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How to set preprocessor macro based on Project Settings variable?

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    How to set preprocessor macro based on Project Settings variable?

    Hi there! I'm wondering how I would go about defining a macro based on the value of a variable in my project settings?

    Specifically, I'm working on a plugin for an inventory system and I'd like to define some macros that will compile/exclude certain parts of the code based on the type of inventory system I want (of which there are two "types" right now). I have a custom project settings category implemented with a single boolean variable. I'd like that boolean variable to be used to define a macro, such as INVENTORY_TYPE_SLOT, so that I can compile/exclude what I need.

    For example it'd look something like this:
    Code:
    // In MyProjectSettings.h
    bool bToggleInventorySystemType;
    
    // In WhereverTheHellI'dDefineMyMacros.something
    #define INVENTORY_TYPE_SLOT bToggleInventorySystemType
    #define INVENTORY_TYPE_LIST !bToggleInventorySystemType
    There very well could be alternate solutions to what I'm trying to do (I don't want to do if/else conditions with the variable though since that still compiles all the code), but if you have any ideas how I could do what I described above I'd love to hear it.

    Additionally, would there be any important differences from the solution to the former problem and defining a macro from an enum or int? I suspect not, but honestly I don't really know as I've never tried something like this.

    #2
    You should look into how to use the C++ Preprocessor :-)

    What you want to do to completely compile something out conditionally, is

    Code:
    #define USE_FEATURE_ONE
    ...
    #ifdef USE_FEATURE_ONE
    code that implements "feature one"
    #endif
    ...
    #ifdef USE_FEATURE_TWO
    code that implements "feature two"
    #endif
    now, what you can't do, is connect a run-time variable (bool bToggleInventorySystemType) to a pre-processor macro -- the game doesn't exist at build time. If you want to compile it all out, you have to do it with a #define

    Comment


      #3
      Setting preprocessor defines conditionally like that needs to be done in the module's build.cs file. For example, from the Steam controller plugin:

      PHP Code:
      bool bSteamSDKFound Directory.Exists(Target.UEThirdPartySourceDirectory "Steamworks/" SteamVersion) == true;
      PublicDefinitions.Add("STEAMSDK_FOUND=" + (bSteamSDKFound "1" "0")); 
      You can read config files using ConfigCache.ReadHierarchy(), you can see an example in Engine\Plugins\Lumin\MagicLeap\Source\MLSDK\MLSDK.Build.cs

      Comment


        #4
        good point! still not a setting in game, but I completely failed to consider the build.cs system. I'm still pretty new to this.

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