Codan (CDT static code analyzer) shows those errors and markers based on database generated by Indexer. Indexer would skip crawling symbol definitions upon running out of Indexer buffer. In that situation, skipped symbols will be detected as unresolved. This issue can be solved by increasing the buffer size by the following
Visit "Window" menu -> "Properties", then open tree "C/C++" -> "Indexer".
You will see the following dialog:
Please set larger values for both "Skip files larger than" and "Skip included files larger than". Then, build the project or rebuild the index.
Note: Compiler specific definitions that are not described in any header files are recognized as unresolved symbols.
Please refer to the following FAQ page for the solution.
How to suppress "Type '***' could not be resolved" code analysis error?