Eclipse C/C++ Shows Errors but Compiles?

Question

So I am building some Arduino code in eclipse, as described in Your Second Arduino Project, but every time I use an Arduino library, such as Serial, Eclipse und

Answer 1

In my case the problem was due to adding "-std=c++17" flag in the language standard field in the project properties under the compile dialect. After that the build was passing with errors, but the program was running fine. So the trick of Index>Rebuild resolved everything.