I use eclipse cdt and I included some files. Unfortunalty I cannot add the include path to my eclipse project since then eclipse will always crash when it starts indexing the newly added includes. Therefore I would like to turn off the feature that highlights errors.
Where can I do this?
This is probably not the answer to your problem, but it's actually the answer to your question (which I was looking for and now found out myself): How to disable the red underlining, which can be pretty annoying because it hides underscore characters.
Go to Preferences -> General -> Editors -> Text Editors -> Annotations
(Alternative: Type "annotations" in the filter / search box).
In the "Annotation types" list, select "Errors". Disable the "Text as" setting (to the right).
The same can be done for yellow underlining of warnings (further down in the list).
You might try to disable the indexer, if that is really the problem. If you are using indigo release (or one of its milestones or release candidates), try to disable Codan's checkers. Workspace-or-project properties/preferences C++ Code Analysis. This should get rid of the underlining. Codan is relatively new, and at least pre-release had some issues with some of the code checkers.