[visual-studio] ERROR: Cannot open source file " "

I am running visual studio C++ and I have a header file "GameEngine.h" that I am trying to have another file see.

When I #include "GameEngine.h" it gives me the error that it cannot open the source file. I have no idea what to do. I have done this literally a thousand times but for some reason this is now not working.

One thing that caught me out and surprised me was, in an inherited project, the files it was referring to were referred to on a relative path outside of the project folder but yet existed in the project folder.

In solution explorer, single click each file with the error, bring up the Properties window (right-click, Properties), and ensure the "Relative Path" is just the file name (e.g. MyMissingFile.cpp) if it is in the project folder. In my case it was set to: ..\..\Some Other Folder\MyMissingFile.cpp.

Just in case there is someone out there who's a bit new like me, double check that you are spelling your header folders correctly.

For example:

<#include "Component/BoxComponent.h"

This will result in the error. Instead, it needs to be:

<#include "Components/BoxComponent.h"

1. Copy the contents of the file,
2. Create an .h file, give it the name of the original .h file
3. Copy the contents of the original file to the newly created one
4. Build it
5. VOILA!!

Let Unreal do the job. Close all, Right click your Project File (.uproject),
"Generate VisualStudio Project Files".

This was the top result when googling "cannot open source file" so I figured I would share what my issue was since I had already included the correct path.

I'm not sure about other IDEs or compilers, but least for Visual Studio, make sure there isn't a space in your list of include directories. I had put a space between the ; of the last entry and the beginning of my new entry which then caused Visual Studio to disregard my inclusion.