C/C++ client/server indexer with integration for Emacs

 RTags is a client/server application that indexes C/C++ code and
 keeps a persistent file-based database of references, declarations,
 definitions, symbolnames etc. There’s also limited support for
 ObjC/ObjC++. It allows you to find symbols by name (including nested
 class and namespace scope). Most importantly it gives you proper
 follow-symbol and find-references support. It also have neat little
 things like rename-symbol, integration with clang’s “fixits”
 (https://clang.llvm.org/diagnostics.html).