Upgrade version from 4.26 to UE5

Development Getting Started & Setup
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Hello,

I am sorry if my question is not on the correct catergory, i wasn’t able to find any category that suits better.

So, I have a big project in 4.26 and I am trying to upgrade to UE5… My project is mainly in BP, but I have some C++ in it (not much at all, just a merge mesh).

So, I installed UE5, installed my plugins, installed visual studio 2022… etc… I had a lot of issue with “Fail to load editor” or things like that, but at the end I manage to resolve it and have a last issue but I don’t find the solution :

To be able to launch the project, I had to open the visual studio solution and rebuild it. But I don’t manage to make the build works… There is problem with my C++ code (merge mesh) that was initially working fine in 4.26. Problems are the following :

  1. Some of my includes don’t work (impossible to open…)
    #include “SkeletalMeshMerge.h”
    #include “Engine/SkeletalMeshSocket.h”
    #include “Engine/SkeletalMesh.h”
    #include “Animation/Skeleton.h”
    I don’t know why, it was working fine before, and it is UE4 and 5 files so I don’t know why… Maybe the path isn’t correct ? But why it has change ? One important fact is my UE5 is on my other HDD, and my UE4 was on my SDD. But I am not sure that it is linked… It is supposed to be able to find the files, no ?
    I then have a lot of other errors but I think major parts are linked to the include failed.
    EDIT : I tried to change the path by “D://Program Files/Epic Games/UE_5.0/Engine/Source…” etc for each include and yes then it is able to open it… But now there is much more include that it can’t open (in skeleton.h for example…)

  2. I have a message “GDuplicate struct name: SkelMeshMergeUVTransformMapping also exists in file D:\Program Files\EpicGames\UE_5.0\Engine\Source\Runtime\Engine\Public\SkeletalMeshMerge.h”

Does it mean that in UE5 they created a structure that have exactly the same name as mine ? It is strange. Am I understanding right ? I will try to change my structure name to be sure.
Fact is that I do my mesh merge code using the help in the documentation of UE4 on merge mesh (that at this time wasn’t really good with a lot of errors in code…). Maybe they directly create it in UE5 that is why some of my structure already exist ?

With this two main problem I am not able to build my project anymore.
Would you like to help me please?

Thank you a lot everybody for your time.

All the best