT types. When I comment out the preprocessor directives it works fine.

Do #ifdefs not work for the unreal header tool or am I doing something wrong? I read in another question that they were fixed

2

According to this answerhub post, it should work. Never used it in Unreal though, so I can’t tell.

You might have another bug in your code though.
You are using USTRUCT(Blueprintable) what you want is USTRUCT(BlueprintType) though.

Blueprintable exposes a class to BP allows subclassing of it. Unreal does not support subclasses of UStructs in BP (or anywhere for that matter).

3

That didn’t fix it

4

You don’t need the defined keyword. If it is not defined it is falsy.

You are doing the equivalent of this in the macro world:

if (I  < 5 || 10 || 17)

This is an illegal statement. The code you want is:

#if __cplusplus || UE_GAME || UE_EDITOR || UE_SERVER
5

That didn’t fix it

6

Isn’t __cplusplus always defined, so that’s the equivalent of #if 1. What is this #if statement supposed to do?

7

I’m including this header in OpenCL C, I want to place both struct types in one file for convenience

8

I looked through the Header Tool source and it looks like it doesn’t parse any if/ifdefs for C++, so I just wrote a BlueprintType wrapper struct in another file for the C/C++ struct