I have mixed C++ / Java project in Eclipse. I\'ve setup a build.mk file and Eclipse builds project successfully when all files in editor are closed. When I open a .h or a .c
I finally figured this out. Flushing the Eclipse Indexer as mentioned in the top voted answer didn't work for me. This is what I had to do:
I went to: Project -> Properties -> C/C++ General -> Paths and Symbols -> Includes
Here I had the path for my include directory, but what I had to do was delete the directory path, and then re-add it making sure to check the box "Add to all configurations". I also checked the box "Add to all languages", but I don't think that is necessary.
After this, you may need to then click on Project -> C/C++ Index -> Rebuild. I didn't need to, but you might. Also, obviously instead of C/C++ in the paths above, it will be Java or whatever language you are dealing with.